View
35
Download
0
Category
Tags:
Preview:
DESCRIPTION
Variations in the Activity of the Madden-Julian Oscillation: Implications for the Southern Hemisphere Charles Jones University of California Santa Barbara. Collaboration : Leila Carvalho (USP). Outline Brief overview of the MJO - PowerPoint PPT Presentation
Citation preview
Variations in the Activity of the Variations in the Activity of the
Madden-Julian Oscillation:Madden-Julian Oscillation:
Implications for the Southern HemisphereImplications for the Southern Hemisphere
Charles JonesCharles Jones
University of CaliforniaUniversity of California
Santa BarbaraSanta Barbara
1
Collaboration: Leila Carvalho (USP)
2
Outline
Brief overview of the MJO
Example of importance of the MJO for the midlatitudes of the southern hemisphere
Outstanding issues about the MJO
1958-2006
The Madden-Julian Oscillation
Power spectrum of zonal winds at 850-hPa
o Originally discovered in early 1970’so Most important mode of tropical
intraseasonal variations o Time scales of 30 to 60 dayso Anomalies propagate eastward
along the tropical belt; phase speeds ~ 5 m s-1
o Eastern hemisphere: strong interaction with clouds, rain, surface winds and large-scale circulationo Western hemisphere: modest
interaction with convection and large-scale circulationo Significant case-to-case and
interannual variability
30-60 days
4
Modulate the variability of the monsoons in Asia-Australia, Africa and Americas
Teleconnections with extratropics in both hemispheres
Modulate thermocline variability in the tropical Pacific Ocean via westerly wind bursts; interaction with El Niño/Southern Oscillation (ENSO)
Influence on forecast skills in the tropics and extratropics
Major MJO Climate Influences
5
Madden-Julian Oscillation (MJO) Life CycleMadden-Julian Oscillation (MJO) Life Cycle
Eastward propagation of enhanced Convection
Tim
e
-15 Days
-5 Days
5 Days
15 Days
Hendon and Salby (1994)
Anomalous upper level circulation (200-hPa)
Enhanced Convection in the western Pacific
Coupled Forced Rossby-Kelvin wave response
Rossby waves
-+ -
+
Midlatitude wave train
Kelvin wave
Madden-Julian Oscillation (MJO) Life CycleMadden-Julian Oscillation (MJO) Life Cycle
7
Antarctic Oscillation (AAO) or Southern Annular Mode (SAM)
Antarctic Oscillation (AAO) or Southern Annular Mode (SAM)
One of the most important modes of weather and climate variability in the high latitudes of the
southern hemisphere
One of the most important modes of weather and climate variability in the high latitudes of the
southern hemisphere
Carvalho et al. (2005): Opposites phases of the Antarctic Oscillation and relationships with intraseasonal-to-interannual activity in the tropics during austral summer. J. Climate
8
Objective
Identify variations in extratropical cyclones properties during distinct phases of the Antarctic Oscillation
Murray and Simmons (1991) tracking scheme was applied to track storms with origin south of 50oS during summer (DJF) 1979-2000.
9
The Daily AAO Index1979-2000
• The daily AAO index: leading mode of the EOF analysis of daily anomalies of 700hPa geopotential height (H700) from Reanalysis (20-90 S).
• Positive (negative)
phases of the AAO : time coefficient of the
first EOF is greater (less) than 1 standard deviation of the DJF time series.
POSITIVE PHASE
10
Extratropical Cyclones properties – Obtained from tracking scheme based on Murray and Simmonds (1991)
Carvalho et al. 2005
Minimum PressureMaximum latitude
Life cycle duration * 12 h
AAO-AAO- AAO-AAO-
AAO-AAO-
AAO+AAO+ AAO+AAO+
AAO+AAO+
11
What are the relationships between the MJO and AAO?
12
Lag composites (Days) OLR anomalies (20-70 days)
NEGATIVE AAO POSITIVE AAO
LAG 0
LAG +5
LAG +10
LAG +15
LAG +20
LAG +25
LAG 0
LAG +5
LAG +10
LAG +15
LAG +20
LAG +25
13
Indication that onset of negative phases of AAO is associated with eastward propagation of
the MJO
14
Case to Case
Seasonal Variations
Interannual Variations
Long-term Behavior
Time scales
?? ???? ?????? ????????
Extensively studied over the years but no comprehensive theory
Behavior on time scales longer than interannual is unknown
Long-term behavior of the MJO is unknownLong-term behavior of the MJO is unknown
15
Has the MJO been more active (linear trend)?
Does the MJO have a low-frequency mode of variability (decadal)?
How will the continuous warming in tropical Indian and Pacific Oceans modify/interact with MJO?
Data• Daily U200 and U850 (1948-2006),
OLR (1979-2006)
• Subtract daily climatology; band-pass filtered (20-200 days)
• Average 15S-15N
• Combined EOF analysis (U200, U850)
• Use (EOF1, PC1), (EOF2, PC2)
• Phase angle (PC1,PC2) normalized
16
Wheeler and Hendon (2004)
MJO IdentificationCriteria:oSystematic eastward propagation
at least 1 4 oMinimum amplitude:
A = (PC12 + PC22)1/2 > 0.35oEntire duration between 30-90 daysoMean amplitude during event > 0.9o227 MJO events in 1948-2006
OLR Anomalies
We
st. H
em. &
Afr
ica M
aritim
e Co
ntin
ent
Indian Ocean
Western Pacific
1
2 3
4
7 6
8 5
17
18
Linear trends in amplitudes and number of events?
Statistically significant trends in amplitudes and number of MJO
events
19
NNR
Average 15S-15N
In progress: are linear trends in MJO activity real?
20
Does the MJO have a low-frequency mode of variability?
Low-Frequency diagram
• Consider XT, T=1, N pentads, XT=1 event, XT= 0 no event
• Define moving window SK and compute number of MJO events in SK
• SK odd number and varied from smallest (1 pentad) to largest possible N pentads)
21
0
1
2
3
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101 105 109 113 117
SK
Hypothetical Case: events evenly spaced in time
Low-frequency diagram
Cone of Influence
Cone
of In
fluen
ce
22
(a)
(b)
Figure 1. (a) Temporal variability of mean MJO amplitudes (linear trend indicated). (b) low-frequency variability of the MJO. (c) Same as in (b), but after removing linear trends. (227 events in 1948-2006)
(c)
23
Indication: MJO activity exhibits significant variations on decadal time scales
In progress: stochastic and dynamical models
Simulation with the IPRC University of Hawaii hybrid coupled model (Joshua Fu):
o Atmospheric model: ECHAM
o Oceanic model: intermediate model, tropical Indian and Pacific Oceans
o 200 years simulation
24
Figure 4. U200 anomalies phase composites from IPRC_HcGCM 200-yr simulation (782 MJOs).
Identification of model MJO as in observational
analysis
Realistic MJO simulation
Composites of U200 anomalies
25
Figure 5. Low-frequency variability of the MJO in the IPRC_HcGCM model (782 MJOs in 200-yrs).
Low-Frequency variations of the MJO200-yr model simulation
Summary
MJO exhibits significant linear trends and decadal variations
reanalysis is affected by changes in observational sampling; impact in MJO characterization is unknown
26
www.icess.ucsb.edu/asr
Work in ProgressDeveloping stochastic and dynamical model experiments to investigate trends and low-frequency variations in the MJO Investigating warming in the tropical Indian and Pacific Oceans and their impact in the activity of the MJO
27
Real time monitoring and forecasting of the MJO
www.icess.ucsb.edu/asr
28
www.cdc.noaa.gov
Recommended