- 33 -

B. ATMOSPHERIC CIRCULATION ÄBOVE AFRICA

H. FLOHN, J.-O. STRÜNING

l. Infcroduction

Shortly after arriving 1799 at South America, Alexander von

Humboldt - then thirty years old - climbed the Silla Moun-

tains near Caracas and described his vivid impressions of

the dense rainforest which was so much different from the

arid cactus scrub he had encountered at Margarita Island

just off the coast. After a brilliant career he laid one of

the foundations of scientific climatology by Publishing

(1817) the first primitive isothermal map. As a world-famous

far-sighted prince of science he proposed (1842) a model of

theoretical climatology including the general atmospheric

circulation. Not before about 12o years later serious attacks

towards such a model were made by Smagorinsky, Mintz, Leith

and others.

Even now, our empirical knowledge of the large-scale circu-

lation is mainly derived from latitudinal averages, disre-

garding the fact that in the northern hemisphere the tropos-

pheric temperature differences along latitude circles reach

more than So percent of those between equator and pole due

to the different heat budget of oceans and continents. The-

surprisingly large asymmetry between the hemispheres -

caus'ed by the strongly contrasting heat-budgets of the Arc-

"•fcic Ocean and the Antarctic Continent - has been discussed

elsewhere (1).

- 34 -

2. Atmospheric Heat budget

These regional heat budget differences - äs outlined by

Albrecht, Budyko, J. S. Malkus, and Seilers (2-5) - are

responsible for the different circulation patterns above

tropical oceans and continents (6). The pceanic pattern is

represented by the central'Pacific and the western Atlantic,

where below 800 mb the trades frora the two hemispheres seern

to clash in a single (or double) ITC (Intertropical Conver-

gence Zone) with its differentiäted structure, and where at

15o - 3oo mb the upper tropospheric westerlies from the two

hemispheres are either merging or separated by quasiper-

sistent vortex cells (7). The continental pattern is found

above the section Africa - Indian Ocean - Indonesia where

the low-level ITC splits into two distant branches separa-

ted by a broad zone of equatorial westerlies, and where the

extratropical westerlies of both hemispheres are permanently

separated by a broad belt of high-tropospheric easterlies.

In this section, large seasonal displacements of the flow

patterns in a meridional direction produce the well-known

tropical and subtropical monsoon wind belts (8, 9). This

system of tropical monsoons is not restricted to the coastal

zone between Asia and the Indian Ocean - äs outlined by most

textbooks since Halley (1686) and Woeikof (1874) - but is

similarly developed above the continent of Africa singely.

The main difference between the heat budgets of the conti-

nental and oceanic sections is the role of the sensible heat

flux U from the ground into the air, which contributes,

above the tropical continents, between aboüt 80 and more than

2oo Ly/d but only 2o - 4o Ly/d at tropical oceans (6). It

must-be stressed, however, that the heat budget of an equa-

torial rainforest is not substantially different from that

of a tropical ocean. The equation of the heat budget of the

atmosphere (for sensible heat) can be v/ritten äs follows:

- .35 -.

~ = UT + L - P - div (svh) - QTQ.T1 Jj Jj

h = c • T — enthalphy

h = / P h dzJz >->

L = heat of condensation (assumed constant)

P = precipitation

div (vh) = divergence of the transport of sensible heat*

The first term is the vertical divergence of U_, being the

sensible heat that a vertically integrated column of air

gains from the surface of the earth.

L • P = latent energy gained by a column of air frorn the

condensation of l g water vapour per unit of time

-> L J Wdz = L - Pz

where

W = net amount of condensating water vapour in an air

column

The fourth, term is similar to the first. Here, however, we

are dealing with the vertical radiation flux.

rJ aivv QL az =

Q_ is the net short and long wave radiation absorbed (or±jemitted) between the top and the bofetom of an air column.

An evaluation of the term UT can be obtained from the revisedj_iversion of M. 'J. Budykos (lo) well-known World Heat Budget

Atlas, while L • P can be derived from S. P. Jackson's -Cli-

matological Atlas of Africa (11). The radiational flux Q̂ is

now available, in principle, by combining satellite measure-

ments with radiation data froin the surface; siiailarly the»

horizontal flux of sensible heat div { wh) can be estimated',

disregarding instrumental errors, from available radiosonde

data.

- 36 -

3. Seasonal pisplacements

The sea-level pressure distribution above-Africa has been

carefully evaluated by L. Weickraann (12) for January, April./

July and October. Likewise surface winds and pressure fields

(of the low-lands only) have been presented in the meritful

atlas (13) by B. W. Thompson. In both sources the all-year .

existence of a zone of equatorial westerlies in West and

Central Afric-a - mainly in the Congo Basin - during the ex-

treme äs well äs during the transitional seasons has been

confirmed beyond any doubt. They are correlated with a rather

weak equatorial high-pressure ridge flanked by two low-pres-

sure troughs, indicating their partly geostrophic behavior.

These cyclonic belts have been defined äs the northern and

southern branches of the Intertropical Convergence Zone

CNITC and SITG), respectively. It is not intended here to

enter into a discussion of this largely ambiguous termino-

logy. Both branches can also be distinguished, in a clima-

tological sense, above the Indian Ocean - äs recognized äs

early äs 1893 by Meinardus (14) - and above the "maritime

continent" (Ramage) of Indonesia. At least north of lo°S, the

land-locked Indian Ocean is strongly affected by the influ-

ence of the adjacent continents.

This Splitting of the ITC in the continental section is cer-

tainly not accompanied, above Africa, by a sämilar Splitting

of the tropical rain-belt. From the beautiful Climatological

Atlas of Africa by S. P. Jackson (11) we can derive a repre-

servhative time-latitude section of the seasonal displacement

of the rainfall pattern along the central meridian (22°E).

The ill-defined broad axis of the tropical rain-belt is dis-

placed from about 13 S in southern summer to 13 N in northern

summer, i.e. nearly symmetrical in relation to the eguator

(Fig. 2o). • .

A similar figure (data along 32°E) has been published. inBMA 4. ' '

F ' M ' A ' M ' J ' J ' A ' S ' O ' N ' D

30°SH

Fig. 2o Seasonal Shift of Rainfall Belts (mm/month)

along 22°E

- 38 -

-10°

15°N

TrT =W

F M A M J J A S O N D J"Heat Equator" ( Max. of. Sea Surface Temp.)

"Wind Equator" (Doldruitis)

"Thunderstorm Equator" ( Max. of Thunderstorm Frequency)

"Rain Equator" ( Max, of Rain Frequency)

Meteorological Equator

Fig. 21 Annual Displacement of the Meteorological Equator at

the Central Atlantic (3o°W). Data after L. Kuhlbrodt (27)

This .contrasts well with the seasonal .displacement of the

r.ainfall belt at the central Atlantic (Fig. 21) where there

is little evidence for a frequent Splitting of the ITC,

which shifts only betwenn 1°N and 11°N, definitely asyinmetric

with respect to the equator. Similarly it does not coincide

with the seasonal shift of the NITC between about Lat. 6 N

and 23°N/ äs observed from daily w'eather maps (15, Fig. 53 -

54). If we evaluate the semi-annual contribution to the

annual rainfall for the half-years May-October and November-

- 39 -

April (not reproduced here), we obtain a good idea of the

large extension of tropical suiraner rains compared with ex-

tratropical winter rains. In addition to these cross-sections,

Fig. 22 shows the occurrence of a tropical belt of minimum

sunshine (or maximum day time cloudiness), seasonally dis-

placed only between about lo S and 4 N.

In fact we observe, near the surface, during the whole year

the occurrence of two minima of pressure, two maxima of tem~

perature (cf. p. 49} and two zones of confluent surface winds,

usually defined äs Northern and Southern Intertropical Con-

vergence Zone, respectively. The observed single broad belt

of maximum convective activity in cloudiness (Fig. 22) and

rainfall (Fig. 2o) should be correlated, at least in a sta-

tistical or climatological sense, with only one belt or mar-

ked wind convergence which produces a strong tendency for

lifting at least in the lower and middle troposphere (18).

From this evidence we should conclude that in the lower tro-

posphere only one powerful belt of convergence exists. It is

situated between the shallow surface patterns of NITC and

SITC. The convergence zones themselves apparently play only

a minor weather-producing role. )

Above Africa, the continental type of tropospheric circula-

tion has been described by Ekhart (15) and in 1959 (with

much better data) by Hofmeyr (17). In comparison to other

continents, the aerological network is here quite adäquate,

especially since 1960. B. W. Thompson (13) presents average

maps for the Standard isobaric levels. Some additional Infor-

mation on the low-level flow at extreme seasons has been'pre-

sented on earlier occasions (18) .

) A quite similar discrepancy between the position of thesurface pressure trough (equivalent to a single ITC) at theequatorial Atlantic (near 35 W) and the position of the maxi-mum low-tropospheric convergence (and lifting) has been de-monstrated earlier (H. Flohn, Beitr. Phys. Atmos., 3o, 1957,17 - 46; cf. .also Bonner Meteor. Abhandl. 5, 1965) .

Fig. 22 Seasonal Displacement of the Average Daily Dura-

tion of Bright Sunshine (h/d) along 22°E

- 41 -

Due to the large role of U_ above the tropical continents a

heat-low system develops during the extreme seasons above the

arid portions of Africa near the tropic (Lat. 23°)'of the

respective summer hemisphere. This system consists of heat-

lows be'low 800 mb, and of high tropospheric anticyclonic

cells with maxima at I5o - 2oo mb, which may or may not

slight.ly slope with height towards the equator. The lower

chain of heat-lows has been freguently defined äs the main

branch of the ITC or äs eguatorial trough in spite of its

large displacement from the eguator. It coincides with a

belt of maximum tropospheric temperatures . (.below 5oo mb)

that is accompanied by a definite decrease of temperature

towards the equator where the longitudinal temperature diffe-

rences between the ocean and the tropical rainforest of the

continent are negligibly small. From this temperature distri-

bution which is similar to that described by H. Riehl and

J. S. Malkus (19), we should expect - using the thermal wind

equation - a more or less permanent belt of shallow low-level

westerlies and high tropospheric easterlies between this

system and the "equator.

If the concept of 'a seasonal displacement of this heat-low

system (ITC) across the equator is correct in substance, and

if the liberation of latent heat of condensation in the "not

towers" (19) of the rainfall areas acts äs the main source

of energy of the tropical Hadley cell, then we have to ex-

pect during the trarisltional seasons a position of this

system near the geographical equator itself. Under such con-

ditions the low-level westerlies and the high-level easter-

lies should disappear, especially if we take into account

that in the immediate vicinity of the equator (say below 5

Lat.) the thermal wind equation is hardly valid. In this

case we should expect a combination of low-level easterlies

and high-tropospheric westerlies, similar to those in several

oceanic cross-sections.

- 42 -

4. Zonal Wind Systems and Temperature Pattern

To check this simple model it would be of little value to

investigate the temperature field above the African conti-

nent since the horizontal temperature differences are in the

upper troposphere of the sarne order of magnitude (l - 3 ) äs

the instrumental .errors of the different radiosonde types

involved. Since the number of radiowind stations in tropical

Africa is larger than those of radiosondes, it was decided

to construct monthly meridional cross-sections of the zonal

upper winds along the longitudinal belt with the greatest

number of available ascents i.e. at 32 E (Fig. 6 - 17).

While Jahuary and July (Fig. 6, 12} confirm Hofmeyr's results

(17) - averaged over Africa without regard to longitude ~,

in the transitional months April (Fig. 9) and October (Fig.

15) the belt of upper easterlies still exists in the lati-

tudes o - lo N. There is little indication of low-level

westerlies at 85o mb/ which are, however, found between sur-

face and 9oo mb in the central African section. It should be

stressed that similar results are obtained along loo - llo°E

and - at least at 2oo and 7oo mb - above most of the Indian

Ocean (2o).

The essential points of this description can be demonstra-

ted by two time-latitude sections. Here the 85o mb-level

(Fig. 23) for the lower troposphere and the 15o mb-level

(slightly above 14 km) for the high troposphere IFig. 24)

have been selected. As shown in the maps of surface pressure

and winds (12, 13), a shallow layer of eguatorial westerlies

exists even in the transitional seasons, but only in the

Congo Basin west of 3o E and mainly restricted to the levels

below 9oo mb. Along the cross-section across eastern Africa

(5 N - 5 S), the layers below 85o mb are orographically much

disturbed and must, therefore, be omitted from the discussion.

Te.

Sal.

2Q"-Bul.H

L.M.

„. Dur.

Fig. 23 Meridian-Time Cross-Section of Resultanfc 85o mb-Winds along 32 B (3 = Q:5o

1 »10*20-30 "iO »50 • 50 *60 »70

S J F M A M J J A S O N D

Fig. 24 Meridian-Time Cross-Section of Resultant ISO mb- Winds along

45 -

Nevertheless the occurrence of low-tropospheric "equatorial

westerlies" during the extreme seasons {December - March,

June - September) at 'the respective summer hemisphere is

verified by the data (Fig. 23). At the equator itself they

persist annually önly west of Long. 3o E below 9oo mb, here

orographically blocked by the mountain areas around the cen-

tral African rift (18) . As indicated by Hofmeyr (17), they

extend at the southern hemisphere to higher levels (65o -

7oo mb, 5 - 16° Lat.) than at the northern hemisphere (always

below 75o mb, 2 - 2 2 Lat.). This may be due to the higher

elevation of the surface, 12oo - 18oo m, äs compared with

2oo - 4oo m in the Sudan. Near 2l°N the equatorial wester-

lies from the southwest converge, in this section, with a

north-northwesterly flow, which originates in the well-known

Etesians in the eastern Mediterranean. In this area (Nile

Valley - Red Sea, cf. p. 28) a large-scale northerly flow -

produced by the strong latitudinal surface pressure gradient

between the Azores High (Io23 mb) and the monsoonal heat-

lows of Arabia, Iraq, and especially the Punjab (997 mb) -

lifts the generally easterly flow of this latitude from the

surface. West of 2o E it rotates clockwise to NE in a diver-

gent pattern.

At the level of their smallest extension near 15o mb, the

high-tropospheric__easterlies (Fig. 24) can be followed per-

manently throughout the year, however, with varying width,

intensity and constancy. During northern summer they extend

from 27 N to at least 12 S, with a maximum speed of about

5o knots near 15 N. Here we find, between mid-June and early

September, the exit area of the Tropical Easterly Jet (21) ,

where wind maxima of 80 - llo knots are occasionally ob-

served: this is one of the most constant and permanent

currents of the global atmosphere. During southern summer a

weaker "easterly Jet" develops above south-central Africa,

centered around lo S. In the transitional months, like April

and November (Fig. 16), the easterlies are substantially

- 46 -

reduced to the zone 2 S - 8 N o r o - 6 N / in both cases re-

presented by the data of Bangui with a constancy of only

3o - 4o percent. This low constancy indicates occasional

disturbances/ äs is usual at the boundary between easterlies

and westerlies. However, the prevalence of easterlies shows

that the concept of a coincidence between thermal and geo-

graphical equator during the transitional seasons is un-

realistic; at least this coincidence should be restricted

to periods of not more than about lo days. Assuming that

geostrophic conditions are at least gualitatively valid near

5 Lat. (C. E. Palmer and Coll. (22) have found evidence for

such quasi-geostrophic behavior) a tropospheric temperature

maximum seems to exist, even during this season, somewhere

near 7 N, with a small temperature decrease towards the

equator. The seasonal displacement of the circulation patterns

is delayed for about two months compared with the sun's

zenithal position.

To check this concept, the meridional temperature gradient

during the mid-season months has been evaluated for the layers

85o - 7oo, 7oo - 5oo, 5oo - 3oo, and 3oo - 2oo mb by the

thermal wind equation (Fig. 25, 26}. Here the winds of En-

tebbe/ äs biased by diurnal sea-breeze circulation, have not

been used, also due to their position only 6 km off the equa-

tor.

T = average virtual temperature of the layer 3p

R^ = gas constant of dry air, f = 2-fi. sinf

P = pressure in an average level

—-*• = change of the geostrophic zonal wind component in the

p layer dp

-tu

Fig. 25 Meridional Temperature Distribution (derived from

the Thermal Wind Equation: Teraperature Gradient

/Qy (degr./l°°o km)), Januaxy and April

3er

Fig. 26 Meridional Temperature Distribution, July and

October

Because of the small difference between ihs. v.i ftu-al and the

actual temperature, it will be referred only to meridional

temperature gradients, -which, when directed to the north,

will be considered äs positive.

The results for the lower troposphere are guite clear and

convincing: in each month the highest temperatures occur

twice, once in each hemisphere outside of the equatorial

region, and enclose a slightly cooler area just north of the

equator. This distribution coincides well/ for January and

July, with the results of radiosonde ascents (17). The posi-

tion of the wärmest region shifts between 18 S (January) and

27 N (July), äs is suggested by our simple model. In the

upper troposphere, however, two temperature maxima are ob-

served only during July (near 27°N and 8°S), while in the

other months only one maximum exists.

5̂ Interpretation and Conclusions

Any Interpretation of these results must be based on the

budget eguation for sensible heat h, where the first two

terms U_ and L • P are easily evaluated (Fig. 27). ünfortu-LJnately, regional (and seasonal) quantitative data for the

last two terms, the divergence of the sensible heat trans-

port and the net absorption (or loss) of radiatlon, are not

yet available. However, first-order estimates of the sign

can be based on the average vertical and meridional wind

components of the Hadley cell and on cloud distribution. In

the lower layer, the coincidence of warm regions with high

UT and of cool equatorial air with small U_ is quite evident,jj jjIn the upper troposphere the highest temperatures seem to

coincide in most seasons (except northern summer) with the

precipitation belt which furnishes large amounts of latent

heat. Since most condensation heat should be liberated in

20*N 10° 0" 10' 5 20° 20°N 10°

Fig. 27 Heat Budget Data along 32°E

10° S 20'

- 51 -

the lower troposphere, the average lifting in the ITC-region

may be responsible for the upward transport of this energy

source. In addition to this/ we may expect highest radiatio-

nal absorption (QT<o) in the humid äquatorial atmosphere

with its high cloudiness, äs indicated by the results of

Hanson et al. (23) and, according to Möller (24), at the

gray-radiating layer between loo and 2oo mb. The slight meri-

dional displacement of the temperature maximum poleward from

the rainfall maximum (January towards south, April and Octo-

ber towards north) can be interpreted äs caused by an average

meridional transport of latent heat due to the Hadley cell.

During July the position of both high-tropospheric heat cen-

ters cannot be understood from such considerations: at 27 N

the significant high-tropospheric mass-convergence (21) to-

gether with strong subsidence (adiabatic warming) may con~

tribute significantly to the dominant role of input of sen-

sible heat. During this season the Hadley cell is situated,

from the kinematical point of view, in the right position,

however contrary to the usual thermo-dynamical sense, i.e.

with sinking warm air and rising cool (eguatorial) air, and

thus acts äs a work-consuming cell (6, 21) .

From all these regional patterns we first have to visualize

that during the whole course of the year above Africa the

thermal eguator never does coincide with the geographical

equator except during short periods on the order of a week.

In the lower troposphere two- heat sources exist outside the

humid belt near the equator (where high evaporation and

cloudiness suppress strong heating). These sources are cen-

tered above the semiarid or arid parts of the continent

where maximum values of UT are found. In the upper tropo-jjsphere a broad maximum of temperature only slightly displaced

poleward from the position of the rain belt can be observed.

If we take into account the average vertical and meridional

transport of heat done by the tropical Hadley cell, it may

be considered that the release of latent heat in the equa-

- 52 -

toria.1 rainbelt is the main heat source of the upper tropo-

sphere, similarly äs in the oceanic ITC region, äs reflected

also in the results of Riehl and J. S. Malkus (19) on the

temperature pattern near the ITC. In the lower troposphere,

however, the different heat budget of humid and arid (or at

least seasonally arid) continental areas causes a Splitting

of the thermal equator into two heat maxima separated by a

cool equatorial area: this in turn produces the large-scale

Splitting of the ITC with all its dynamical conseguences.

Instead of a gradual displacement, the main heat center -

identical with the primary ITC at the respective summer

hemisphere - vacillates seasonally between the two hemi-

spheres, according to the sun's zenithal position.

The heat budget of the equatorial rainforest belt with its

high evaporation E - L • E takes about 9o percent of the net

surface radiation - and cloudiness resertibles much more an

ocean than an arid continent. This is reflected in the tro-

pospheric temperature distribution. It would be interesting

to obtain reliable radiosonde data from the only arid con-

tinental area at the eguator itself: that of northeastern

Kenya and southern Somalia.

With its relatively complete data coverage, Africa is more

than only a representative example of a tropical continent.

It may also serve äs a speculative model of the circulation

pattern to be expt;cted at a homogeneous land-covered globe

with a hydrological cycle.

Appendix: After completion of this lecture it has been

realized that several maps sind diagrams published recently

in the USSR (26, cf. Fig. 18 - 21, 25) present a quite in-

dependent verification of our results.

- 53 -

References

1) Flohn, H.: Ann. Meteor. N. F. 3, 76 - 80 (1967);

Bonner Meteor. Abh. 7, 3 - 7 (1967)

2) Albrecht, F.: Wiss. Abhandl. Reichsamt f. Wetter-

dienst 8, 2 (1941); Z. f. Meteor. 2 (1949),

129 - 143; Ber. Dt. Wetterdienst Vol. 66

(I960), 79 (1961), 83 (1962), 99 (1965)

3) Budyko, M. J.: Teplowogo balanssa zemlii, Leningrad

1954

4) Malkus, J. S. in M. N. Hill, The Sea, Vol. I,

88 - 294 (1963)

5) Seilers, W. D.: Physical Climatology. Chicago 1965

6) Flohn, H.: Proc. Symp. Tropical Meteorology Rotorua,

N. Z. 1963, 16o - 172; Geogr. Rundsch.

12 (196o), 129 - 142, 189 - 195

7) Riehl, H.: Tropical Meteorology. London - New York

1954

8) Chromow, S. P.: Isv. Vsesoi. Geogr. Obshtsh. 82

(I95o), 225 - 246

9) Flohn, H.:" Ber. Dt. Wetterdienst US - Zone 18 (195o) ,

34 - 52

10) Budyko, M. J.: Atlas Teplowogo Balanssa Zemnogo

Schara. Moscow 1963, 69 p.

11) Jackson, S. P.: Climatological Atlas of Africa,

Lagos - Nairobi 196112) weickmann, L. jr.: Meteor. Rundsch. 16 (1963),

89 - 100

13) Thompson, B. W.: The Climate of Africa. Oxford Uni-

versity Press 1965, 132 p.

14) Meinardus, W.: Arch. Dt. Seewarte 13 (1893), No. 7;

cf. H. Flohn, Z. f. Meteor. 7 (1953), 97 -

lo8

15> Garnier, B. J.: Weather Conditions in Nigeria. McGill

Univ., Climatological Research Series 2

(1967)

- 54 -

16) Ekhart, E.:

17) Hofmeyr, W.

18) Flohn, H.

19) Riehl, H.,

20) Frost, R.,

21) Flohn, H.:

22) Ballif, J.

23) Hanson, K. ,

24) Möller, F. :

25) Flohn, H.:

26) Lebedeva., A

Forsch, Erfahr. Ber. Reichswetterdienst A lo

(1941)

L.: Notos (Pretoria) lo (1961), 123 - 149

in Tropical Meteorology at Africa, Nairobi

I960, 253 - 267; cf. also Bonner Meteor.

Abhandl. 5 (1965) and 6 (1966)

J.- S. Malkus, : Geophysica (Helsinki) 6 '(1958),

• 5o3. - 538

P. M. Stephenson; Proc. Symp. Tropical Mete-

orology Rotorua, N. Z. 1963, 96 - Io6;

cf. also C. R. V. Raman, C. M. Dixit:

lo7 - 118

Bonner Meteor. Abhandl. 4 (1964)

R., C. E. Palmer, P. C. Sinclair and W. Viezee:

An Empirical Study of Air Movement near the

Eguator, University of California Los An-

geles, Final Report Contract AF 19 (6o4) -

2134, August 1958

J., Th. H. Von der Haar, V. E. Suomi; Monthly

Weather Review 95 '(1967), 354 - 362

Lecture presented at the Caracas Conference,

November 1967

Bonner Meteor. Abhandl. 5 (1965) ; Erdkunde 19

(1965), 179 - 191

N., 0. G. Sorotshan: Klimaty Afriki. Lenin-

grad 1967, 486 p.

27) Kuhlbrodt, E.: Forsch. .Erfahr..Ber. Reichswetterdienst

A 15 (1942)

- 55 -

List of Figures

Fig. l Distribution of Stations

Fig. 2 Time-Altitude Cross-Section Malakal

F.ig. 3 • " Nairobi

Fig.. 4 "• Dar-es-Salaam

Fig. 5 " . Lilongwe

Fig. 6 - 1 7 Meridional Cross-Sections of Zonal Winds along

32 E', January - December

Fig. 18 Yearly Cycle of the Zenithai Position of the

Sun, Maximum of Rainfall, Maximum of Easterlies

and Westerlies

Fig. 19 • Cross Circulation in the TEJ (after BMA 5)

Fig. 2o Seasonal Shift.of Rainfall Belts (mm/month)

along 22°E

Fig. 21 Annual Displacement of the Meteorological Equa-

tor at the Central Atlantic (3o°W) . Data after

L. .Kuhlbrodt .(1942)

Fig. 22 Seasonal Displacement of the Average Daily Du-

ration of Bright Sunshine (h/d) along 22°E

Fig. 23 Meridian-rTime Cross-Section of Resultant 85o mb-

Winds along 32°E'

Fig. 24 Meridian-Time Cross-Section of Resultant 15o mb-

Winds along 32°E

Fig. 25 • Meridional Temperature Distribution (deriVed

.from the Thermal Wind Equation:. Temperature'ä T

Gradient v/oy (degr./looo km) ) , January and

April

Fig. 26 Meridional Temperature Distribution, July and

October

Fig. 27 Heat Budget Data along 32°E