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NAVAL POSTGRADUATE SCHOOL-Monterey, California '
DTICE ELE C T
AD-A241 009- OCT 3 1991flII]Jtill 11111111111 10lL I lIllI0 U U
THESISANALYSIS OF AN EDDY-RESOLVING
GLOBAL OCEAN MODELIN THE TROPICAL INDIAN OCEAN
by
Erik Christopher Long
September 1990
Thesis Advisor: Albert J. Semtner, Jr.
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REPORT DOCUMENTATION PAGEla Report Security Classification Unclassified lb Restrictive Markings2a Security Classification Authority 3 Distribution Availability of Report2b Declassification/Downgrading -Schedule Approved for public release. distribution is unlimited.4 Performing Organization Report Number(s) 5 Monitoring-Organization Report Number(s)NPS-68-90-0086a Nan -of Performing Organization 6b Office Symbol 7i Name of Monitoring OrganizationNaval Postgraduate School If Applicable) OC Naval Postgraduate- School6c Address (city, state, and ZIP code) 7 b Address (city, state, and ZIP code)Monterey,,CA 93943-5000 Monterey. CA 93943-50008a -Name of Funding/Sponsonng Organzaton 8b Office Symbol -9- ProcuremeritetnstrumentIdentification NumbcrNational Science Foundation (If Aiwlicable) NSF Grant No. ATM-87059908c Address (city, state, and ZIP code) 10 Source of Funding Numbers
___________________________________________ I Program Feaint N'umb"~ I Pmriet ?N I Taik No WVork Unit Acccwin Is
11 Title (Include Security Classification) ANALYSIS OF AN EDDY-RESOLVING GLOBAL OCEAN MODEL INTHE TROPICAL INDIAN OCEAN12 Personal Author(s) Long, Erik Christopher13a Type of Report I 13b Time Covered -14 Date of Report (year month,day) 15 Page CountMaster's Thesis From To September 1990 15816 Suppicrentary Notation The views expressed in this thesis are those of the author and do not reflect-the officialpolicy or position of the Department of Defense or the U.S. Government.17 Cosati Codes 18 Subject Terms (continue on reverse if necessary and identify-by block number)Ficld Group Subgroup Oceanographic Numerical Modeling, Indian Ocean, Ocean General Circulation
II |Model. Eddy-Resolving. Somali Current. Tropical. Equatorial19 Abstract (continue on reverse ifnecessary and identify by block number)
This paper examines the Semtner and Chervin global ocean model in the tropical Indian Ocean. Theprimitive equation, eddy-resolving model co~ers a domain from 75'S to 65cN at a horizontal resolution of 1/2",with 20 vertical levels. In a nev, phase of an ongoing simulation, the wind stress has been changed from annualmean wind forcing to seasonal forcing, using the Hellerman and Rosenstein (1983) wind stress. The model is
shown to reproduce the seasonal features of the Indian Ocean circulation. The seasonally-reversing SomaliCurrent is simulated by the model, and includes seasonai undercurrents and a tvo-gyre system during thesouthvest monsoon. Westvard flow& occurs beneath the Southwest Monsoon Current during June and July. Themajor equatorial currents ef the two monsoon regimes are "ell-represented, including semiannual Wyrtki jets andthe Equatorial Undercurrent. The seasonal features of the marginally-resolved Leeuwin Current are present in themodel. Monthly mass transports ha - been calculated for the major equatorial currents, as well as the Pacific-Indonesian throughflov, and are consistent with obsenations. The structure of deep equatorial jets in the modelis highly baroclinic, an upA ard tilt in the jets from v est to east accounts for simultaneous N&estward and upward
phase propagation of the zonal velocity.20 Distribution/Availability of Abstract 21 Abstract Security Classification
[L] unclassified/unlimitcd E- same as report [] DTIC users Unclassified22a Name of Responsible Individual 22b Telephone (Include Area code) 22c Office SymbolAlbert J. Semtner, Jr (408) 646-3267 OC/SeDD FORM 1473, 84 MAR 83 APR edition may be used until exhausted security classification of this page
All other editions are obsolete Unclassified
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UnclassifiedSecurity Classification of this page
19 Abstract (continued)
The Haney (1971) method of prescribing surface heat flux, adapted to the Levitus (1982) data base, isanal) zed by comparing the model surface heat flux and monthly temperature fields with existing climatologies.The model is shown to exhibit an inherent interannual variability, despite the interannual invariance of the,% ind
stress. The small amount of interannual variability is superimposed on a strong seasonal cycle. Near-surface
currents in the model are in good agreement with existing studies of drifting surface buoys.
S/N 0102-LF-014-6601 security classification of this page
ii
Approved for public release; distribution is unlimited.
A005,* ForAnalysis of an Eddy-Resolving Global Ocean Model [j1TIS 11- ,i
in -the Tropical Indian Ocean- Dc rj.b'
b y J u n t i f L a t ! - a . . . . .
Erik Christopher Long Distri-ut an/ -
Lieutenant Commander, United States Navy A va.lability COA06B.A., Oberlin College, 1979
B.S.E.E., 'Washington University, 1979 niat pOial
Submitted in partial fulfillment of the requirements .....for the degree of
MASTER OF SCIENCE IN METEOROLOGY ANDPHYSICAL OCEANOGRAPHY
from the
NAVAL POSTGRADUATE SCHOOLSeptember, 1990
Author:Erik Chr to Long
Approved by: ,,. " FAlbert J. ntner, Jr., Thesis' isor
Mary L. Batteen, Second Reader
Curtis A. Collins, Chairman,Department of Oceanography
di
ABSTRACT
This paper examines the Semtner and Chervin global ocean model in the tropical
Indian Ocean. The primitive equation, eddy-resolving-model covers a domain from 75'S to
65°N at a horizontal resolution-of 1/20, with 20 vertical -levels. In a new phase of an
ongoing simulation, the wind stress has been changed from annual mean wind-forcing to
seasonal forcing, using the Hellerman and Rosenstein (1983) wind stress. The model is
shoN n to reproduce the seasonalafeatures of the Indian Ocean circulation. The seasonally-
reversing Somali Currentis simulated-by the-model, and-includes seasonal undercurrents
and a two-gyre system during the southwest monson. Westward-flow occ,, rs beneath the
Southwest Monsoon Current during June and July. The major equatorial currents of the
two monsoon regimes are well-represented, including semiannual Wyrtki jets and the
Equatorial Undercurrent. The seasonal features -of the marginally-resol% ed Leenwin
Current are pre-ent-in the-model. Monthly mass transports have-been calculated for the
major equatorial currents, as well as the Pacific-Indonesian throughflow, and dre consistent
with observations. The structure-of deep equatorial jets in- the model is highly baroclinic;
an upward tilt in the jets from west to east accounts for simultaneous westward and upward
phase propagation of the zonal velocity.
The Haney (1971) method of prescribing surface heat flux, adapted to tb,. Levitus
(1982) data base, is analyzed by comparing the model surface heat flux and monthly
temperature fields with existingclimatologies. The model is shown to t-xhibit an inherent
interannual variability, despite the interannual invariance-of the wind strcss. The small
amount of interannual variabilityis superimposee on a strong seasonal cycle. Near-surface
currents in the model-are in good agreement with existing studies of drifting surface buoys.
iv
TABLE OF CONTENTS-
I. INTRODUCTION .............................................................. 1.A. BACKGROUND ......................................................... 1B. THE INDIAN OCEAN...................................................... 3
Ii.THE MODEL .................................................................... 6
1ll. WIND- STRESS ............................................................... 10
IV. RESULTS....................................................................14
A. NEAR-SURFACE CURRENTS.......................................... 14
1. The Seasonal-Cycle.................................................... 14
2. The Wyrtki-Jet........................................................ 19B. THE EQUATORIAL UNDERCURRENT................................. 19C. DEEP CURRENTS........................................................21
D. THE LEEU WIN CURRENT............................................... 23E. SURFACE-HEAT FLUX .................................................. 25F. THE SOMALI CURRENT SYSTEM....................................... 28G. THROUGHFLOW IN THE INDONESIAN ARCHIPELAGO .............. 31
V. DISCUSSION AND CONCLUSIONS........................................... 33A. MODEL TEMPERATURE-VS. CLIMATOLOGY .......................... 33B. COMPARISON-WITH CURRENT DRIFTR STUDIES.................... 34
C. MASS TRANSPORTS .................................................... 35D. OBSERVATIONS FROM ANIMATION STUDIES ........................ 36E. CONCLUSIONS ......................................................... 38
APPENDIX (FIGURES) .......................................................... 40
LIST OF REFERENCES.......................................................... 137
INITIAL DISTRIBUTION LIST .................................................. 144
V
ACKNOWLEDGMENT
This work is supported by grants-ATM-8705980 and OCE-8812472 from the-National
Science Foundation. Computing resources were-provided by the Scientific Computing
Division of the National-Center for Atmospheric Research. NCAR is sponsored by the
-National Science Foundation.
The good Lord provided us with each other as our most valuable resource, and that
has not changed in this world- of microprocessors to- supercomputers. Mike McCann
p- )vided tremendous support involving the-model and the Ocean Processor, customization
of programs-to provide analysis products,and the animation of the -modelz output. This
project would not have been possible without his-assistance. Animation was developed
using software tools supplied by-the National Center for Supercomputer Applications.
Fritz Schott, Jim O'Biien, and Stuart Godfrey gave me the benefit- of their tremendous
experience in providing comments on the interpretation of the results. Bob Chervin
steadfastly ran-the=model on the Cray X-MP,-providing-a steady flow of output for me to
analyze. Curt Collins graciously allowed the use of his-Macintosh for preparing graphics,
and gave me the encouragement to show the model results at the TOGA conference. Tom
Bettge's Ocean Processor and supporting documentation enabled-:the straightforward
anlysis of the archived data, and his timely responses to questions simplified many
problems. My colleagues, Larry Gordon and Tom Murphree, provided mutual support and
valuable feedback in the model output analysis. Mary Batteen was a tremendous resource
in the comparison of the model output with observations and thesis prq-paration. My
fiancee, Whitney Fay, made me very-happy by distracting me from-working on my thesis,
until I needed to finish it, when she understandingly left'me alone. Mike VanWoert was
my role model in becoming an oceanographer without getting wet.
vi
Finally, Bert Semtner gave me the freedom to be Chief Oceanographer of the model
Indian Ocean, gave me-guidance when Ineeded it, -ptiently answered my questions.as I
gained understanding of ocean modeling, and made the project an enjoyable educational
experience.
Vii
I. INTRODUCTION
The Semtner and Chervin-(1988) study of global ocean circulation reported-the results
of an eddy-resolving global ocean model forced by mean annual climatological winds.
The purpose of this paper is to report on-the follow-on experiment, which forces the ocean
model with mean monthly wind stress. Due to the intense seasonal-cycle-of the tropical
monsoon, the change to seasonal forcing in the model was expected to have its greatest
impact in the tropics. This study examines the-seasonal cycle of the tropical Indian Ocean
in-the model.
A. BACKGROUND
The worldwide industrial growth of the 20th century has caused environmental
changes which man is only beginning to understand. The advent of global remote sensing
systems-has recently given us-the ability to-monitor-the effect that man has on the world
climate, yet we still know very little about the- time scales of naturally-occurring climatic
variabilit). We no% recognize-that there are important feedback mechanisms between the
atmosphere and the oceans, which must be understood if we are to be able to predict
climatic change. Computer simulation is the most promising tool for projecting the results
of increased atmospheric emissions by industrial activity, and it may help -predict the
environmental impact of pollution of the seas. The trends in increasing computer power
indicate that we may soon have sufficient computing resources available to conduct studies
of climatic change, using coupled air-ocean simulations with realistic physics. The recent
development of eddy-resolving global ocean models is a very important step in the
development of global climate modeling.
Simulations of the ocean circulation require approximately 1,000 times as much
computer power-as atmospheric-simulations,because-of the smaller space scales and-longer
-time scales of motion in the sea. Hence, researchers involved with general circulation
ocean modeling have always been limited in the scope of their studies-by the available
computer power. Although simulations of the global ocean circulation have been
performed-for more-than 20 years, the understanding of the important role of mesoscale
and sub-mesoscale features in the ocean requires that an ocean -model -must resolve
mesoscale eddies if it is to accurately portray the energetics and variability of the ocean.
While some global modeling strategies have attained mesoscale eddy-resolving resolution,
limitations-in computer power have required some limitation in the-modei physics, such-as
quasi-geostrophic or layered models. The Semtner and Chervin: model (Semtner and
Chervin (1988), Chervin and Semtner (1988)), hereafter referred to as SCM, is the first
attempt at-a primitive-equation, eddy-resolving global circulation simulation.
As physical limitations in semiconductor technology are reached, computational power
has cOntinued to increase through the use of supercomputer architecture employing
multiple, parallel processors. The SCM code was designed -to be able to exploit rapid
increases in computing power expected in the 1990's by being easily reconfigured-to run
on new models of Cray supercomputers, employing-up to 64 processors. Although the use
of multitasking may -afford significant speed increases, any bottlenecks in the program
(i. e., steps which must be-run on only one processor) severely restrict the speedup-gained
by addingadditional processors. This relationship isdescribed in Amdahl's Law:S -N (1)I+ s (N - 1)
where the speedup (S) to be gained by going from 1 processor to N processors is strongly
dependent upon N and s, the sequential fraction of program which must be performed on
one processor. As the number of processors becomes greater, the requirement for
2
-1
efficiency increases. The SCM-code results in:a sequential fraction of 0.0036, allowing it
to achieve a speedup factor of 3.96 when run on a four proct.:sor-machine, 7.80 on eight
processors, 15.18 on a 16-processor machine, and 52.17 on t 64-processor machine.
Ocean models will have to-become extraordinarily efficient to take n.-iximum advantage of
parallel processing. The SCM, when run-at 1/20 horizontal resolution (as ;n Semtner and
Chervin (1988) and this study), is only marginally eddy-resolving, but is fully capable of
greater resolution when run on more powerful machines.
B. THE INDIAN OCEAN
The surface currents in the Indian Ocean are divided into two seasonal regimes,
associated with the northeast and southwest monsoons. As shown in Figure 1.1(a), the
northeast monsoon regime consists of a system of zonal currents, defined from south-to
north by the Antarctic Circumpolar Current, the South Equatorial Current, the Equatorial
Countercurrent, and the North Equatorial Current. The southwest monsoon season
(Figure 1.1(b)) creates the powerful northeastward-flowing Somali Current, and a two-
gyre system defined by the the Antarctic Circumpolar Currrent, the South Equatorial
Current, and the Southwest Monsoon Current.
Oceanographic observations in the Indian Ocean have lagged those of the Atlantic and
Pacific Oceans, due -o the limited number of shipPing Ianes, long transit times and great
cost of sending oceanographic ships tQ the area from North American and European ports,
as well as limited financial and na,,al interests in the area by major oceanographic countries.
Figure 1.2(a) (from Levitus, 1982) shows the density of Indian Ocean surface and
subsurface temperature measurements, and-Figure 1.2(b) shows the distribution of surface
observations in the Indian Ocean from the Hanstenrath and Lamb (1979) atlas. The
coverage is very sparse outside of the shipping lanes.
This paucity of observations is quite significant, because the Indian Ocean has-many
unique and-seasonal features, which have-no analog in the Atlantic and Pacific Oceans.
The basin is closed to-the north, and the presence of the Asian continent causes several of
the unique Indian Ocean features. First, the monsoon cycle in the Indian Ocean is-much-
stronger than in the other oceans, due to such key elements as-heating of the Himalayan
massif, and intensification of winds along the African coast. Unlike the Atlantic and
Pacific Oceans, the Indian-Ocean has no communication with-northern polar or subpolar
waters. Furthermore, as described in Brekhovskikh et al., (1986), the presence of the
Indian subcontinent causes a significant east/west basin difference in moisture patterns.
The monsoon brings seasonal reversals of surface currents at several points in the Indian
Ocean, including the Somali Current, zonal surface currents at the Equator, the Leeuwin
Current, which flows into the prevailing wind, and the Equatorial Undercurrent.
Although equatorial undercurrents are known to exist in the Atlantic, Pacific, and
Indian Oceans, the monsoon seasonal'cycle causes the equatorial- undercurrent in the Indian
Ocean to be quite unique. The Equatorial Undercurrent (Cromwell Current in the Pacific,
Lomonosov Current in the Atlantic) is a thin, equatorially-trapped subsurface eastward jet
which traverses the entire basin beneath a strong, westward surface flow. It is a persistent
feature in the Atlantic and Pacific Oceans, but has been observed only in the boreal-spring
in the Indian Ocean. However, -like many other phenomena in the tropical Indian Ocean-
the data is sparse. Observations have reported westward subsurface currents during the
southwest monsoon, and a highly baroclinic structure, but the seasonal cycle of the
subsurface structure is not well understood.
The goal of this study is to describe the seasonalcycle of the tropical-Indian Ocean in
the SCM, and to compare the model with observations. There are two significant results
which may come out of such an analysis. The first is-to-demonstrate the-credibility of the
4
model (and to determine weaknesses which need to be improved in further studies). The
second result is that the ocean may-be studied systematically, gaining insight into processes
at work which have escaped limited observational resources.
5
II. THE MODEL
The progress of numerical-modeling, like so many other technologies, has been largely
evolutionary, with small improvements added to refine existing model codes, in between
major-revolutionary steps associated with new computer-architectures. This-study falls into
the former category; the difference between this study and the model described by Semtner
and Chervin (1988) is that monthly wind forcing isincorporated, instead of an annual mean
forcing. The SCM code is a primitive equation, robust-diagnostic global ocean circulation
model with 20 vertical levels -and 1/20 by 1/20 degree horizontal resolution, covering a
domain from 75'S to 65°N. The model is based on the Bryan-Cox model code (Bryan and-
Cox,1968), revised to allow arbitrary bathymetry and-coastlines -(Bryan, 1969), updated
for vector processing (Semtner, 1974) and for supercomputers employing parallel
processors (Semtner and Chervin, 1988). Figure 2.1 illustrates-the major general ocean
circulation development efforts which led up to this model. Further details of the historical
progression of global-ocean modeling are given in Semtner (1986a).
TABLE 2.1. EXPERIMENTAL SEQUENCE, AFTER SEMTNER ANDCHERVIN (1988).
-Restoring-Time Constant
Phase Integration Wind Horizontal 25-710 m :Deep OceanPeriod, years -Forcing -Mixing
1 0-4 Annual mean Laplacian: 1 year 1 year2 4-10 Annual mean Laplacian 3 years -3 years3 10-18 Annual mean Laplacian -none 3-years4 -18-22.5 Annual mean- -biharmonic 'none 3 -years5 22.5-32.5- -Monthly biharmonic none 3 years -
This study is part of a 32.5-year simulation of the global ocean circulation. The paper
deals with the results of Phase 5 of the experiment, as listed in Table 2.1. Phases 1-4 were
reported by Semtner and Chervin (1988). Since this paper is dealing with the monthly
6
wind forcing, the year numbers referred to in this-paper will apply only to Phase5 (Year 1
is the first year of-simulated monthly forcing).
The wind stress used in the model comes from the Hellerman and Rosenstein (1983)
global data-set. These wind-stress values,.defined on a grid with 2- spacing, have been
interpolated-to tie 1/20-surface velocity grid-points of the model. While Phases 1 through 4
used annual mean Hellerman and Rosenstein wind stress, in Phase 5, the data base-was
partitioned into mean monthly values. A smooth curve was fit to these monthly values, and-
divided into daily increments. During-the integration, the wind stress is held constant over
a-three day period, at the end of which model results are archived; and-a new value of wind
stress is selected. Over a three-year period, each daily wind-stress value is-used once, and
applied for three days. While the wind stress in Phase 5 has seasonal variability, it has no
interannual variability. It will be shown that this lack of interannual variablity leads to
some features in-the model climatology which deviate from observational climatology.
However, the non-linear characteristics of the model give it an inherent (but small)
interannual variability.
Temperature and salinity fluxes at the surface have been parameterized by forcing the
surface grid-points to monthly mean Levitus (1982) values on a monthly time scale, after
the method of Haney (1971). In Phase 5, the heat and salt budgets are unconstrained
between 25-and 710 m, while the deep layers are restored to Levitus values on a 3-year
time scale. The only Levitus forcing that occurs within the thermocline is from 55 0-65 0N,
and from 65 0-750 S, where T and S are restored to Levitus (1982) on a 3-year time scale. In
this robust-diagnostic, free-thermocline strategy (Sarmiento and Bryan, 1982) , the top
layer is forced with wind stress on the momentum grid points and with Levitus forcing on
the TS points, while the seasonal thermocline is completely free over most of the domain.
7
Since-the 30 years of this study is short compared with the-millenium time-scale of the deep
ocean, the deep layers are weakly restored to Levitus values to constrain any drift.
The 20 vertical-levels in-the model are-stacked downward, with the4ocal bathymetry
defined- by the-number of boxes. The levels are-unevenly spaced, with 10 levels in-the
upper 710 m to resolve the-thermocline. Figure 2.2 illustrates the vertical arrangement of
levels in the model. The spatial averaging of bathymetry required by the grid size-and some
simplificationsin geometry have resulted in an idealized model ocean (Figure 2.3). The
Red Sea, the Gulf of Aden, the Persian Gulf, the Gulf of Oman, the Andaman Sea, and the
Great Bight of Australia have been filled in. In order to simplify -calculations of the mass
transport streamfunction (Semtner, -1986b), some-major islands-have been connected-to
continental land masses: Madagascar has been connected to Africa -by filling in the
Mozambique Channel-. Sumatra, Java, and-Bomeo have been incorporated into a larger,
simplified southeast Asian peninsula, and the islands of New Guinea and Tasmania have
been connected to Australia. Other islands, such-as Ceylon, Socotra, and the Seychelles,
have been shoaled to-a depth of 100 m (then subjected-to.nine-point smoothing), which
allows their major bathymetric features to remain in place, yet eliminates-the numerical need
to perform a line integration around these islands (Semtner, 1986b). The bathymetry of the
model is-shown in Figure 2.4. While performing line integrations around every island-is
possible, it was considered to be too inefficient -to include every island in this global
circulation study. The incorporation of the free-surface effect by-Killwonh etal. (1990)
requires no such line integration, and the use of an arbitrary number of islands without
such computational penalty is now possible.
Although the geography has been simplified, the Indian Ocean is not constrained by
any regional boundary-conditions. It-is free to exchange momentum, heat, and salt with the
other parts of the world ocean, which are being simulated simultaneously. The transport-of
8
warm water from the western Pacific Ocean through-the Indonesian Archipelago, across the
Indian Ocean, and into the Atlantic Ocean v ia Agulhas rings-has been described for thu
annual forcing phases of the simulationby Semtner and Chervin (1988).
Other-features of the model include a Richardson Number-dependent parameterization
of verticalmixing after the-method of Pacanowski and Philander (1981), and biharmonic
parameterization of frictional and diffusive properties. The explicit -treatment of eddies
allows the amount of mixing carried out by parameterization of sub-grid scale processes to
be minimized. The eddies perform the bulk of *he work of mixing momentum, salt, and
heat,- leading to a fairly realistic representation of the-global circulation.
9
IlL WIND STRESS
Itis important to understand the dynamics of the Indian Ocean in-terms of seasonal-
variation in the wind stress; this-section will review the-annual cyc:--of Hellernan-and_Rosenstein (1983) wind stress in the-tropcal Indian Ocean- of the global model. The
monthly mean wind-stress, which was-used- to force Phase 5 of the experiment, is shown-
in Figures 3.1-3.6. The predominant feature is the wind stress due to the southeasterly
trade winds. The SE trades are very constant in- azimuth throughout the year, withsigaificant variation only in magnitude and latitudinal-extent. The other major feature of the
mean- forcing is the southwesterly winds in the western Arabian Sea-and the Bay of Bengal.
These areas, however, have a-large seasonal variat dity in both azimuth and magnitude, and
it is this monsoon which is associated with the :rajor oceaicieculation changes in the
Indian Ocean.
In January (Figure 3.1 (a)), northeasterly flow is prevalent -in -the Indian Ocean and
Arabian Sea in the Northern Hemisphere, known as :the Northeast Monsoon. The
northeasterly flow extends to approximately 10'S in the western Indian Ocean near
Madagascar. South of 100S, the -winds are from ESE in the western Indian Ocean,
becoming southeasterly- in the eastern Indian Ocean. These are- the southeasterly tuadC
winds. From 631E to the eastern part of a.-. T-hdian OceaA, -there -is- a band of westerlies
with a-latitudinal extent of 50, located slightly south o, .e-equator. This band of westerlies
and the southeasterly trades converge to form the .. :ertropical Convergence Zone (ITCZ) at
10'S. The maximum wind stress is approximately 1.3 dyn cm-2 , located off of the Somali
Coast. Ir february (Figure 3.1(b)) the flow is virtually identical to January, with flow
weakening in the eastern Indian Ocean.
10
= _ =
In March, the flow is weakened in the westerr indian Ocean, with the wind stress
having decreased to less than 1 dyn-cm -2 , as illustrated in Figure 3.2(a). The highest-wind
stresses are-due to -the SE trades in the easte,- 'dhdian Ocean. In the western Arabian Sea,
the winds have veered, blowing-towards thv C. - Aden (toward the western boundary in
the model), while the flow is north,,., ',_ r.' :e .,ral Arabian Sea as part of a large
anticyclonic flow. The climatology shows an - zicyclone centered at 15"N, 870E in the Bay
of Bengal.
By April-(Figure 3.2(b)) the SE tr-ades hb ,e ,ecome :tronger, penetrating as far north
as the Equator in the Western Indian Ocean. The maximum wind stress is approximately
1.5 dyn cm-2 , and- the SE trades extend further to the east. There is a southeastckrly
onshore flow over the Kenya -/Somali coast, and-the -wind stress- is very weak in the
western Arabian Sea. A weak anticyclone is present in-the central Arabian Sea, resulting in
northwesterly winds alongshore-at the Indian coast. The anticyclonic ciculation in the Bay
of Bengal has resulted in a reversal of the directioi. of the winI stress since January. The
ITCZ (not shown) has shifted ..,rth, and the band of equatorial westerlies has also-shifted
north, with its direction- changing from V,'TNW to WSW. The -band of westerly winds -has
also increased its latitudinal width to 100 (i.e., between 100S and the equator).
May is a transition month from- the NE-to SW monsoon regime. Figure 3.3(a) shows
that the cross-equatorial flow is much stronger. The SE trades- extend -to .he-equator, then
become southwesterly. The southerly onshore flow at the Kenyan coast has increased in
magnitude. The weak anticyclonic flows of April in the Arabian Sea and Bay of Bengal
have been replaced by a strong westerly anticyclonic flow in the Arabian Sea, and a strong
westerly cyclonic flow in the Bay .,: Bengal. The wind stress in the western Arabian Sea
has completed a 1800 shift since March and increased-its amplitude-to a n, ximurr. A' 1.3
11
dynfcm-2. The-winds in the western Indian Ocean-have-attained the-basic-pattern that they
will retain throughout the oncoming SW monsoonseason.
in June, the circulation pattern established in-May-picks up tremerdous strength -with
the onset of the SIX Monsoon, as depicted in Figure 3.3(b). Wind stresses in ,he western
Indian Ocear have increased 2-3-dyn cm-2. The onshore flow in India and soi.,heast Asia
has become much stronger. The wind ,tress in the western Indian Ocean approaches
4 dyn cn -2. The :E trades tLr,. and become SW at the equatorHi, the western Indian
Ocean, and at 20S in-the eastern Indian Ocean.
July (Figure 3.4(a))- is the month of the largest wind stress valv e of the SW
Monsoon. Hellerman and:Rosensttin:(1983) reported-that the highest wind stress in the
106-year global data set occurs-ir, the western-Indian Ocean. The wind stress at -100N/530E
is 4.9 dyn cm -2. The great intensity of the winds in this region is due to the Finlater Jet
(Finlater, 1969), which causes intensification of the southerly-wind flowing onshore over
Kenya and Somalia. The wind stress in the western Indian Ocean has a typical increase of
1 dyn cm-2 from June to July.
The SE trades-in the western Indian Ocean continue to increase in magnitu,.' luring
August (Figure 3.4(b)), creating wind stresses of nearly 2 dyn cm- 2. In contrast, the
sout' ,wc sterly monsoon winds in the northwest Indian Ocean decrease, reducing wind
stressfs-there by 0.5-1 dyn cm-2 .
Septemlxr (Figure 3.5(a)) brings further weakening of the SW Monsoon, with wind
stress levels decreasing by 1-2 d, n cmi2 . The climatological wind stress magnitudes in
September are oniy 0.5-1 dyn cm 2 greater than the levels in-May, indicating that the SW
Monsoon season is nearly over.
The October wind stress plot (Figure 3.5(b)), shows a pattern of weak wind stress-in
the northern Indian Ocean, indicative of transition to the NE monsoon season. While the
12
Arabian-Sea experienced-a large scale anticyclonic circulation in-September, the anticyclonic
flow is now weak in the western Arabian-Sea, while the flow in-the eastern Arabian Sea is
cyclonic. Although the Bay of Bengal wind stress pattern indicates that cyclonic winds
remain, the magnitude is small and there is no Burmese onshore flow as seen in
September. The SE trades have typical alues of 1.5 dyn cm-2, weakening from the
September values.
The November climatological wind stress plot (Figure 3.6(a)) illustrates that the
transition to the NE Monsoon regime is complete- Northeasterly flow dominates the Bay
of Bengal and the Arabian Sea, resulting in wiihd stresses less than 1 dyn cm-2 . The
weakening SE trades have shifted to .n east -_d the equatorial westerly pattern is weaker.
The December plot of wind str .ss -(Figure 3.6(b)) is very similar to the pattern of
January. There is an increase in wind stress strength to 1 dyn cm - 2, and the belt of
westerlies has shifted south of the Equator.
13
IV. RESULTS
A. NEAR-SURFACE CURRENTS
1. The Seasonal Cycle
In this section, plots of the monthly mean current vectors will-be discussed. The
monthly mean- currents are chosen to illustrate the seasonal cycle-of the SCM in the-Indian
Ocean, forced-by the Hellerman: andRosenstein-(1983) winds. Before the monthly mean
currents are reviewed, several points-should be emphasized. First-,the lack of interannual
variability in the wind stress -causes the monthly mean currents :(and many other mean
fields) to be ve~ similar from year to-year. However, the eddy fields do vary considerably
from year to year, as illustrated by Figure 4.1. Figure 4.1-(a) shows the instantaneous
vector field at37.5 m in the western- Indian Ocean on January 15 of Year 4,-and-Figure
4.1 (b) shows the same field on January 16 of Year 5 (January 15 was not archived that
year). The eddy activity of the model-is the most striking feature of these plots, and-there is
considerable variation in the eddy fields between the two years -shown. In-the monthly
mean vector plots (January of Year 4 is shown-in Figure 4.2; Year 5 is not-shown), the
averaging of the eddies creates a "patchiness", and the geostrophic currents are the
dominant feature. While differences can be seen-in the monthly meanwvector plots from
year to year, the changes are minor, and the Year 4 monthly mean plots presented below
are considered-to be a representative sample of the multiple year simulation. Figure 4.1
also illustrates that, as expected, the instantaneous currents throughout the basin are more
vigorous than the mean flows depicted below.
The monthly mean near-surface (37.5 m depth) geostrophic currents in the
Indian Ocean basin of Year 4 of the simulation are shown in Figures 4.2-4.13. (Since the
14
upper grid-boxes are 25 m thick each, the:Ekman effects are largely confined-to the top
layer (not shown)). In January, Figure 4.2 shows -the South Equatorial Current (SEC)
flowing westward at approximately 15S in response to-the forcing of the SE trades. It
turns south-at the east coast of Africa to feed the Agulhas Current, and north to feed the
Equatorial Countercurrent (ECC). The-NE Monsoon forces the westward-flowing North
Equatorial Current (NEC) from 20 S to-80N. It turns-south at-the African coast-to join the
SEC, becoming source waters for the ECC. The NE Monsoon turns at-the equator to form
a band-of equatorial westerlies, which provide the continued forcing for the ECC as -it
transits-the entire basin between 3'S and 70S.
In February (Figure 4.3), the NEC attains its greatest strength, achieving
westward velocities as high as-68 cm s-1. By March (Figure-4.4)i with-the reduced wind
stress from the waning NE Monsoon, velocities are reduced throughout the NEC, the
reduced wind stress in the eastern Indian Ocean causes the NEC to retreat to the west. As
the NEC weakens, the ECC becomes- more concentrated as its-southern bound moves-from
7'S to 5S in response to the south equatorial westerly trades shifting farther-to the north.
In April (Figure 4.5), although westward-wind stress is no longer available to
drive the NEC, the NEC-continues to exist as a weak westward countercurrent south of
India throughout the SW monsoon. The ECC in April becomes a meandering flow
between 5S and the equator in the western Indian Ocean, splitting into two jets at 750E.
One jet-remains at the equator, in the region of eastward wind stress where the Wyrtki jet
forms in May, and the other at 5°S, in the region of-the doldrums between the.SE trades
and the equatorial westerlies. This branching of the eastward flow south-of the equator
persists throughout the southwest monsoon period until the ECC is re-established in
December. The eastward flow at 50S, characterized-as the ECC during the NE monsoon,
remains a distinct jet during the SW monsoon, however, during the SW monsoon period it
15
is no longer a countercurrent, and is considered part of the SW Monsoon Current. The
southwesterly flow along the Somali coast hasrminimal velocities in April, as expected in a
region of weak-wind stress.
The -rapid -onset of the SW Monsoon in late May causes the climatological
monthly mean wind stress in May to be-northeastward along the Somali coast, resulting in
a-reversal of the Somali-Current (Figure-4.6). The eastward flow has formed an equatorial
surface jet (Wyrtki jet), and is confined between-3*N and 3S. The core of the jet attains an
eastward-velocity in excess of lm/s between 60'E and 800E. A weak eastwardcirculation
remains in the equatorial trough at 5S.
By June, the-eastward-flowing SW Monsoon Current (SMC) is established at
50N (Figure 4.7). Increased solar insolation in the Northern Hemisphere causes the ITCZ
to move northward in the summer hemisphere, and the equatorial trough in the winter
hemisphere moves equatorward. As-a result, the region of maximum eastward wind stress
migrates northward, and-the doldrums move closer to the equator. Although the eastward
component-of wind stress at the equator has increased to the west of 60°E, ivdecreases
between 60 0E and 80'E, as shown in Figure 3.3. This results in a- weakening of -the
equatorial jet, which reached a maximum in May, and-the subsequent intensification of the
SMC. The Somali Current has strengthened under the increased wind stress, forming a
western boundary current which extends as a strong jet to 80N, where it recirculates
southward to feed the SMC and the equatorial surface jet. The current recirculates
southward in several sections, with branching at 40, 60, and 80N. The branch at-40 N forms
part of an anticyclonic gyre, extending to the Equator, known as-the Southern Gyre.
In July (Figure 4.8)-there is continued weakening of the equatorial surface-jet,
and strengthening-of the SMC. The former equatorial surface jet has moved south into-the
doldrums, while a westward countercurrent has developed at 20N, between the two
16
eastward currents. The appearance of the-countercurrent is due-to surfacing of a westvard
deep level current (the deeper currents will be discussed separately in sections B and C of
this chapter). Under the influence of continued strengthening zonal wind stress, the SMC
no longer branches off from the equatorial jet, but is fed from the Somali Current
recirculation, and becomes visible as a distinct jet atapproximately 70'E. Its greatest
strength occurs at 82'E, where the core of the jet- attains a velocity of 80 cm s-l In-the
month of the highest wind stress in the-western Indian Ocean, the Somali Current also
reaches its highest velocity of 201 cm s. The Somali Current continues to be a one-gyre
system, with the Southern Gyre centered at approximately 31N. The broad offshore
branching of the Somali Current extends from 40N-to 12°N. Despite the strong wind stress
throughout the Arabian Sea-and the Bay of Bengal, the-circulation in these basins remains
generally weak.
By August (Figure 4.9) the broad northern segment of the Somali Current
offshore flow-has developed into a-second gyre. This northern gyre, known as the Great
Whirl, is centered at 100N, while the Southern Gyre remains centered at 30 N. The-fornier
equatorial surface jet may again be referred to as the Equatorial Countercurrent,-since-it is
again flowing eastward, at 3S, in an opposi~e direction-to the zonal wind stress throughout
most of the basin. The SMC has weakened in its peak intensity in response to the-reduced
Sind stress during August, yet it becomes og~anized into a coherent-jet slightly farther to
the west, at 65"E. The transitory westward countercurrent which appeared in July at 20N is
no longer visible at the 37.5 m level.
Increased equatorial zonal wind stress in the eastern Indian Ocean in September
results in a southern branching of the SMC, forming a jet just to the north of the equator
(Figure 4.10). Thisjet peaks at 76 cm s-1 atalongitude of 870E. As the equatorial trough
moves southward, this jet will reform the Wyrtki surface equatorial jet. The ECC is
17
present in the doldrums at 40 S, extending across most of the ocean basin. In the Somali
Cunent region, the Great Whirl has moved northward to-12°N, while the Southern Gyre
has developedinto two-anticyclonic circulations. One of these gyres is centered at 3°N, at
the August position of the Southern Gyre, and the other one has -formed at 6'N from the
broad offshore flow of the Southern Gyre. An anticyclonic gyre has formed to the
northeast of the Great Whirl, at 13'N/580E. This gyre is-the model analog of the Socotra
Eddy.
In October (Figure 4.11), with alongshore transport by the Somali Current
greatly diminished, the zonal currents in the western Indian Ocean are more clearly
organized. October, like May, is a month of relative maximum wind stress at the equator
The Wyrtkijet-no longer appears as a southern branching of the SW Monsoon Current, but
is a continuous -zonal jet from the Somali Current region to the eastern end of the basin. It
attains a maximum velocity of 81 cm s-I at 849E, with-the core- of the jet at I°N. This
corresponds to- the region of highest zonal wind stress. The Great Whirl is located at
12'N, while the two gyres to the south are located at 4'N and 70N. These-southern gyres
are substantially weaker than they were in September.
In November (Figure 4.12), there are two anticyclonic gyres visible at 100N-and
140N, which are remnants of the Great Whirl and the Socotra Eddy. The zonal current at
the equator attains a semiannual maximum in November, as the Wyrtki jet is centered on
the equator. It attains amaximum velocity-of 75 cm s-1 at 830E.
During December (Figure 4.13) the Great Whirl continues to diminish, the
surface equatorial jet loses strength, and the ECC reorganizes. As a result, the model
Indian Ocean circulation returns to the basic pattern it had-in January (Figure 4.2).
18
2. The Wyrtki Jet
As first described by ,iyrtld (1973), a semiannual surface equatorial jet appears
in the Indian Ocean during periods-of maximum zonal wind stress. This relationship can-
be clearly seen in the longitude-time plots of Figure 4.14. Figure 4.14-(a) shows relative
maxima in the magnitude and zonal extent of the zonal wind stress in the months of May
and October, related to the seasonal migration-of the ITCZ. (Another zonal-maximum is
visible in the western Indian Ocean in June and July, related to the Finlater Jet.) Figure
4.14 (b) shows the vertical integral-of the zonal current at the equator in-the top two levels
of the model (12.5 and 37.5-m). It shows eastward currents with maxima in May and-
November, in response-to the periods of maximum zonal wind stress.
Figure 4.15 (Reverdin (1987), after-Cutler and:Swallow (1984)) shows that
observations of zonal equatorial currents, derived from ship drift reports in the Indian,
Ocean, show equal strengths of the two Wyrtki Jets (the time scale is reversed from that
presented in Figure 4.14), whereas the SCM has the May jet (113 cm s-1) stronger than the
November jet (72 cm s-1). Similar results have been obtained in the Geopyhysical Fluid
Dynamics Laboratory (GFDL) of Princeton University regional simulation of the Indian
Ocean, which also uses Hellerman and Rosenstein (1983) winds. (F. Schott, personal
communication). (Figure 4.15 also shows the good agreement of the strength of the
model NEC (68 cm s- 1) with the ship drift reports (>60 cm s-1 ). Overall, as shown in%
Figures 4.14 and 4.15, there-is good agreement in ,ne timing and strcngth of the:SCM
surface equatorial currents with observations.)
B. THE EQUATORIAL UNDERCURRENT
The subsurface velocity structure in the tropical Indian Ocean has not been well-
sampled spatially or temporally. Studies of the area have shown a great-deal of variability
and a high degree of baroclinicity in the subsurface flow. Due to the variability of the
19
monsoon-forcing,-the-Equatorial Undercurrent (EUC)-in the Indian:Ocean displays much
more variability than its counterparts, the Cromwell Current and-the Lomonosov Current in
the Pacific and Atlantic oceans,-respectively. The "equatorial undercurrents" are described
as thin, equatorially-trapped eastward jets, which are:located beneath strong, westward-
flowing equatorial surface flows. The eastward-flowing EUC has been observed to exist
in the Indian Ocean during January through April, extending from 500E to 900E.
Khanaichenko (1974)-cites mass transports ranging from- 11 to 40 Sv, with a mean of
26 Sv.
The SCM Year 4 zonal-current velocity at-the equator was averaged between 117.5 and
160 m depth, and its longitude-time dependence is shown-in Figure 4.16. The eastward
EUC is visible from January to April, attaining a-peak zonal velocity of 62 cm s-1 at 800E
during March. Kort (1977) reported that observations of the EUC at 64.5°E revealed a
peak velocity-of 64 cm-s-1 at 100 m depth on 18 March, 1974, while the SCM output on
the tape archived-at 19 March of Year 4 shows a peak at 57cm s-1 at a depth of 117 m.
Mass transports of-the EUC-at 80'E in Year 4 range from 19-31 Sv. Leetmaa and Stommel
(1980) took measurements of the EUC at 55.5'E, and found-that at the end of the northeast
monsoon, the EUC shifts southward -to merge with the ECC; in contrast, the SCM shows
that the EUC moves upward and merges with the northward-migrating ECC.
A period of westward velocities is seen in Figure 4.16 during the months -of June
through August. Several authors have reported westward velocities-at this level during the
southwest monsoon, including the studies of Knox (1976), Luyten and Swallow(1976),
Luyten (1981,1982), Polonskiy and Shapiro (1983), Ponte and Luyten (1990). Knox
(1976) reported that the westward undercurrent was observed following the semiannual
eastward Wyrtki jets, as a possible relaxation of water "piled up" in the eastern basin by the
Wyrtki jets. The SCM shows a westward undercurrent following only the May Wyrtki Jet.
20
One possible-reason that the model shows only one period of-the westward undercurrent is
because the SCM Wyrtki jet-in November is much weaker than the May jet (Figure 4.14)
while the ship drift observations (Figure 4.-15) indicate Wyrtkijets of equal-strength.
The seasonal cycle of the vertical structure of-the-zonal currents at the equatorduring
Year 4 is shown in Figures 4.17-4.28. Figures 4.17-4.22 show the zonal current velocity
along the equator from 0-610 m, while Figures 4.23-4.28 illustrate the zonal currents in a
cross section at 80'E, from 20'S-200N. The time sequence of Figures 4.17-4.22 shows the
eastward-EUC beneath the NEC during the SE Monsoon, and merging of the EUC with-the
Wyrtki jet in April (Figure 4.18 -(b)) and May (Figure 4.19(a)). The westward
undercurrent-is shown during the boreal summer, and the semiannual Wyrtki jet is-visible
again in October (Figure 4.21 (b)). Figures 4.23-4.28 illustrate the same features of the
seasonal cycle, yet show off-equatorial features as well. The appearance of the westward
countercurrent at 3'N in July (Figure 4.26 (a)) is shown to be a surfacing of the westward
undercurrent. The synoptic structure throughout the basin can be seen in Figures 4.29 and
4.30, which show meridional sections at- 60°E, 701E, 80'E, and 90'E for the months of
February and July in Year 4. Leetmaa and Stommel (1980) studied the-EUC at 55.50 E, and
found that at the end of the northeast monsoon, the EUC shifts southward to-merge with
the ECC, but the SCM shows the EUC moves upward and merges with the Wyrtki jet (see
Page 20-also). Figure 4.31 is a vector plot of the instantaneous currents at 117.5 m,
archived on March 10 of Year 4. It clearly shows the EUC spanning the entire basin, and
the eddy-resolving nature of the model is apparent. The eastward flow of the ECC can be
seen to the south of the EUC.
C. DEEP CURRENTS
The seasonal variability of the EUC and baroclinic structure of the equatorial Indian
Ocean, along with a sparse set of observations, have made it very difficult for
21
oceanographers to come up with a comprehensive picture of the flow in-even the shallowest
subsurface layers. The model exhibits the same type-of complex-vertical structure-that the
observations (Knox (1976), Luyten and Swallow(1976), Luyten- (1981,1982), Polonskiy
and Shapiro (1983), Ponte and Luyten (1990)) suggest, as shown in Figure 4.32, a-cross
section from 30S to 3'N. Taken in March, when the EUC is at its peak strength, the plot
indicates cores of westward flow near the surface and at 435 m depth, while separate
eastward--cores are visible at 117 m, 1160 m, and 3575 m depth. Analysis of time
sequences of zonal current-plots indicate that an upward phase-propagation of the zonal
currents takes place in the equatorial region. However, O'Neill and Luyten (1984) reported
that acoustic dropsonde observations of the equatorial Indian Ocean at 530 E-do not yield
evidence-of vertical phase propagation-of the -zonal currents. McCreary (1987) reported
model results which suggested that the interaction between deep mean currents and near-
resonant Kelvin waves can account for much of the observed deep jet structure without
vertical phase propagation. However, the theory of deep jet dynamics remains incomplete;
McCreary (1987) reported that while the model reproduced-the deep current structure well,
the near-surface flux field was unrealistic. Further observational and theoretical work is
required -to suggest changes to the SCM which would more accurately represent the
dynamics-of the deep jet structure.
The-currents at 4125 m during June of Year 4 are illustrated in.Figure 4.33. The
model domain at this-level shows the various deep basins in the Indian Ocean: the Arabian
Basin, the Somali/Mascarene Basin, and the Madagascar Basin in the western Indian
Ocean, and the Mid-Indian Basin and Wharton Basin, separated by the-Ninety East Ridge.
A series of deep eddies are visible, as is the tendency of the currents to form western
boundary currents. A series of strong, anomalous currents-is seen at -pproximately 1230E,
in the Celebes Sea, where anomalous data in the Levitus (1982) data base was revealed by
22
the model. The temperatures at this depth are 5-10'C too-high, causing the model to-
respond to the anomalous gradients -by creating currents which are too strong. (This
example of the model revealing bad data in-the Levitus data base suggests that the model-
may be able topoint out more subtle deficiencies in the global observational data bases.)
The complexity of the subsurface currents in the Indian Ocean is further demonstrated-
in-Figure 4.34, illustrating the-longitude-time dependence of the zonal velocity at 435 m
depth. This figure shows a pattern of convergence and divergence, which travels
westward at approximately 25-35 cm-s-1. This pattern-of convergence and divergence is
visible also in Figure 4.35, a plot of monthly mean-current vectors at the 435 m-level-
during March of Year 4. The westward movement suggests-another interpretation to the
upward phase propagation of the-zonal velocity in-the-model. Figures 4.17-4.22 show that
the zonal jets tilt upward from west to east; westward propagation of such a tilted feature
would also create an upward phase propagation at- a fixed point on the equator. The source
of the tilt of the jets in the:model is unclear, it is not visible in the deep thermal structure,
which suggests that the distribution of vertical velocity may play a role.
D. THE LEEUWIN CURRENT
The western coast of Australia is-another unique region of the Indian Ocean. While
most eastern boundary surface currents are the equatorward portions of the subtropical
gyres, the Leeuwin Current is a poleward-flowing (southward) eastern boundary current.
The poleward Leeuwin Current forms in the austral autumn and winter, flowing along the
edge of the continental shelf, eventually extending- around the Great Australian Bight. The
Leeuwin Current has only-recently been documented, in part because it is a very narrow
current, sometimes less than 30 km wide. The Leeuwin Current is also quite notable for
moving at significant speeds (maximum approximately 1.8 m s-1), in opposition to the
prevailing wind stress. Recent observational, modeling, and theoretical studies of the
23
Leeuwin. Current have been summarized in Church et al. (1989) and- Weaver and-
Middleton (1989). The~prevailing theory, as espouseO by Thompson (1984) and-Godfrey
and Ridgway (1-985), is that the Leeuwin Current is driven by large alongshore steric
height gradients. Weaver and Middleton (1999) and Batteen and Rutherford--(1990)-
demonstrated that the Leeuwin Current could be modeled-by primitive equation models,
using climatological winds, and without resolution of the-continental shelf. Since these
modeling studies employed much finer horizontal grid resolution than-the SCM, the-ability
of-the model to resolve Leeuwin Current features was-a matter of some interest. Although
the SCM: cannot resolve the Leeuwin- Current to the-level of the observations and local
modeling studies, it does demonstrate many of the seasonal features of the Leeuwin
Current. However, the-current-is marginally resolved, and: suggests that operation of the
model at 1/40 horizontal resolution will result in a-more- accurate representation- of the
structure of the Leeu win-Current.
The monthly (Year 4 data) averaged vector and temperature plots of Figures 4.36
through 4.47 illustrate- the seasOnal cycle of the Leeuwin Current. The vector plots show
eastward-geostrophic currents, turning poleward at the Australian continental shelf. During
the austral summer, the eastward flow turns poleward:when itmeets-the shelf at 29°-31°S.
Church et al. (1989) describes it as a northeastward flow, turning poleward near the shelf
at-290-31S. The Leeuwin Current is visible in austral-fall and winter, as the-eastward flow
turns poleward over a wider range of latitudes, and is augmented by strong-flow from the
northwest shelf. Figures 4.37-4.40 show the development of this southwest flow on the
northwest shelf from February to June. During the same period, the Leeuwin Current
progresses further around Cape Leeuwin each month, creating an eastward flow along the
southern Australian coast . The series of plots shows an eastward flow along the
northwest-shelf from July through December, as well as re-establishment of westward flow
24
along thesouthem coast of Australia. The pluts-of the traoperature field also show features
described by Churchet al.: high temperature (>250 C vaters spread south-of 20'S in
austral autumn and winter, and the Leeuwin Curren hol-ds-the SST at 320 S above 22°C
untilcafter June. However, the-plots do not show 20 0-22'C water carried north to 250 S in
summer as described by -Church et al., they show 22 0-23"C water at -this- latitude in
December, January, and February. Plots of the salinity field (not shown) also depict
features -described by Churh et al.: low salinity-(<35 psu) waters-spreading south of 20'S
in autumn and winter. Hcw ever, there-were differences-in the salinity fields as well. The
salinity at 320S in the mode! in June was 35.6; Church et al. describes winter salinity at
this-latitude as 32.2-32.4.
Additionally, cross sections were plotted to -simulate the Leeuwin Current
Interdisciplinary Experiment (LUCIE) sections depicted in the study of Church etal.
(1989). Sample comparisons-are shown in Figure 4.48 for-the Dongara (30'S) LUCIE
sections. Figure 4.41 (a) shows the LUCIE September 1986-February 1987 mean
alongshore currents for-the Dongara section, and Figure 4.48 (b) shows the corresponding
model section of v velocity during January, Year 4. The LUCIE current section depicts
mean southward flow (20 cm s-1) at the 300 m isobath, and mean northward flow of 15
cm s- 1 at 500 m. The model shows upper level southward flow of 5 cms -1, and a
northward flow of 9 cm s-1 at 310 m. The temperature fields of June are compared:in
Figures 4.48 (c) and (d). The model section shows downward bending of the isotherms
at the coast, but less intense than the LUCIE section. The 200 C isotherm matches well;
however, the 21'C isotherm does not.
E. SURFACE HEAT FLUX
One of the difficulties in designing a global ocean circulation model is that the
investigator must prescribe the heat flux consistently throughout the domain, in a manner
25
which is consistent with climatology. Unfortunately, there are no suitable global
climatologies of heat flux. The method used to parameterize surface-heat flux in the;SCM
-(Semtner and Chervin-(1988)) is adapted after the method of Haney (197 1). Rather than
explicitly prescribing either the-sea surface temperature or the surface heat-flux, a suitable
climatological temperature (in-this case the Levitus (1982) monthly:mean- temperature at
12.5 m for a given grid point)-is used-as a set point-in a negative feedback loop control
system. At each time step of the integration, if the model temperature is colder (warmer)
than climatology at a given point, then it is warmed (cooled) at a prescribed rate. The
Levitus (1982) data base was the only climatology suitable for this approach, because it is
global in scope, 4) ailable at multiple levels , and seasonal. The model incorporates a
forcing-term which applies this virtual heat flux ^oward the Levitus (1982) values on a
monthly time scale. The form of the term, applied t- the top -temperature grid- point (12.5
m) at every time step, is-approximately
T + TLevitus - TModel
at 30 days (1)
The parameterization of the complex heat budget by such a- simplified approach
warrants some investigation. Comparison of the Levitus surface thermal forcing with the
available regional climatologies of heat fluxes demonstrates that the Haney method
parameterizes the surface heat fluxes adequately in the Indian Ocean basin. Figure-4.49
illustrates the surface heat fluxes calculated from the Cooperative Ocean-Atmosphere Data
Set (COADS) by Rao et. al. (1989) for the months of January, April, July, and October.
Figure 4.51 shows the fluxes calculated in the Hastenrath and Lamb (1979) atlas for the
same months, and the model's surface heat flux-due toLevitus temperature forcing in Year
7 is portrayed in Figure 4.51. The model matches the Hastenrath and Lamb (1979)
climatology better than the Rao climatology. This may be due to the much longer time
26
spans of the Levitus (1982) data base (1900-1978) and the-National Climatic Center data
(1911-1970) from which. the-Hastenrath-and Lamb (1979) flux calculations were derived,
-compared with the COADS data (1950-1979) that-Rao et ai. (1989) used.
in general, the SCM heats and cools-the Indian- Ocean-in the-proper regions, although
the magnitudes of the heat flux show some variation from-the climatology. The-model
heats-the Arabian Sea-and Bay of Bengalfin April much less than-the heating-of the-ocean
depicted by the Climatologies. The model consistently shows strong heatingjust south of
Madagascar. One other area-where the model shows much stronger forcing than-in the
climatology is along the African coast in:July. The model-has a maximum heating of the
-ocean-of ever 450 w m-2 , while the-climatologies (with heavy spatial averaging and-sparse
sampling) only show up to 160 w m- 2 in this-area. The mean monthly plots of Figure
4.51 show the contrast between the complex heat flux allowed by- the model during a-given
month and the temporally/spatially-smoothed- climatologies. The Levitus -forcing also
illustrates the freedom that the-top level-of-the model has to depart from the-climatology.
The Levitus -forcing (Figure 4.52), when compared with plots of '.-rtical velocity
(Figure 4.52), allows us to quaiatively assess the effects of upw.iling and thermal
advection on the Levitusforcing. As an example, areas of strong heat flux into the-ocean
are visible in the Somali Current region -in July, while-strong upwelling is confined to a
smaller region along the Somali Coast. The advection-of the cold, Ipwelled water accounts
for the remaining area of strong heat flux into the Arabian Sea. During the months of
December through April, the maximum itensity of surface thermal forcing in the model is
at the southern coast of Madagascar; this "cold spot" is a numerical artifact due to
divergence, and illustrates that the heat flux maps, combined with upwelling and advection
assessments, may be used to-help identify such anomalies in the model.
27
F. THE SOMALI CURRENT SYSTEM
The Somali Current forms a two-gyre system in the model, as described- previously.
A series of instantaneous plots of the Somali Current-at 37.5-m is-shown in Figure 4.53.
This series, covering the period from June 2 through August 16 of Year 4, shows how the
Southern Gyre is formed at-approximately 2-3'N, and remains-there, while the-Great Whirl
is centered-at 80N-on July 14, and has moved north to 100 by August 16. The Great-Whirl
continues to move northward, but moves farther northward than shown by observations,
because of the bathymetric simplifications of the model (J. O'Brien, personal
communication). The-island of Socotra has been-shoaled, and the Gulf of Aden filled in,
which both play an important role by the time the Great Whirl passes Cape Guardafui at the
tip of Somalia. Figure 4.54 illustrates the classical connection between the wind stress
along -the Somali coast, surface currents turning offshore, upwelling, and associated cold
temperatures. The upwelled temperatures are-as cold as 14'C in the-mean monthly plots.
The lack of interannual-variability in the Hellerman-and Rosenstein (1983) wind stress
creates a Somali Current gyre system which4forms in a consistentvmanner throughout the
simulation, while observations have noted considerable variation in the-development and
propagation of the two-gyre system, due to variability in the winds-from-year to year. The
lack of interannual variability in the wind forcing in the-model leads to a lack of temporal
and spatial variability-in the upwelling regions along the Somali coast. Hence, along the
east African coast during the summer, the model climatology-has colder temperatures than
indicated in the climatological fields. Furthermore, as reported- by Jensen (1989), the
forcing of the Somali Current by Hellerman and Rosenstein (1983) wind stress results in
the less-common-situation where the Southern Gyre does not move northward and coalesce
with the Great Whirl. Simulations of the more common situation where the two gyres
coalesce have been performed by Luther and O'Brien (1985), using seasonal wind stress
28
derived from the National Climate-Center Global-Marine Sums (TD-9757) data set, -which
has climatological winds on a 1 grid, instead of the 2' _grid-of the Hellerman and
Rosenstein (1983) wind stress used by the Semtner and Chervin model. Luther and
O'Brien's (1989) continuous-interannual simulation of the Indian Ocean, which used-Cadet
and Diehl's (1984) 23-year series of observed winds, was divided into 14 years where the
two gyres coalesced, 7 years where the Southern Gyredid not move to the north, and 2
years without a two-gyre system. The output-of the Semtner and Chervin model forced by
Hellerman and Rosenstein (1983) wind stress in the tropical Indian Ocean is encouraging,
and indicates thatthe model climatology may be made more realistic (particularly in the
Somali Current region) by incorporating interannual variability into -the wind stress.
Unfortunately, a suitable global set-of multiyear observations isnot yet available.
The Somali Current-in the model attains velocities as high as 2 m s-1, which are lower
than the highest observed currents of approximately 35 m s-I, although this should be
expected due to the climatological wind-stress and-the horizontal resolution of-the current.
One of the difficulties in analyzing the Somali Current of-the SCM is thatwthe software tools
do not allow sections to-be taken perpendicular to the coast; only zonal or meridionalcross-
sections may be used -to assess the Somali Current. It is common practice for the
observations to be taken in an alongshore/offshore plane, so direct comparison is difficult.
Quadfasel and Schott (1983) presented historical-surface current data at 5'N along the
Somali Coast (Figure 4.55); accompanying SCM values of mean monthly v velocity are
presented for comparison. Cross-sections of v were taken at 5*N/48°E-520E, and
maximum values-of the-prevailing-current tabulated for the monthly mean tapes of Year 4.
These values show strong similarity in the development of the strength of the Somali
Current in the model with averaged observations.
29
The Somali Current is known to extend barotropically to great depths during the SW
monsoon, yet a southward-flowingiundercurrent has been documented-during the spring
transition and in the late summer.(Leetmaa (1982),-Schott-and Quadfasel (1982), Quadfasel
and Schott (1983), Schott (1983)). During the northeast monsoon, there is no southward
under(counter)current, since the flow is southwestward at the-surface and at deeper-levels.
Cross-sections of v velocity-at 5'N and vector plots at various levels have been used to
analyze whether the SCM represents these subsurface flows correctly-along the step-like
model continental outline. Leetmaa et al.(1982) -presented cross-sections of alongshore
-flow at 5'N, as shown in Figure 4.56 (a) for 16-17 May 1979. A cross section- of v
velocity (50N/48 0-530 E) from the SCM monthly mean tape of May, Year 4 is presented for
comparison in-Figure 4.56 (b). Although the monthly mean currents in the model are
weaker, the structure is similar, and the southward-flowing undercurrent is present.at the
proper depth with the-core at the proper level. Plots similar to Figure 4:56 (b) indicate that
the SCM has southward flow at the surface during the months of November through
February, and -northward flow with deep southward undercurrents during March, April,
and May. The SCM-deep northward-flowing Somali Current-has no undercurrent from
June through August, but in September and-October a deep undercurrent-is present. Vector
plots give additional insight into the behavior of the undercurrent in the model. Year 4
instantaneous vector plots at 37.5 m, 222.5 m, and 435.0 m along the African coast are
presented in Figures 4.57, 4:58, and 4.59, depicting the flow on May 15. July 14, and
October 15, respectively. Obsei vations have reported that the undercurrent tends to turn
offshore between 3-5°N, while the undercurrents in the SCM show more complicated flow
patterns.
30
G. THROUGHFLOW IN THE INDONESIAN ARCHIPELAGO
A key testof any global ocean-model is its ability to accurately simulate the-interaction
between oceanbasins. Althouoh the SCM has some limitations-in this respect, such as thelack of interaction with the Arctic Ocean, it does allow flow between the Pacificand Indian
Oceans. The model domain includes a channel between the Asian continent and
Australia/New Guinea (Fig. 2.4). The SCM has submerged some islands, and
incorporated others-into the Asian-landmass, but-the Java Trench and adjacentcontinental
shelves do allow significant transport. A net transport from the Pacific Ocean into th!_
Indian Ocean is-known to occur through the Indonesian archipe!ago.
As Semtner and Chervin (1988) described,-the flow of warm Pacific waters into the
Indian Ocean through the Indonesian archipelago is vital to the heat transport across the
Indian Ocean and into th. Xtlantic. The mass transport into the.indian Ocean may play a
part in the flow of the SEC, West Australian Current, and inthe Leeuwin Current (Godfrey
and Goldin- (1981), Godfrey and Ridgway(c985),Kundu and McCreary (1986), Weaver
and Middleton (1989)). Interannual-variability inithe flow from the Pacific into the Indian
Ocean may be associated with the El Nifio Southern Oscillation ( Vhite et al. (1985),
Nicholls (1984)).
Despite the importance of the flow between the Pacific and Indian Oceans, the
throughflow and its interannual variabilit) have not been well-observed. Estimates inferred
from observations include 5 Sv by Fine (1985) and 8.5 Sv by Gordon (1986). Estimates
from numerical modeling studies range from 7 Sv, by Kindle et al. (1987), to Godfrey's
(1989) estimate of 16±4 Sv. Godfrey (1989) argued that the actual throughflow must Ix.
closer to 16 Sv than-to 0 Sv by modeling Indian Ocean steric heights with no throughflow,
and showing that the resulting steric height gradients show a much poorer match to
observations than the model output with 16 Sv throughflow. Semtner and Chervin (1988)
31
reported-a througlflow into-the Indian Ocean-of 15-18 Sv. The throughflow in the SCM
agrees well with the results-of the annual forcing phase of the experiment. Mean monthly
mass transport calculations at 117.5 0E from 5 years of the seasonal forcing are presented in
Table 4.1 . The mean annual westward throughflow is 17.74 Sv.
TABLE 4.1. MEAN WESTWARD MASS TRANSPORT IN THEINDONESIAN ARCHIPELAGO-
Net Westward StandardMonth Transport (Sv) Deviation -(Sv)January 15.96 .94February 18.74 .70March 20.66: .80April 21.28 .38May 18.20- 1.02June 18.64- .29July 17.72 .72August 16.08 .79September 16.72 .51October 16.94 .32November 16.22 .55December 15.70 .88
These results are illustrated in Figures 4.60 and 4.61. Figure 4.60 shows the monthly
mean westward, eastward, and net westward transport for the five-year time series. The
eastward and westward transports are highly correlated because strengthening of the
westward-flowing Pacific North Equatorial Current, which turns south at the western
boundary of the basin, results in strengthening of eastward-flowing countercurrents.
Furthermore, any eddies in the section will contribute equally to an increase in eastward
and westward flows. Figure 4.61 shows the five years of monthly net westward transport
overlaid on the mean net uvestward transport. The interannual variability of the monthly
mean mass transports in the-presence of interannually-invariant wind forcing is shown, and
the seasonal cycle of mass-transport is well-defined. Figure 4.62 shows the-bathymetry
and typical zonal transport across the sections at 117.5'E.
32
V. DISCUSSION AND CONCLUSIONS
A. MODEL TEMPERATURE VS. CLIMATOLOGY
If the goal of a model is to simulate the ocean as accurately as possible, then the-model
should exhibit a-realistic climatology. In the case of the SCM, the question is whether-the
inputs of the Levitus (T,S) and Hellerman and-Rosenstein (wind-stress) climatologies result
in a model which reproduces the Levitus (1982) climatology. For a complete analysis of
the SCM climatology, averages ofindividual months over-multiple years-are necessary, but
these products have not yet been compiled. However, the amount of inherent interannual
variability-of the SCM is small, andfthe fields contoured from January of one year look
very similar to January of any year, due to the lack of interannual variability in the
Hellerman and Rosenstein wind stress. As described previously, the eddy fields are
unique for each year, mixing heat, momentum, and salt, yet the mean monthly results are
quite similar from year to year Significant comparisons can be made between the SCM
mean monthly temperature plots and climatology. Comparisons of monthly mean 12.5 m T
in Year 7 are shown with the Hastenrath and Lamb (1979) sea surface -temperatures in
Figures 5.1-5.12.
Overall, the robust-diagnostic, free-thermocline strategy does not constrain the
Semtner and Chervin (1988) model so severely that it must diagnostically reproduce the
Levitus (1982) climatology of T (or S), but allows a prognostic solution in accordance with
the applied wind stress, where advection, upwelling, and the mixing effects of eddies may
dominate the solution at any given grid point. The primitive equation global ocean model
responds to the seasonal forcing with a realistic simulation of the circulation, and produces
33
a model climatology which is in good agreement with the historical data bases of
observations in the tropical Indian Ocean.
There are differences between the observed and model climatologies which illustrate
deficiencies not only in the model, but also in the climatological data base, both of which
must be overcome to enable long-term studies of climatic trends. The observations of the
Somali Current are inadequate, and result in temporal and spatial averaging of the
climatological data in the region which is inadequate for the intensity and interannual
variability of the current. The lack of interannual variability in the Hellerman and
Rosenstein (1983) wind stress creates deviations from climatology in the Somali Current
region, due to the formation of upwelling zones in the same place every year, and no
northward movement of the Southern Gyre. Figure 5.7 shows that along the Somali coast
in July, the temperatures get as low as 130C, yet the climatology shows isotherms only as
low as 22 0C. While multiyear averages would smooth some of the isotherms, there would
still remain a strong packing of the isotherms along the Somali coast in the model that
would-be significantly cooler than the 220 isotherm. There are some further improvements
to the model climatology available from increased resolution, such as correctioi of the
packing of isotherms into the "stairstep" shelf contours along the Somali coast.
B. COMPARISON WITH CURRENT DRIFTER STUDIES
The SCM produces a vast amount of archived data, and the vector plots generated
from this data reveal the synoptic picture of the currents in the Indian Ocean as the seasonal
cycle progresses. The realistic circulation of the SCM is strikingly apparent when
compared with studies of drifting surface buoys in the Indian Ocean. M, inari et al.
(1990) described the current distributions derived from surface buoy trajectories in the
tropical Indian Ocean, analyzing buoys deployed between 1975 and 1987. Qualitative
comparisons were made of the figures and descriptions of Molinari et al. (1990) with the
34
SCM output. Although a direct comparison of the data sets-to generatedifference plots
could prove informative, it was beyond the scope of this study, and must be considered for
future work. The SCM results-matched- the descriptions of the surface circulation patterns
by Molinari et al. quite closely, and monthly average current vectors deri- zd from the
buoys are shown as Figures 5.13 -5.16, for comparison with the 37.5 m vector plots of
Figures 4.1-4.6. During the boreal winter, the SCM does-not have the strong eastern
boundary current shown by buoy trajectories along Indonesia, between 50S and 10'S. In
the Bay of Bengal, the model shows a separation of the western boundary current during
boreal winter at approximately 17'N, approximating the separation at 19°N described-by the
buoy trajectories. The buoy average velocities in-March show-a meandering of the ECC-in
the western Indian Ocean at 5'S, a feature that is closely duplicated in the model vector plot
of Figure 4.4.
C. MASS TRANSPORTS
Monthly mean zonal mass transports for the major equatorial currents have been
calculated for Year 4 at four longitudes: 600,700,800, and 90'E. In taking on such a-task in
the Indian Ocean, there were several arbitrary definitions made. Undercurrents with closed
subsurface isotachs were segregated from the mass transport calculations of the surface
carrents as much as possible, and surface currents were calculated only as deep as 610m.
The EUC was considered to be the eastward flowing undercurrent during the months when
it could be distinguished from the ECC. In May, it had surfaced to be included with the
ECC. Although an eastward current occurs throughout the year at approximately 50S, it
was not calculated as an explicit current. The eastward-flowing ECC was defined to exist
at a given longitude from the time when it could be distinguished from the waning SMC
and Wyrtki jet in December or January, through the end of May, when it was included with
the SMC (as it could no longer be considered a countercurrent). The SEC was defined
35
throughout the year, and-was, with few exceptions,-the equatorial current with the greatest
mass- transport. Surprisingly, the NEC and -the westward flow which remained to the
south of India during the SW monsoon could be calculated as-a current throughout-the
year. The results of these-arbitrary definitions and calculations are-shown in Figures 5.47-
5.22.
The zonal mass transports are illustrated in Figures 5.17-5.20, while the variation of
mass transport with longitude is shown for the months of February (Figure 5.21) and July
(Figure 5.22). Several trends are evident from these figures. First, the EUC achievedzits
highest mass transport at 70'E,and weakest at 901E. It peaked in March, except at 90 0E,
where the maximum zonal mass transport occurred in February. The inclusion of the
surfaced EUC with ECC calculations in May, combined with the Wyrtki jet, resulted in a
peak in the ECC in May, except at 90'E, where it peaked in April. June was-the strongest
month for the SMC because the Wyrtki jet was included, thereafter showing a general
decline as a result of the waning of the Wyrtki jet, and increased northward mass transport
by the Somali Current. The SMC reached a secondary-peak in October/November, with
the second Wyrtki jet. Figures-5.22 and 5.23 illustrate the significant variation in the zonal
mass transports with longitude, showing greater variation in February than July.
D. OBSERVATIONS FROM ANIMATION STUDIES
In the late stages of this project, some data analysis and animation tools became
available, which brought new insight into the model output. Monthly mean tapes were
analyzed for the global ocean for four years of the seasonal cycle. The temperature fields
v, ere displayed as raster images, using various color schemes for enhancement of details.
The prominent feature of animation of the global images was the strong, regular seasonal
cycle in the model, which was much more significant than any interannual variability.
36
The animation of the Indian Ocean data set was even more revealing. A time series of
122 three-day instantaneous archive tapes were analyzed for the variables u, v, and T,
encompassing year 4 of the study in the Indian- Ocean. The richness of wave activity is-
striking, and shows the eddies at work in the model, transporting and diffusing heat. The
animation of three-day intervals is very smooth, with jitter only at the end of the year where
the loop goes back to-the beginning of Year 4. Figure 5.23 was generated prior to the
animation. It illustrates the standard deviation of sea surface slope for both the annual
(Figure 5.23 (a)) and monthly (Figure 5.23 (b)) wind forcing phases of the model. The
strong eddy activity implied-in Figure 5.23 (b) is quite prominent in the animation. The
eddies appear to be lee waves in the -zonal flow past the tip of India. Animation also shows
the northward movement of the cold temperature pattern associated with upwelling, as the
Great Whirl separates from the Somali coast. The deep effects of the Somali Current and
associated gyres can be-seen, where temperature patterns similar to the surface patterns are
visible at-multiple levels. The meandering of the ECC in the western basin in March shows
up strongly in the temperature fields.
Animation of the 160 m level in the ocean is quite striking, illustrating the westward
transport of heat by the SEC and NEC in January and February, while the equatorial
eastward transport of heat by the EUC becomes evident by March. This eastward transport
of heat at the 160 m level is strongly enhanced in May and June, as the Wyrtki Jet and the
EUC merge. The warm pool of water transported in the eastern end-of the basin circulates
cyclonically in the Bay of Bengal as a coastally-trapped Kelvin wave, and propagates
around the tip of India into the Arabian Sea. This pool of warm water serves as an
excellent tracer for the eddies formed at the southwest tip of India. Animation of the
temperature fields supports the theory that th,- westward equatorial undercurrent is due to
relaxation of water piled up by the Wyrtki jet. When the surge of warm water transported
37
eastward by the Wyrtki Jet reaches the coast, it appears to reflect back-to the west during
June and July. The animation dramatically illustrates the role of the-SEC in transporting
heat across the Indian Ocean-and into the Agulhas Current, as described in Semtner-and
Chervin (1988). Not only does the SEC transport warm water from the Pacific, -but
concurrently with the northward-travelling wave in the Bay of Bengal, a southward-
travelling Kelvin wave brings warm water into the Indonesian-Australian passage, where
warm eddies are shed into the-SEC for transport across to the Atlantic.
Various sections-of zonal velocity were animated to investigate the issue of upward
phase propagation discussed in Chapter IV.C. Animation of meridional sections showsan
upward phase propagation of-u velocity throughout the seasonal cycle. The-hypothesis that
this upward phase propagation is due to westward propagation of a feature with some
vertical tilt is supported by animation-of a zonal section of u velocity, taken along-the
equator. This animation shows very definite westward phase propagation to-betaking
place, and suggests that further investigation into this-phenomenon is-warranted.
E. CONCLUSIONS
While further improvements may be gained by improving the horizontal and vertical
resolution of the model, the continued improvement of global ocean models clearly calls for
better climatologies of wind stress, incorporating greater resolution and interannual
variability. Improved bathymetry in the model is desirable as the resdlution is improved,
accompanied by a more realistic representation of islands. The study of-Killworth et al.
(1990) indicates that the calculations involving islands may be tractable with a free-surface
effect. The use of such large models generates massive data sets, requiring new
visualization tools for analysis. The animation tools explored in the course of this study
were tremendously helpful in understanding the features of the-circulation. While other
improvements are also desirable, including the addition of the Arctic Ocean and improved
38
modeling of the mixed layer, any major changes-must be tested carefully before embarking
on a task as extensive as this. The parameterization of surface heat flux according to
climatology of temperature, while less desirable than explicitly -prescribing the heat flux,
remains the best option, as suitable climatologies of heat flux are unavailable, and heat
fluxes remain an object of extensive investigation and discussion.
The Semtner-Chervin eddy-resolving global ocean model accurately simulates many of
the features of the seasonal cycle of the tropical Indian Ocean. Model output shows that
this global model captures details of circulation previously available only through regional
simulations. The model simulates-the developmentvof the tropical circulation-in the two
monsoon regimes, including the South Equatorial Current, North Equatorial Current,
Equatorial Countercurrent, SW Monsoon Current, Equatorial Undercurrent, and seasonal-
Wyrtki jets The seasonally reversing Somali Current develops a Southern Gyre and the
Great Whirl, and seasonal undercurrents The model clearly indicates a seasonal,
poleward-flowing circulation off the western Australian coast, simulating the Leeuwin
Current. Mass transports of the zonal equatorial currents display considerable variability
across the basin, and the throughflow from the Pacific displays a strong seasonal cycle
with small interannual variability. The model monthly mean temperature fields show a
good agreement with climatology of sea surface temperature, and the current vector plots
are in agreement with surface drifting buoy studies. The analysis of the SCM output in the
tropical Indian Ocean suggests that the model is capable cf producing even better results
given better resolution, and improved wind stress, incorporating interannual variability.
39
APPENDIX
/R tPIC /.OP ,Z.. IHOIA
'"o ..- A+r _,0~ c -~ - -4-- -"
NOVMBE IA
-- MAc - - -
- " " A M-f l 7 , " TI.-.. -
0 AF- IR'PLQAr, CU"TA IX
.m , . .. .
SLOMGIruVE
.... .,Ki+$///j? . i.- '--V
-j- ~ '/; ur*~y / ' ?'
47"r"I . " ,
L 40
~~our~~~-~~r, A.~ CA ___ -. Ilc' t
0IC~ V - . Al U IIO' __
40- too--
(bj-
Figure~ ~~~ 1. Sufc iclto fteIdaiOen(ikr n3PEmney 92.()Nrhatmnooad(Suhetmnon
IOVTA- .40
EbcrOios a. 0ag o-niae rmi bevtos
0.k-
.'K le . 0
*0 20 :- 00 *00. .
. ......... **..................*......*.........................*..............**...
.... ... ..**..*.........~ . **............
............. ......................... .......... .4 ... *......
........... . . . . . . . *..*.*. (....................
............ . .. _.. ....
*......................... . . . . . . . . . .... * .
. . . . . . . . . . . .. ..... . .
.....................
....... . . . . . . . . . . .........................
Figre1...esiy.nd....iuton .f..........obsrvtins........................ ios fomLewtu (182
M .Sr.ceo.erv ..nsfrm.Hst......n..mb(179...
. . . . . . . . . . . . . . . . . . .
Bryan (1963)-
Bryan and Cox -(1968)
Bryan (1-969)
Semtner (1974) Cox (1975)
-Cox (1984)---------- (CME)
Semntner and -Chervin (1988) Klwrhe l(90
Figure 2.1 Aniecedents -of the Semitncr and Cherviii model.
42
T, S,U, V W TS-,u,v _w
610~~ mm2.847.5m 7i~m18.575
135 m4.5 m- 36 m 37.5 --
17 m- 25m-15 m
2475m 220 m ', 2. 62750 m
3025n 1000m
1330 m13m
1636 m-3850 mf
-2200m 22.5m
~ 4800 m5000 mm1
.. 52. 3 00 m
Figur 2.2 Vetia le60l imtmdl h etclvlct sdfnda hinerac betw-en 3 oxes TS ,advaeal eie ttesm
verica lee.m-prtr ndslnt r eieda h etro hboes whl . an v ar de.e at th.idonto.teve.ca.dgso
Figre2.2Vtha boxes. The t boe reTe etca vilocis (18)iaus oefne at 0da
time scale, while boxes below 710m are restored on a 3-year time, scale.
43
Figure 2.3 The global ocean model domiaini at 12.5 in. The only islands areAustralia/New Guinca, New Zealand, Antarctica. Other islands-havebeen shoaled or attached to continental land masses, and marginal seashave bcen Filled in-
44
LEVEL. 12.50l4 LEVEL 30n.0014
LEVEL zs7-fCM LUTL 42 1~
1t I "E w4t 4X.1 c
LE-vft I I
4!t~ 1" 2E 11t P
..
21S!I2K~Z12~
Figure 2.4 The Indian Ocean bathynietry of the global ocean model.(a) 12.5 mn, (b) 117.5 in, (c) 1 i60in, (d) 1975 m., (e) 3025 mn,
()4125 in, _(an) 5000 mn. and (hi) comp osite.
45
N . . . . . . .
r rJ
, ,, , ° - , ,,C'
, I, P I I \ -- ,. ,,
' '\ \ " - ' l |i \
ul-i
FT ' ,"'/
, \,' /_...,/,, .. .. ,/ 1I -' 1 1 1 ' ,'//11 i
ul I
V) In In
" " " ""/ i / u ------
"'S" ' i l/ ... ,,'.," ' '" 'ill
",____'__ , ", "" "S~i I~
" ""' 11,1 5 ,
" " " S 5 "' " . . . . 1 l","''- " ' "' I s " ,, 1
" ' ' ", . . .. ./ j z1/ / 1 /-~ *
*~ .S ... ' i i - * * .1 ",11. . . . ' / SsJ ,US,
0-
. . . . .. . . . I /L.. . . . . . .c
""5 """5- --" . . ' 5.. . . . . . 551
0..0 s0
Figure 3.1. Monthly mean Hellerman and Rosenstein (1983) windstress during Year 4. (a) January and (b) February.
46
z) n z V)
r rl
jL~9 t.1Ll
. . . ... . . .
IN Ch
. . . . . . . . .
tg. . .. .
.'.//.v .....
0..47L
7 . Is .. - '' '
stes duig er4.-a/Mrhan1bArl
4711
o 0 0 0 1 0O
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LI* * ' '' l
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- It
0I ----- -
0- ' /1,1 ~ I * II0* l / u I l
stes duin Yea 4. (a May anbue
I '~ " ' - 48
7. V) z zA0 0
('i wClNt
.~ . S ~ / / /- ~\ \ %* .- / / ..
- -~* 'S --'/ / /1 \ 5 AD
to ' / I' .. ~ I
-0o to,/
Lit k/. w _
Fiur 3.4 Motl ia ///rnan oesen 18)wnstesdrn er4 a)Jl n b u0t
49Ii~
0 0 0 0 0 0wi~ 0 0- rNli i
S. . . ... .. . _ .. . ..
.. . . ..
Li ) tllll i
i ii
ll a
,,///,,\\,0 ,-,-//--1-I///IU'il" ''/,//////
0a
., . . .- . .
j I , " i I I " " s / l t
I 'I'iii ". 'ill ! '- i l l.... ' il/ll
'I I p" il///ll/ ' -. '1//i.0 i /////, . .. /tltl...-...................
L-iIiI . ." l l i i' l l L i
CL.
\'' \\0.. -l . ... .. .._"-l
." ' S "" il ll .. . . . ..0l
N0
I,, I" 'll
00Li - Li Li
Figure 3.5 Monthly lnican ]Iellernman and Rosenstein (1983) windstress during Year 4. (a) Septemrber a'nd] (b) October.
50
o0 00 i I t 0
'CI
,I,~ \ -
wLi L
to to
o k. . . ! . . . . to.
. . . . . ./,.
to1
0" p, , 'L\\ " "?
CS 0)
S S - " ,l .. l /"
t4 IA
S.j .. ' 1 Ir ' ...... '/11/1"-"I/ /1. .. . .. . .. . ........ I/1/I/ . 2 m*- . . . . .. ,./1 1/ L
.. . ...............................................' ,
5151
" " .. . . . . . .. ' / I ! I I " " " " . .15 .. -
a .. -
o- " , " . " . . . . x , , - . . . . . " ta
Figure 3.6 lMonthly mean Illlermnan and Rosenistein (1983) wind~stress during Year 4. (a) November and (b) Decemnber.
51
0E5CE so,70E
...................
50 cm s'
C 0~
v ~ ....
10S
C 0C6E7OE 8 o
,2C,
January 16
-. 50c C11K
C,, 6III0; s --
/ '-' ' .
Figure 4.1 Instantaneous current vectors at 37.5 i.. (a) January 15, Year4, and (b) January 16, Year 5, illustrating interaiinual variability of theeddy fields in the model.
52
'VR Y, - 'ii.A
4hJy ~~tO
* :r-9-
j ',k
~ I - -
Figure~~II: 4. otl na urn etosa 7i uigJnayo
Yea 4.k
53.
Id" It I I., j j
I,-i
5;
Figure~ ~ ~~~~( 4. otl ia urn etr t3 ndrn erayo
Year ~ 4.~
54. l
1\ .*' ...
':7 ... 4... ... .
4~4f" I 'iIi
.... .... . .... Zi .. .. ..4 44r4
4
(4 '~:4'o
.--4.- ... .s 4
(4A
Ij
*~~44VI
j~~4~
44 4 4 4 14 n
.1 j 4'4444VI
Figure~~~~~~~~~~4 4.4~"4 Mon4l mencretvcosa 7 drn ac fYa
4.~
55/'I
z i/iC C) (C ci
hi A4. ~' 4 I, ~
**.. ~ i 1V~
hihi
.'.~.c-. *
~
k~~>~ ~
C,' hici . I.,.
IW~4 *.. 0
r ~Cd t / J~....
1,
t '/iiL.:.
IIUII I Ci
I .,....., I.
1j1li(~f~:.~l1~ 7
o __________
hi _____________ A'-
----.5..
i *. 5 .. )gI
I Ii Ill ~
. :Z.1 j-C 'II I f ~ hi
~ liii
h ~IJ.h-" ~I Cd ~
C~;-~:~. ~
2 ii~ *, -~. ~
/ ~C jii.( ~..A9~f-'
C- '.1c~.V.
* I-s-I-
C, - t~)
Figure 4.5 Monthly mean current vectors at 37 in during April of Year4.
56
V1
.... ......
I,,j
.. . ... .
-57
z *2
0 0
NOI 91
a. .. . .
Ct
nit.
A ,, * 'II,
r / 0
. ......
1.0~ .. =..
1..210 *-.
f.I 1~f~
4 .''4
58
II -.
U' .f J ........
~~ .. V ~ ,4l f:~ . . ..
RO MEIi I
4 ~ ''tiq_ON OEM
WARM.
M fASHMS
RAN o
-Un
...... f -I-"A p.ao
4 -. imp
0 411 ii
Figure 4.8 Monthly miean current vectors at 37 in during July of Year4.
59
'agai ............_
It ... ' ....
.. ... ...... *t
bf...."il
fto
i-I,
1" <-~
010
.C . ... ..
R, .... . ..
. .. ... ..I
kiUIi1
4X)
61.1
,
,,j~l
C3I
.. .... .. . .. ......
* I
V4,::~; Up
;;.~:Ali
(4 ia4
0.. . .. . . .
:z :::.. U..
Figue 411 ontly man curentvectrs t 3 indurig Otobr o
Year 4.
62S
'j,,
V I
lilt
IN)
.. .... .~
IR
Figure .12 Monhly mencretvcosa 3 idrn oebro
Yea 4.~~IIII
63.
-~ I/1 1.
UPC C
1Y:; Nj I
1,7;
o Ito
- Z .4 iaIi
W .i !i:'
..... ......
. .-Q
~: rf~l:I Ivy
0- *~j~j*~ ~ ' 1A
toi
T. ~s
ICC ~ ~ f ~ V1
-x to-
Fiue41 otl iancretvcosa 7 ndrn eebro
Year 4
64
LATITUDE 0.00EAST/1WES-T WIND STRESS LEVEL 0.0DM
30E 40oE 50E 60E 70E BOE 90E I OOEJAN ....... L.. JANTIED -E-
1AAR t ARn
APR- - APR
MIAY -MIAY
0 JUll - 2i /JUN
< JUL - H2JUL
hi AUG - - AUG
SEP - -SEP
30 OOE 50 60E 70E soE- 9OE I DOEA- 1/7DEG ROE3JUST DI/'3.rRrE THER1,,EAS CYCLE
COfNIOUn INTERVAL 0 1 (110 FIELD 111) -0 (3052 145 CO.I14cI1SCALE( FACIOR 1C2.0 FIELD MlAX z0 573 1132 COE 104C91
LATITUDE 0.00U VELOCITY VERTICAL INTEGRAL (12.5011-37.50M)
30:- 'OE 50-- 60E 70E DOE POE I OE-JAN - IJAN
T-ED -j~ ..... FED.I.A................... . ............
ANI - ?1- -...--- a-' APR
MAY F3 *- A
<1 JuNt) ~ { "- ~ JUNl
< JUL JULt- AUGAUG
sri'- ISEP
Nov - ~ 2~\~ NOV
DEC~,*... ......- ~*-~- - DEC
JAN :-'-JA207- 40E SOC GOE 70E E80E 9OE 100E
A- 1/2OEG P01DUST OIAGFREE TI-ERUI,SEAS CYCLECONTO'J7 INTERVAL m 20.0 FIELD IM= -01 5 145.5CE.204131
SCALE rAcZofl = O 1 FELD MIAX - 40. 1I" 50E,104562
Figure 4.14 Dependence of the Wyrtki jet on seasonal wvind stress inYear 4. Longitude-timie plots of a) Zonal wind stress and (b) 12.5-37.5m zonal currents.
65
SHIP DRIFTS + IQ
45*E 50* W5 60* 65' 70* 75' 80' 85, 90, 95*
Dj zo0
01 0
Sj 20A -4 A
66 2
LATITUDE 0.00U VELOCITY VERTICAL INTEGRAL (117.501M-i6o.oom)
30-- 40E 50E 60E 70E 80E 90E 10OQEJAN - I. I tI I JAN
FEB -V 42-- FEB
MAR - -MARAPR2V 62 toAP
A R -42 ------------- 20- AP
MAY -2- MAY
2 JUN ---- *-- JUN
< JUL 4 -JUL
LI AUG-~ ,*.- AUG
SEP SEPOCT 4
OCT
Nov 2 2 I.- DEC
-gI \- - -1 JAN
50 'OE SE 60E 70 GOE 90E IOOEA- l/2DEG ROBUST DIAGFREE TIERM,,SEAS CYCLE
COfNTOU'l1 E1lERAL = 20,0 FIELD MNII= -40.3 161 .50E.10407)SCALE FI.CT0Ul r I 0 FIELD IHAX = 62 3 too oor.104(33)
Figure 4.16 Longitude-tine plot of the EUC during Year 4. Zonal currentsintegrated between 117.5 and 160 In.
67
U VEL0C Y LATITUDE 0.00
30E -OE 50E 60E 70E 60E 90E I OOE
37.5 -1..37.562. ,. 62.562.5 ............* 87.5
117.5 1 j7.5
160.0- 160.0
a 222.522.tu
LiL
310.0 6. 10.0
30. 0 0 0E a0E 90E IO~
... I * I . ...... .... 1.0
SCi FATO 17.5 FIL A 49 195117.5N
U~2 VEOCT LAIT 0.0
30C "-Or 50E 60E 70E BOE 90E I0WE
CONTOUR LNEAA 6 .3 FEDMN= 7, 6 Z2.5-M
17.5 Jaur and~ (b)~ Leb1175y
I 68
U VELOCITY LATITUDE 0.003 OE L0OE SOE W0E O0E 80E 90E 1 OOE
2 .5 * ........ 27.53275 - . 62.J3 587.5 J 8.* 7.5
117.5 -j 1 . A17.5
160.0 -1 2 3160.0
a 29 35 222.
4I~35.0
6110,01 610.030E 4.6E 58E6000iE E 90E I OOc.
A- 1/2OEG ROBUST 0IAG.FREE TMERM.SEAS CYrCLECONTOUR INT1ERV~AL = 7.' FIELO MIN =--56 3 151 zo.12.5MI
SCALE FACTCR v 1I= FIELO MAX . 62 3 177 S0E iI7 SM)
U VELOCITY LATITUDE 0.004C '.0r 50r, 60E 70r- SOE 90E ;OOE
17 5 5M -5
~2 5376.5
17.5 11.
6C3-A~' 160.0
Z; 32 7 .O
/*
6.0f610.040! 5C 5E 60E 7C 1C 00E
A- /2DES R05u57 DIAG,FREE TVh=RV.SE:AS CYCLEC'UNTCA [?!ERVAL. 5.= FIELD MIN~ -25 9 157 SCE.612.cm)
SCALS PAC70q = I.e., FIELD MAX * 6. 7 1 07 CZE.12.9-Pl
Figure 4.18 Monthly mean zonal currents at the equator during Year 4.(a) Marchi and (b) April.
69
U VELOCITY LATITUDE 0.00
30E '-O"E 50E 60E 70 E OE 90 I OE
1215 1,12.5
37.5 IT 37.562.5 -6 .
117.5 *----- 117.560.0 1.60-.0
cx 222.51 222.5
-..... 2..2.
310.0 , 10.0.... ..... 2,7,
;IS'15.0 - L -35.o
3 0£ E 0E 50E 6O0E 70E 8 0E 90E I 00Ec
A- 1/2DEG ROBUST DIAG,FREE THERI.,SF'AS CYCLE
CONTOUR INTERVAL = 9.0, FIELD MIN = -35.4 f77=Z.310.0M)SCALE FACTOR = l.eoJ FIELD MAX = 110. i67,00E.12.SM)
U VELOCITY LATITUDE 0.00
0E 4-Or 50E 60 70E 80E 90E IOOE
t2 1 2.I
37--. 3 7.5
87.5 - , .-,-,7..5. I 7.5i ..... ...0 ..~0.~F - 160.0
222.5 . 222.
. 61
I0. -1 :, . . .- . .. .7 . = 90, M E
'-25.3 -. # L4i5
61..0 -2!.;" ..- ./,-610.0-
30E 4'08 508 608 7C8 808 908 1 008
A- '/2DEG ROBUST DIAG.FREE THERM,4,SEAS CYCLE
CONTOUR INTERVAL = 120 FIELD tIN = --e 6 qOeZE.27.SMI
SCALE FACTIC . 1.03 FIELD MAX a ;ST. 1,(, = E,i2,5 1
Figure 4.19 Monthly mean zonal currents at the equator during Year 4.(a) May and (b) June.
70
U VELOCITY LATITUDE 0.00
30c. .Or 50E 60E 70E B0E 90E I OOE
37.5 -J 3." . - . 7.562.54 -.. :.\.y875 - . 117.58..7.51 - I .7.5 2 7
S , ....... . ... .1600- '. . . . ,.o,,, 16.0222Q 222.
io0.0 3 10.04315.0 'i2.
610.0 -6M0,S I I !.J I II I
30E 4-OE 50E 60E 70E 80E 90E 10CC
A- 1/2DEG ROBUST DIAG,FREE THER.M,SEAS CYCLE
CONTOUn INTERVAL = 1.0 FIELD IMz 9 1SZE.1,7 SM)SCALE FACTOR 1,3 FIELD MAX = I;4. 144 5ZE.37.Sfl
U VELOCtTY LATITUDE 0.00
30E 't0E S0E 60E 70 BCE 90E 100£
7.5 I 17..
6001 I 60
I ' 22.5
310.0
640.0 6. 05.03CC '-C ' I I
E 4-0E 50 60 7C B0E 9E 00
A- I/2DEG ROBUST DIAGFREE THERM.,SEAS CYCLECONT-C2' INTERVAL z :.o FIELD MIN = -63 1 Iq.SCE.e7.S4I
SCALE FACTcR 1.,3 FIELC MAX - 139. I,4 SCE.37.SMI
Figure 4.20 Monthly nican zonal currents at the equator during Year 4.(a) July and (b) August.
71
U VELOCITY LATITUDE 0.00
30E E -OE 50E 60E 70E SCE 90E OOE
12.5 .......- I. l ' 12.537.5 37.5-62.5 - 62.58 7 ,5 J * 87.517.5 ~J0 " , h 160.0
:221 2 2;:310.0 %X'', 9 310.0
41-5.0 J 7 435.0
30E 4-OE 50E 60E 70E 80E 90E 100E
A- 1/2DEG ROBUST DIAGFREE THERM,SEAS CYCLE
CONTOUR INTERVAL = Q.03 FIELD MIN = -30 7 I61 . .E.12.-Im.
SCALE FACTOR = Ii0o FIELD MAX = 112. 144 50E.37.S.1
W VELOCITY LATITUDE 0.00.OE /-OE 50E 60E 70E BCE 90E IOE
I I I I I I , I I
62.5 4 / ( 37.562.5 211 .
87.5 8 L 67.5117.5 -117.--6o0o,0{ 160.0
C- .12 222.5222.51 322.
124: 0.0 G 310.0
4 n23 5 .0 5 ,i iI I :':
.2 2
610.0 Ii ,"610,0
30E :-OE 50E 60-r 70E B0E 90E I OOEA- I/2DEG ROBUST DIAG,FREE THEPM.,SEAS CYCLE
CO:CITCt INTEQVAL w 6.20 FIELD HJM --4+3 154 CZ-.i2.5m)
SCALE FACTOR - 1.03 FIEL0 MAX - 84 3 144 50-.37.5m)
Figure 4.21 Monthly mean zonal currents at the equator during Year 4.(a) September and (b) October.
72
UI VEO1-0c IT Y LATITUD~E 0.00
~ ~ 50:- 60CE 70= ec CE IZ
2.52.5
( A/1 1 1~ I 62,5
1-27.5- ;1 37.5
S222.5- L : :Z .* $:22.5
2- V11
I 29
3CE 4LOE 50E WE ;,rSQ 9rr IOcE
A- 1/20EG .108LST OIAG,rREE- vfERm.5E-AS CYCLE
SCALE FACTCR I I.0 FIELD V'AX v 77 6 15SCEI.~
Vj VELOCITY LAT:TUDE OC-
cr 4C 5o0E E 7C c 9co 2C^
2.5 ZM C,, I- ,
thlkw1~ -*z
1...
61.
A- 1/2DE-- R05427- DIAG.FRZEr - VEA 'L
SCALE ;AcZ : f ,;!n ;:*.o -AX m 1 st f; ~ i2
Figre .22 Monthly mean zonal currents at the equator during Year 4.jFigur 4.22 (a) November and (b) December.
73
U VELOCITY LONGITUDE 8O.00OE
20S lOIS 0 ION 20N
62.5 6~,... .2.5
87,5 A 87.511 7.5 - :Ik17.5j -
160.0 1. 0.E
a222.5J 222.5
610.01 [610.0
0S I 0 1ION 20WO::A-~ SEASONAL FORCED MONTHLY MEAN
CONTOUR 1?17ERVAL = 500 FIELD MIIN = -5/ 3 IQ 50N.12.51i)SCALE FACTORl m :00 FIELD AX x s5 9 14 5SS12.5tli
U VELOCITY LONGITUDE 80.OQE
20S 10S 0 ION 20N
t- 87.5
8722. -- 22.5
S310.0 1.
&.35.O - -ll ~35.0
610.0 610.0
20S ICOS 0 ION 20N
A- SEASONAL FORCED MONTHLY MEAN
cowroui INTERVAL = 5.20 FIELD MIN m-E5 3 I0SN1.I
SCALE FACTOR = 1.00 FIELD MIAX = 59 3 (4 OOS.12.StfI
Figure 4.23 Monthly mecan zonal currents at 801E during Year 4.
(a) Janluary and (b) February.j
74
U VELOCITY LONGITUDE S0OME
20S lOS 0 1ION 20N
117.517.
160. 32oa l,10.0
1 5
610.0. 610.020S OCS 0 ION 20N
A- SEASONAL FORCED MONTHLY MEANCONTOUR INTERVAL = 5.00 FIELD MI N =-29 7 117 SOS.12,SHI
SCALE FACTOR z .0 FIELD MAX = 62 9 10 SON,160 .DXI
J VELOCITY LONGITUDEz 80.OOE
20S 105 0 ION~ 2 ON
2.5 w~i12.527.5 v1~~/: . fuI:~.d 37.5
62i 5 62.5
222.5 87~ 2.5
31oxO~ VO 3210.0
610.0 V______1610.020S lOS c ION 20N
A- SEASONAL FORCED MONTHLY MEAN
CONTOUR INTERVAL = 5.60 FIELD MN T -34 6 (14 SOS.12.Sm)
SCALE FACTOR = 1.00 FIELD MAX - 55 9 11 OON.12.SM1
Figure 4.24 Monthly mean zonal currents at 80 0E during Year 4.(a) March and (b) April.
75
L) VELOCITY LO1NGITIUDE 80.OOE
20S 105 0 10,11 20N'
12.5 In2.5\
87.5 -l i .7~[8.
222.5 22.
310.0 L610.0
20S lOS 0 ION 20N
,A- SEASONAL FORCED MONTHLY MEAN
CONTOUR INTERVAL = .00 FIELD MIN =-33 9 12.50S.12.514)SCALE FACTOR m I.A0 FIELD MIAX = 10. 10 00, 12. Sti
LU VELOCITY LON-.T1UOE 80.OOE
20S lOS 0 ION 20N
12.5........ 12.5
62 5w "K 62.5
1177.5
P1 "~~I~i\222.522 5-
210.0
4:5.0
610.0 -T -4610.0
20S lOS 0 ION 20N
A- SEASOIAL FORCED MONTHLY MEAN
CONTOUR INTERVAL = S.03 FIELD MuIN = -34 3 Il-lC3S.I60.0MI
SCALE FACTOR a .DDo FIELD MlAX - 1I0. 10 03j2.SIl
Figure 4.25 Monthly mean zonal currents at 80*E during Year 4. (a) Mayand (b) June.
76
U VELOCITY LONGITUDE 8O.OOE
20S lOS 0 ION 20N
62511.5
- ~822.5 -' r22.5
10.4
0Id . 310.0
435.0 -4.35.0)
610.0 .610.0
20S lOS 0 ON 20N
A- SEASONAL FORCED MONTHLY MEANCONTOUR INTERVAL = .8 '0 PILO MIIN = -56 a 11 SON.87.51,1
SCALE FACTOR - 1,00 FIELD MlAX z 86 '2 15 00N.2.S5iI
U VELOCITY LONGITUDE SOMOE
20S 'cs 0 I ON 20N12.5 -2.5~
62.5 8.87.87.
87.5 I~ 7 625160.0 . Z.f I;,
160.C
a 222.5Il 2.
4-.35.0
610.0 Pil ___.__ . 610.020S 05s 0 ION 20N
A- SEASONAL FORCED MONTHLY MEAN
CONTOUR INTERVAL = 5.88 FIELD MIN - II 00S.12.SNISCALE FACTOR . 1.88 FIELD MIAX 889 7 I5SO5N.12.5mi
Figure 4.26 Monthly mean zonal currents at 800E during'Year 4. (a) Julyand (b) August.
77
U VELOCITY LONGITUDE 8O.OOE
20S 105 0 1 or" 20N
#2.5 12.5...
37.5
87.58.50
117 S -0 0 7.520
A6.0- 4ESOA 1ORC0 OTLYMA
4.0S e-OS C OC
625
6 310.0 6~ 10.0
ijpI. VEOCT K\ GI D 800.020 OS 0 1 ON 20%
CO12.5TRA S2 ILDII ~ D~ 12.511SC7L5 37TR= 15 ILDIX ~ 18 I 5.151
Figure .27 Monhly men zoiia curretsa80E urn Yer4(2.5 6e2.brad5b ctbr
87.5 - 878
U VELOCITY LONGITUDE 80.OOE
20S iOs 0 1.20N
62.5 -62.5I160.0 11 7.5
.160.0 10.0
0222.5 2225
610.0 61f.--1---0.020S lOS 0 I ON 20N
A- SEASONAL FORCED MONTHLY M'EAN
CONTOUR INTERVAL = 5.0 P IELO MN = -06 1 19 5CZ4 12.541SCALE FACTCQ - 1.00 FIELD MAX x 77 2 10 SON 2. SMI
U VELOCITY LONGITUDE 8O.OOE
20S lOS 0 I ON 2C0N
12.5
117.5 L 11 '.5
1600 4 0.0
0 222. I 227.
4-35. ' -.35.0
A- SEASONAL FORCED MONTHLY MEAN
CCUTCUR1 EZJTERVAL - S.2.3 FIELDOI 0 0SNI.M
SCALE CACTOR - 1 0 FIELB MAX - 4*1 Z1.m
Figure 4.28 Monthly mecan zonal currents at 80'E during Year 4.(a) November and (b) December.
79
.3 vE,-CC -y ~T 0 02
2CE 4c E 50E 5 E 'CE SCE 9-'E ICOE
1-7.
a;22.S I~ 2
- 1 0 , 00
C.~ C.V-
6110.10.0
20C 4 t s SOC0 705 8CE 005 20oc:
A /DGROBUST OLAG.rPEE TIERM.SCAS YLCON05M14 18lEA 2Z.3 NELO 11111 - -7"7 6 16300 7 5ml
SCAt ACTC71 . 1.02 FIELO 865 - 57 0 176 OCC.11 S.)
J VEOcr L3-N!;J2O 60.00E v3 "ELIC! LT:-*;- OE 70.-.:;2:S i0s 0- I0% 2014 205 S 2 I? 20v
15 ...... 12.5 12.5 , 2552 ," 27,57s 27S- 5M. 52.5 U 5.- 87.5 81.51 .#.
160.2 - 62 l5:.OJ 150.0
uL 31.= j[12
(b) [.1(c)
610.2--502 60 1.22 21 01. 20N 2is v00 0 % 0
A- I/220G R05135T CIAG~f855 ThC7.SA.SEAS C-C-f A- I/2GEt7 ROBUST MGA.Mr EC -sM SEAS CYCLE
5001.0 C*025 1A 5 0
2'. Q. 5 its 25 12.511 SCLE ;AC*C6 q 1 lz- XEL^ PAX si5.t I2SlN,117.1
875- 37 5'~' *
S' 7.5 - v~[1.
'1 5^..0
312C OXL51
- ~~1 0 )1. 7. 10-5
A1/20EG FC!Yj5T U'A3,F;8EZ .R. SEAS CYO..t A-'25 VM S 0'AZ.rRC!TEvSA YL
5255 025 * 51 CL .5 . 54 2 44ItS1,s V.5,1F00~6* 85 F1
5L-. 16 4 4 11..2VI62Il
Figure 4.29 Mean monthly zonal currents in February of Year 4.(a) Meridional section at 01, (b) 601E, (c) 700E. (d) 800E. (e) 900E.
80
t; vrc -tAT.TvJE COO0
40 ~ E 50E 6 . 7 Se CE 90-- 00
60 0- 2..........I'
27 2.
r
4250~ - 4-
:!CE LOE 5CC 60E 705 B;E 90E: I 005
A- I/2,IZG RCSVjST OIAG.AREE ThER.M.5EAS CYCLE
CC41rCj INZEQ'AL - 22,0 rIELD t-I -40 S Isq S7Ir I', S.SCALE CAE-,-^ - 1 1. CELD A * Z 144 S111-3 511
U CC~ ~ C7J0s~0 6~.CE ~ ' ~~.Q'~t
160.7- ~ 1167
(b) (cA
:2' " .0, t" Z1.7 Isz:.f -AC*".. I 2. sev . Mc CI. 117:1 .2s 5 11 523 I ?..
'Os 205 Ic5 C.. -ON
-. ;".5 1~- , " v 27V 5 . 1
-7: -1.
r6. (eIO.
US 1 . C 1' 0 0V. Z01/ -JS7 CCj ' AGS)655 Tltt SEAS C-L A- 1/20EI; RONS57 CIAG-JACC Th"E4V SEAS CYC.
C-.--1' * I : .. . 96 l 57, 1, 1-1 "IM ZW2V - .. .1 1-~ *I - .)G-; it. Si-121a 5? 2Sisc0L( V1iTrs . 1 2.1 ~ NI" PA 64 1 I IIS 1% 2.S-1
Figure 4.30 Mecan monthly zonal currents in July of Year 4. (a) Meridlionalsection ait 0*, (b) 60'E, (c) 70TE, (d) 80'E, (e) 901E.
81
777
0 ~ - .. .... I
J, I
C-5
Figure~~~~~ ~ ~ ~ ~ 4.1 Vcojlto h qutra necreta 1175mo
Marc 10 fiYer 4
30 S 30N
2 22.-5
,0.0 :. .. .. ........,310.0
00
~1975-0
-i- \ -,"(".... .. - 3,
-) \\\*\ NN
1 "
7c~- -©
t In O//
V I
a, \
F'igure 4.32 Deep current structure in the equatorial Indian Ocean. This
plot of zonal velocity (cm s- l )at 85E on 19 March of Year 4 illustratesthe complex deep current smnicture in the equatorial region.
83
0 0
Ail'
R.-
o ,,, -,,.+ . ....- + .+. ,. .. .. .//
11/Ij to I
+ /
z ii,
VI"
+,.+ ,'.++ + , - I I0
-+ : ., + --,.J....:.+. - r :
,+ N- I '
Figure 4.33 Mean monthly current at 4125 m during of Year 4. Theanomalous currents in die Celebes Sea are due to bad data discovered inthe Hellemian and Rosenstein data set durin.g the model run.
84
" ' - m I-I P
CASEA ",PARALLL OCrA% CLIMATE MODECL (PCCM) 1/2 DEG WGfLC OCEAN N0. 2
LATITUDCE 0.03U VEL , - LEVEL 425.00M
40E 50E 60E 70E eOE 90E i 00E
JAI .I I I I
FEB ; FEDIN
I W zE ........................ ............ "..... ... ...... YI \I! ~APR --jM.AY JA
JIMv
E- .O.. .-.. ,.. L .o C
, ... v - :'!A " , ; ,'s""': ... ";;.'-., ..- o..SEP 4
- SEP
DEC nov
JA~l JAn
40 50- 60E 70E 60 98E t0-
A- I/2OEG ROBUST O!ACFREE RHERM..SEA5 C'CL-
CO.'grco- 1'5TEUvA- 5.20- FIELO r-IN z -37 1 153C2EE-;2405)SCALE rAtft7P z 0 FIELD 'lAX x 31 5 169 czL.140
Figure 4.34 Longitude-time plot of Year 4 zonal velocity at the equatorat 435 m. A system of westward-moving regions of convergence anddivergence is visible.
85
0 t) I'
J/-J ...........
.. ......
- .....jU..........:
I -.- : -,,4 I , l, 3
.. ......J(:;:~rI ...... __
.0g~
-15
t "I -s
0j a
,Figure 4.35 Currents at 435 mn during March of Year 4.
86
(*l
.. i7\.I C'.
ki\~5.11
7
hi_ _ __ ;
II.III ..C-ML
j3 Cl ~ tf%'~-L
Figue 436 ear4 W st ustalin crret vcto an tepratrepoat3. ninJnay
- - 87
V-)
0 -ibjA
.... ....
VC,,
I- Ot ... .. .
0 0
IIi M.9 h~ -
FigureP.-. 4.37J Yer4W sIutaincret etrad-e prtr lt
at375 n n ebuavp
88_
000
tki~
(1) A
II
If-
.. ...... .....
w w
a 0 .~!.....
tr, C1 . 1'(A In -A (A?~-~- H
* -20IN M
Figure~~~~~~~ 4.38 ~ Yea 4 WetAstaincurn eco n tmeaurlt
at 37. in in March.
89.................*
0
-AJ f
0
a.''Eno ~ 1 _ _ _ _
U 00 0
at 37. 5_m_-in___ -
90.
IA V) 0/ CA'0 0 0 0
g .. __.__.._________ ___. 0
0
td
S0 00 M
j W00
• . , II It - '
LII
.....~~~ ~~ 1.,'Z- -, I :: ........ ,-.II i . .. • I3- ..
I. * . ... ., * . 3333.l
... ........,, -'.-3 ,.,-, .11IL ,,
,........... . ...
10 tJ Z , ... . • ... .-. . :: ",, : .. ", ,: .... t
at ~ ~ ~ i 375i -nMy
o \. , . . .. ....U U_
Figure 4.40 Year 4 West Australian current vector and temperature plots-at 37.5 in-in May.____ _________
91
LLJ ILII
I _ *
hi"AV
C-
hi -~ In InInI- 000
Fiur 4.41 Yer4 e'Asrla urn vco n eprtr pos
at 37. ininJune0
~ " ~ 92
in W/ In I0 0 00
to- I)M0 -. ~
(II
Ijd
o 0,
61.
Ix
I 'n. ... '.
Ir
Figure 4.42 Year 4 West Australian zurrent vector and temperature -plotsat 37.5 in -in July.
93
L4 (A 1/)
0 0IjJ
0 -.
C4
tI-
IdwI~I 'k ___to
*'kto
U 0 .0.... 0.
Figure 4.4-- Year 4 West Australian current vector and temperature plots-at 37.5 m in August.
94
En
o ) 0 0
o I * Io
.V r
to (n'- 0 ,,
a0 0 0
N VIfl + ____ I ___________ ___
0 0
_ ... *.,..
"i I .=IIl ,
..........:+ ;i. :.. .... .. . . .
oW
Figure 4.44 Year 4 West Australian current vector aiid temperature -plotsat 37.5 in ii September.
95
In UlL' I
< 4)..rr
10L- ~-
CL7:-
V) L~nv* -"I,
i ~
tO "I "'.
a 0I m
at 37. ini O tbe .
96
C--7
En I
~~i kJ~/
0.1
..: : .........
1 1 - , '-
. . . .Ir 0 !
--- I - -1 , .- 1
I II'~~~En-II \'*~~0
Figure~ ~ I 4-46Yar4-WstAutalancrrnvctrantmertuepltat 37ki. £i in November.
97a
C IL to0' ~ I____4r
ILIL
! .. .. ",-
-i . . .... J 2... , ....
FA 0
0 a~
Fiur 4.4 Yea 4- Wes Aut
raia curet-co and temeraur plot
A_ at 37. in in Dee br
S I. t I 9
I- 0 Ci 0
;'iure4.7 Yar4 W sl usralancuren ve-radtmprtr iat 375 ni Dcmbr
V9
~. ~ (b)
JIM
(c) r. ., (d)
0_ .23 4 16 17 -21
1.1M C
Figure 4.48 Comparison of model output in the Lecuivin Current regionwidli LUCIE data, as reported by Church e! aL, 1989.(a) September 1986--February 1987 mean alongshore currents atDongora, (b) Model mean velocity in January. Year 4, (q) Potentialtemnperature at Dongatra-during 7-9 June 1987, and (d) Model meantemprature. during- June of Year 4.
99
?0
0 o)
200
0-0
-J*00/'Y I? m titvI
o 0
o 0
N N
00
c~~ N - - CN C? l N -N C
Figure 4.49 Indian Ocean surface beat fluxes (W rn 2) from:Rao
et al. (1989). (a) January, (b) April-, (q) July, -and -(d) October.
100
I i'
Fiur 4.0 Ida ca ufc et-lxs( j2 rmH sert
-an La b-(199).(a Ja way,(b)Ap i(Jul,-ad(d ctbr
C 0 L
C) Ci V
A,, d oii
Ci 1-2. (aCaluay ( ) Ap il (c) __y--n (d co e .
102
yb(S 0 ( 0
(S Iell,
AS, i'
by CS *
VA in
/' i:2r b"J~i hi h
too
O i10 0 'c I .
0 LO W
('44 Q' 0Nr
hiy and (d O'ctober).
103
..... .. .. .,
(a) June 2 1,'..-', (d)Juily 141 /f,¢ q;k;:lN - /.-tT . . . - € - "' :; _v: ; h '1
I t,
- 04
-, f
,o o O SC... ..... .. .................. -................................. • • ........................I. 1.. .........
kb) hne 14(e) August I
,.77 ,,0., 1' 100 c S,a. J ,, -. -- ..\ NWT.i ' .. . 4 °t . ... . . .. " '
-- -'
. .. -- -----------.. .
100 $00" - - , * 100¢
.......... -. .. -
(a) J _ 14-, - . 1,
( f A u g u s t t1, ,-: -
104
........ ........_d....... ............... ... it .:. ....... ... .-.-
- - - - -- - - - - - - -- .' , .. . . .. . --. . . . . . .
,-.>. .. .. .. ....- - - - -:,.. . . . . . . . . .. . . .... ... bT .'- " ,' > . .
, " i(0 August'. 1... . ()Auut16 A) ,5' -- '1
' c~,,-, / .:-'',,-': .,, . _i : ., 104..
-D - - I
3^ 6^ ae U!, OE 5t A o
Figure 4.54 Upwelling along- the Somali Current.during August, Year 4.(a) Wind-Stress, (b) Current vectors-at 37.5 mi, (c)-Upwellhng at 25i,(d) T at 37.5 mn.
-105
- -200I \I \- -- Model : t'
.-150I/\
100- / /100...........so .. ........ . ........ >5
JINA I jA O 1)'•- -50
- -
--20
/
/ -0
J IN M A Ni J J A S 0 N D
]-50
~-30
-2() .
Figure 4.55 Seasonal cycle of Somali Current surface flow at 5'N. (a)Historical alongshore flow -(solid line,after Quadfasel and Schott,1983), and maximum velocity-(dashed line) of the top-level (12.5 in) v -velocityL turing Year 4, from- s ections- at 480E-520 E. (b). Mass transportof the preva--ing flow in the 50N, 48-52E.-0-6 10-m plots.
106-
16-17 Moy40 32 38 - 36
in
0 ICO 2C
Rm
FIG. 11. Alon-horu spced in depth rance 0-600 n.. measured along L section normal to tie
coast at SN tsccton 0 in Fig. 2) during 16-17 MNa, 1979 (from Lr E-TMAA et al., 1982).
V VELOCITh LATITUDE 5.00N
480E 53OE
.............................37.. .1, 62.5
222,5 /-87.5
. 5 - 1 7.5
V k;6!0.00.0
~ '- - 4-5.0
610.0610.0
A- SEASONJAL FORCEC MO1W01"LY VEAN
CONT3Q jf ilT-iVAL r ,e.1 FIELD MIN - 21 1=. e- 12 SNISCALE .ACIOI I " ., -JELD MAX - 5Q 8 14Q SZE 12 SKI
PC2SJ =O :277Q89e-1c IrG StIM .-. 34676SIC017 ELD AREA ,8.23-7Sqt,-eCC
Figure 4.56 Somali Current cross sections-at 5'N. (a) Alongshore speedduring 16-17 M-y 1979(Schott ,1983), and-(b) mean v velocity ill the
Semtner and Chervin model during March of Year 4. "
107
. . ............ .
i' 1 1/ to
Y..*
0-.,
Fiue45 o aiC ret etrposo a 5 Yea 4 . )3.5 m
- (b 2225 n, an- (c 43.0 m
*1~~ ifi,,j108
7
0to
0 -- - ~ 0
.~lI
--- 'Ill..1i
*.'~~s** .~.. '.i 'hi
*1j *'~ 'I,:..'~ ~..-.. *
'Il/I'Ii hII*
0 ~ to
/S''' ihihUl
~' ~ itiiiJj~~ in-
I...... I lit---- 0 *,, lid
-J ii. 'ii,
* . . ~'''.IUUU I.
iI\X' ,\ ~''I~''-z'.1 U;-~
~ VI ~ hO
~T '\ __ ~, ~ I .
to - - ..~-~ ~~ '0' ii~
,,.....
hO Z
'''.. / ..
U" -~j::~.c~ .y- 4ccz.c&.~~~~.u2 ( _ -
., III.,
~
U.) ~..\ * , ~* S
~ r'"'xi
0 0 'U
Figure 4.58 Somali Curreiit vector plots of July 14, Year 4. (a) 37.5 in,-(b) 222.5- in, and- (c) 4-35.0 in.
109
.11
- , . .. . . . .
InI
- -its~ YZz
Is - td
N)
Fiue45 So al - entveto pltNfOtbr1,Ya .()3.
ml (b 2. iId 0450m
1il 10t
A
30....... .. v
I FMA.MJJASO NO J FIAMJJ)ASO NO3FA2ASNJMMJAO JFAJAONO
Year 4 Year 5 Year 6 Year 7 Ycar S
Eastward- Innsport
XWcstwatrdTransport
___ Nc i ' .Vcc rdFiovchrouch
Figure 4.60 Mass transport in the Indonesian Archipelago. Compiled frommonthly mean tapes i Years-4-8. at 117.5 0E.
22-
21-
20-,
S14-
I I M A NI J J A 5 0 N 1)
Figure 4.61 Seasonal cycle and interannual variability of Pacific-IndianOcean tlirouglillow at 117.50E. Years 4-8-are-superimposed-onthe mean.
1-12
CASEA 4001 ITERATION 10409PARALLEL OCEAN CLIMATEr MODEL (P0CM) 1/2 DEG WORLO OCEAN NO1. 2
U VELOCITY LONGITUDE 11 7.501-30S 20S los 0
6100- 610.0847.5 -4.
1 11600- 1160.0
w1975.0 -- 1975.0
_ 2475 0k-U 2475.0
-3C25. 0- 30 25. 0
3575.01 - 3575.0
4600.0 nanO.
SCALE FACTCR = -W FIELD M~AX. 67-6 t9.03S.'2.5m)
POSSLI -022017CE10 m! -. 405113E 0 FELDAdnEA ag.4478414E-It
Figure 4.62 Zonial section at 1117.5 0E, -used to calculate througli-flow.Thc figure-illustrates uvelocity in August, Ycar4. Althouzh there aresignificant flows in each dirction, the' net westward mass transport is16.4 Sv.
113
CASEA 4001 ITERATION 1070-1PARALLEL OCEAN CLIMATE MODEL (P0CM) 1/2 DEG WORLD OCEAN NO, 3
TEMP ERATURE LEVEL 12.50M-
40E 60E BOE IOOE 120E
2ON- 26 N
IA0-~ 26 F
% 29
N77
203-= 2~~ 0
40E 6OE SOE IO0E 120E
A- I/2DEG ROBUST OIAG,FREE THERMSEAS CYCLECONTOUR INTERVAL = 1.0 FIELD IN = 0 a l9Q75.29.759)
SCALE FACTOR = 1,12 FIELD MAX z 29.4 1119, 75F. 11255)
SEA5LACEMrEA1VF
~ C,
252
.2 2t
Figure -5.1 Comparison of January T at 12.5 mn with climatology. (a-)Monthly-mean temperature in the model, and (b)-Hastenrath and Lamb
- (1979) sea surface temp-erature.-j
'114
CASEA 4001 ITERATION 10702PARALLEL 0' N CLIMATE MODEL (POCNO 1/2 OEG WORLD, OCEAN NO. 3
TEIMPERPATURE LEVEL 12.50tv
40E 60E 80E bCOE 120E
20N- -.20NI
0- 0
/ 21 --
270
20S-' 2624
J7 2 0 2&
40E 60E 80E IOOE 120E
A- 1/20EG ROBUST DIAG,cREE THERMV,SEAS CYCLE
CONTOUR 11:7ERVAL z 1.00 CIELD MIN = 21 1 (107 2SC.29 75S)SCALE FACTOR z 20 FIELD MAX z 29 3 1214 7q85.0,75S2
- .7'j 2~ \CESChart 51 1
v 'ZIz
25
272V
Figure 5.2 Comparison of February T at 12.5 mi with climatology. (a)Monthly mecan temperature in the model, and (b) 1lastenrath and-Lamb(1979) sea -surface temperature.
115
CASEA 4001 ITERATION 10703PARALLEL OCEAN CLIMATE MODEL (P0CM) 1/2 DEG WORLD OCEAN NO. 3
TEMPERATURE LEVEL 12-50M -
40E 60E SOE IOOE 1-20E
~ 22N
0 00
... ...1 2 3
77
27 2720S - 2'-f2 6',,' 20OS
25'
40E 6CE 80E IOOE 20A- 1/20EG ROBUST DIAG,FREE TIIERM,SEAS CYCLE
CONTOUR IN8TERVAL = 1,03 PIZLO t4IN = 21.3 1106,25E,29 759)SCALE FACTOP % 0 ''2 FELD MAX - 20 190 75E.1.251
5 A tVFJACE II.% Chart P
25k ------ /
" 2 23
Figtire~ 5.7oprsno2ac t125mwt ciaooy a
Motl ia eprtuei h oe-?n-()Hsert nLm
(197 se-srfc tempera2ure.
116,~1
CASEA 400 1- TR A TI1ON 10704PARALLEL OCEAN CLIMATE MODEL (P0CM) 1/2 DEG WORLD OCEAN NO. 3
TEMVPERATURE LEVEL 12.5OM
40OE 60E 80E 1OOE 120E
20N - ~-20N
288
01j 29 2
2272
2 0 S- _ _S
26- '22
-~ 2
40E 6oE 80E IOOE 1C
A- 1/2OE1G ROBUST DIAG,FREE THEzRM,SE=AS CYCLE
CONTOURl 11TERVAL = 1.00 FIELO MIN z 20.9 1131 7=E 20 75S)SCALE FACTOR a 1.00 FIELO MAX = 0 6 139 7SE.4.75SI
7 I ~ ~ I Chart 53 ~
-~22A
2129
22
Figure 5.4 Comparison of April T at 12.5 m wvith cfin-atology. (a)Monthly mean temperature in-the model, and (b) 1-astenrath and Lamb
- (1979) sea surface temperature.
117
CASEA 4001 ITERATION 10705
PARALLEL OCEAN CLIMATE MODEL (POCM) 1/2 CEG WORLD OCEAN NO. 3
TEMPERATURE LEVEL 12.50M
40E 60E 80E )ODE 120E
20N- 20N
0- - 0
29
20S 20S
3 523
40OE 0E 0E;OC I120E
A- 1/2DEG ROBUST DIAG,FREE THERM,S:AS CYCLE
CONTOUR INTERVAL = 1.00 FIELD HIN = 20 6 1102.7E.2Q 75SI
SCALE FACTOR = 1.00 FIELD NAX - 32.9 132975E.4.75S)
~ ~2 - LA t~1A~C tI~~h~Chart
,-J '_>.-LL>-. - i-.
--:L -. .
" { ":--ZZ,
Figure 5.5 Comparison of May T at 12.5 mn with climatology. (a)Monthly mean temperature in the model, andf(b) I-astenraith and Lamb
(1979) sea surface temperature.__
-18
CA SEA 4001 1TERATION 10706PARALLEL OCEAN CLIMA7E MODEL. (P0CM) 1/2 DEG WOR~LD OCEAN NO. 3
TEMPERATURE LEVEL 1 2.50M4E60E BCE 1OOE 120'a
20N-2'- .1 - - j-20 N
a23 20 2-20 0
7- I0
I 5 27
20S2 -20
40E 60E 80E bCEF 2,0EA- 1/2DEG ROBUST DIAG,FREE-= THERV,SEAS CYCLE
CONTOUR LlJTERVAL = .00 F1LO MIN x P 7 150 75E.D.75N1SCALE FACTOR = 1.00 FIELO MlAX % 30,4 (39 75=4.7q?;
SEA 5S.'FACE 7EXChart 55
27 27<'
U?~.~ 9
L P
~C
-Figure 5.6 Comparison of Junec T at 1-2.5 rn with- climatology. (a)Monthly -mean temperature in the model, and (b) Hastenrath and Lamb(1979) sea surfaceltemperature.
119
CASEA 400i ITERATION 10707DARALLEL OCEAN CLIMA7TE M!ODEL (P0CM) 1/2 DEG WORLD OCEAN NO. 3
TEMPERATURE LEVEL 12. $ DM
40E 60-C B0E 100E 120E
01 i 2O
- 27
- 26
20 S 20S
40C 60Es0E 100 120--
A- 1/2DCEG R0BLVST DIAG.FREE THERIV,SEAS CYCLE __
SCALE MA1 ~ b~O~ED1AX z 20 7 106 7 C, 5.24
S~r~t1~t~AI~rChart 56
1/K'
. . . . ......
Figure 5.7 Comparison of July T at 1-2.5 -nm with climatology. (-Mon~thly mean temaperature in the-model-, and-(b) Hastenrath and Lamb(1979) sea surface- temperature.
120
CASEA 41001 ITERATION 10708
PARALLEL OCEAN CLIMATE MODEL (P0CIMt s/2 DEG WORLD OCEAN-NO. 3
TEMPERATURE LEVEL 12.501A
40E 6OE DOE lOOE 120E
2 01 N -20N
2?
1 29 29 j25 27
27 -8
-~J7-I I-2
20S0ElDE10A- /OEGROBUT OAG.?EE 1-IRMSAS YCL
A-12~E OUS l-fE- THRSA CYLEc1',nAr
37 . ,4 , Chart 57
2t
227
-42 #
2.2
Figure 5.z5 Comparison of August T at 12.5- m- with- climatology. (a)-Monthly mean -temperature in the model, and--(b) 1lastenrath and Lamb(1979) sea surface temperature.
CASEA 4001 ITERATION 10709
PARALLEL OCEAN CLIMATE MODEL (P0CM) 1/2 DEG IWORLD OCEAN NO. 3
TEMPERATURE LEVEL I 2.50M
40E 60E 80E IOOE 120E
20IN- 120A2
I ~27
I- 2e
0- 9 8 9 0
205.]
20S- -24 2;D __20
A- 1/2DEG ROBUST DIAG,FREE THERM;-SEAS CYCLECONTOUR INTERVAL = 100 FIELD MIN 16J 152 75EA3.2511)
SCALE FACTOR 1.00 FIELD MAX - 29 4 19 75c- 1. 7SWJ
[a ___ 30 chart 58 ~
.2 25
Figre5-.9 omprionof epembr at125 Wvi clmtloy aMonthly ~ ~ ~ ~ I mea teprtr2n h oean b atnr adLm
1 12
CASEA 4001 iTERATI0N 10710PARALLEL OCEAN CLIMATE MODEL (P0C.M) 1/2 DEG WORLD OCEAN NO. 3
TEMPERATJ!PE L-VEL 1O3M
60E 80E OE 120E
20N- -20N
S 27
01 27
C~C/
2~
IIt
4CE GOE SC
Fiue51 CNTOURso oNERA October T at 12.5 16 F- ~ 1 l03 atology. (a)MonALy mAnO teprz r in - Mhe moel ad I=Hatnrt and.2Lamb
(1979 seaJC surfaceit Iemperrture
12
CASEA 40O01 ITERATION t0711
PARALLEL OCEAN CLIMATE MODEL (P0CM) 1/2 DEG WORLD OCEAN NO. 3
TEMP ERATURE LEVEL 2.50MV
40E 60E B0E )DOE 120E
2 ON] -20N
01 22
0 -2 -
203 2 20S
2S
40E 60E 80;r 16OE 120E
A- 1/2DOEG ROBUST DIAG,FREE THERM,SEAS CYCLE
CONTOUR ENTERVAL = LCD FIELD MIN = 27 4 199 25E.2q 75S)SCALE FACTOR i.D FIELD HAX - 29.5 1131 255-TE-3.253)
SE A LFLCE rwTEMRATEZ, 4.- Chart 60
.~ V.-
2
Figure 5.11 Comparison of November T at 12.5 m-with climatology.(aMonthly mean temperature in the model, and (b) Hastenrath and Lamb(1979) sea surface temperature.
124
CASEA 4001 ITER;ATION 107 12
PARALLEL OCEAN CLIMATE- MODEL (P0C M) /2DEG WORLD OCEAN NO. 3
TEMPERATURE LEVEL 1-2.50M
40E 60E SOE I DOE 1120E
20N -20N
I ~ 27 U.
~ ~ 27
22520S- 20S
40E 6OE'E E 120E
A- u/2OE-G ROBUST DIAG,FREE THERIV,SEAS CYCLE
CONTCJR INTERVAL = .00 FIELD MIlN = 19 2 11" . 2SC. 29 25S I
SCALE ;:ACTOR - 1.23 FIELD MAX x 29 7 174 -2=r 13 75N)
nI '~ Char', 61.4
:7-
Figure 5.12 Comparison of December T at 12.5 mn with climatology. (a)Monthly mean temperature in the-model, and (b) Flastenrath and Lamb(1979)-sea surface temiperature.
125
Indian Ocoon Rvorogo Voloc-llos: Jor.20t11 -20
"1 . ..'$ .. . ...... AS, '
all .. 7 4, % -loll
.. . . . . . . . . .
11s .. .. -
EsO . ,. .. .... ...... ;..... . .......... .. .\. .. . . .,. .... ". . s
:/ ;/ : , : ... ..... ... .... . ..... ,...... ,
IDS - - o* M I'
Si xs ........ -Su
EO EC): ~
5S .. .. SSI
40E ASE SCtE SSE 60E 6SE 7E 75E HEC SSE 92C 95C 120E ICSE
Indlon Ocoon Alvorogo Vo-1-oclt-los: mor
517 ..........J.-/
l * '~ . - '* , *€ % *)
- "
I I 1,. ... ......
40C ASE S6tE SSE 60 6 5r 79E 7SE e0E SSE 90C 9SE MeE ICA(
Figure 5.13 Drifting buoy-derived near-surface currents in the IndianOcean during January, February, and March. (Molinari e al.,
- 1990).
126
Indfll Ocoas flVorcigo VeoIfItoss: apr
~ :15
EO- EO ,
* -~ *1 -7-
Indian Ocoon fiverogo Vo Ior;I tIos: nov
l; : - -
4 Al s
S .I~--------
-----
4S! / ' SS 62 fS M M CC : 'Z A M C
-nlnOnr A-00c S 4- .7.ef JJu
--- A A *
4-t;2N~~w~
IG E
t rdtr
125--- .A-- -.-
42f ~ ~ ~ ~ A, 4S 52 $'r St 6E 2 * i Ir le r
Fiuure~~~~~~~~~~~~~** 5.4Difn I-ehdna-sraecre nteIda
Occan~~ ~ ~ ~ duigArl aadJn.(oiar a,19)
1271
IndI on Ocean flveroge Ve-laci-flis: Jul2011 --- N il
's" ~ ~ His~I=-*
... .. .. ..-.
a.~ ~ ...**,
EO -I I aE0A I
ED~~~ - . ar.-aM ., ')
........... . I ....N~~~.a ' .a...\- . . ..*
40E 4SE SOE SSE 6CE 6SE 703E 7SE GOC OSE 9CE 9SE I ME LOSE
Indian Ocean Aiverage VelocilieS: QUO2011 2014- -- ~--------
1511- 1-~- Sra
101 .... ... ..* . . .. . ... o r
EO ED
255 25540E ASE SOE SSE 60E 65E 70E 755 80E 855 90E 955 100E 2055
Indian Ocean Fiverago Velocities: Se1p2011 .aa-----i- -- - 2011
E -- -. . .I.. . . ... a . ? % ~ j aX'. ' )
a a ~ a ~ 2, ~ ~ \;~a t.
a 4.
40E 4SE SOE SSE 60E 6SE 70C 7SE OCE 8SE 90E 95E 10CE IlOSE
Figure 5.15 Drifting buoy-derived near-surfa-ce currents in the IndianOcean- during July, August, and September. (Molinari- et al.,1990),
128
Indlon Ocoon Avorogo Volocltl-os: oct2011 21;
aa \ a 1i f * *
t i .I.l. . . . . 101'
,. * .... ... - - -- . . ,,
S - .... 5...... . .... . -
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Figure 5.20 Mass transport at 901E.
133
100-
90' February SEC
80~ NEC
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70-,
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"0 50-
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30-'
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Longitude
Figure 5.21 Variation of mass transport with longitude in February ofYea r 4.
134-
100--
90- July SEC
80- NEC
70- -SIAC
C 60---
-~50-
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Figure 5.22 Variation Of mIass transport with longitude ini July of Year4.
135
(a)
1361
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