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Celebrating the Monsoon Bangalore, India 7-24 2007 East Asian Monsoon In contrast to Indian monsoon Bin Wang Department of Meteorology and IPRC, SOEST University of Hawaii, Honolulu, HI 96822, USA Understanding physical processes determining the differences between IM and EAM in
Bangalore, India 7-24 2007
East Asian Monsoon
In contrast to Indian monsoon
Department of Meteorology and IPRC, SOEST University of Hawaii, Honolulu, HI 96822, USA
Understanding physical processes determining the differences between IM and EAM in
Why compare the annual variation?
JA-JF 925 hPa winds and precipitation rate (mm/day)
Circulation systems differ between Indian and EA sectors
An eastward shift of convection centers from Indian (in June-July) to the WNP (in August) during boreal summer . Peak and retreat dates differ.
WNP is the largest heat source during NH summer.
Wang, Clemens and Liu 2003
Wang and LinHo 2002
Seasonal March of
(SA Monsoontrough) and
EA Monsoon front
East Asia: 110-145E
Controlling monsoon AC?
Chang et al. 2006
In spring transition, EA sector has a well-defined extratropical precipitation band associated with the East Asian monsoon front.
In fall transition, the Indian monsoon rain retreats to the south of the equator, whereas the rain in the EA sector remains in the Northern Hemisphere.
Why compare the inter annual variation?
Observations have revealed that the year-to-year variations of the Indian and EA-WNP summer monsoons exhibit strikingly different spatial and temporal structure and teleconnection patterns (Wang et al. 2001a).
The pattern has an SIO anticyclone (AC) in the developing year of El Nino and a WNP AC in decaying ElNino. El-Nino forcing alone cannot account for: 1) the amplification of the SIO AC;or 2) the maintenance of the WNP AC. These features result from local air-sea interactions and the impacts of the annual cycle.
Leading Mode of S-EOF of 850 hPa winds and SST anomalies (1956–2004)
Wang et al. 2003 J Climate
The evolution of SIO and WNP anticyclone are not in phase with El Nino “forcing”
--Equatorial Bjerkness positive feedback (IOD/IOZM) (Webster et al. 1999, Saji et al. 1999)
--Off-equatorial Rossby Wave-SST feedback either positive or negative, depending on background annual cycle (Wang et al. 2000)
--Negative feedback by monsoon-induced anomalies (Webster et al. 2002, Loschnigg et al. 2003, Lau and Nath 2000).
--Memories of ocean mixed layer (Meehl 1994, 1997)
--Regulation of the monsoon-ocean interaction (Nicholls 1983)
--Modify monsoon response to remote ENSO (Wang et al. 2003)
Monsoon- ocean interaction is characterized by Off-equatorial moist Rossby wave –“Dipole” SST feedback (Wang et al. 2000)
The nature of this feedback depends on the basic state (monsoon annual cycle).
(Wang et al 2003)
(Wang et al. 2000)
Summer Circumglobal Teleconnection (CGT)
Ding and Wang’05
Dashed: post1979, Solid pre1979
a) The ENSO induced FV (leading mode) increases from 24% to 31% for entire AAM system
b) The second mode does not significantly related to ENSO in pre-1979 epoch but significantly leads ENSO after 1979, providing a precursor.
c) While ENSO-ISM coupling weakens, the ENSO- WNPSM and ENSO-Indonesia MNS coupling strengthens.
Increased amplitude and periodicity
Enhanced anomalous anti-Walker Cell
Increased ENSO-induced monsoon-warm pool ocean Interaction
Enhanced ENSO-Indonesian monsoon relation through all phases of ENSO
Increase in ENSO- WNPSM/ EASM relation in both Dev. & Dec. ENSO
Reduction in ENSO-ISM relation in both Dev. & Dec. ENSO
Weaken biennial tendency of the A-AM 1st leading mode
Biennial tendency and eastward propagation
Relation of the second mode and ENSO
ITCZ and subtropical monsoon front over the EA sector
How important are the East-Asian marginal seas in determining the mean monsoon structure and seasonal cycle?
· Why do the most AGCMs have great difficulty in correct simulation of the summer rainfall in the WNP and the Western Pacific Subtropical High and the Meiyu/Baiu front regions?
Why Sudden changes (singularities) at various geographic locations?
· Mmechanisms for 10-20 day and 20-60 dayvariability in the WNP region?
· What is the potential and practical predictability of the these oscillations?
· How does the air-sea interaction influence these oscillation?
· What is the coherent structure of the tropical biennial oscillation? What processes are responsible for the transition of the biennial tendency
Roles of the land surface memories. How these land surface anomalies are generated and maintained?
· What are the radiative impacts of clouds, especially cirrus, on monsoon evolution and intensity?
· To what extent the mid-high latitude circulation anomalies prior to the summer monsoon can affect the EASM? How are they generated and maintained?
H How are the teleconnection (the PJ and circumglobal teleconnection) modes associated with Asian summer monsoon excited and maintained? Are those modes intrinsic to the low frequency variability of the boreal summer mean states?
What is the predictability of the EA-WNP summer monsoon during the years when ENSO is in a near normal state?
· How does the monsoon-warm ocean interaction affect the predictability and prediction of the seasonal mean rainfall?
· What is the potential and practical predictability of the EA and WNP summer monsoon?
· What are the impacts of the ISO on the seasonal mean climate forecast?
· What is the dominant mode of the Interdecadal variation of the EA-WNP monsoons? What give rise to this variability?
· Are the interdecadal variations in the EA-WNP region linked to that over the ISM? If not how different they are and why they are different?
) From Wang et al. 2005,
Wang and LinHo 2002
Hydrological issues in RCM of monsoon: Uncertainty in moisture influxes of driving fields
Vertically integrated water vapor convergence differ by 47% between: NCEP/DOE R2 (Blue) and EAR40 (Green)
EASMI = PC1*EV1[30N-50N,110E-145E]
Regressed precipitation field
Corr. (EOF1 of rainfall, WNPMI)= -0.70
Lee et al. (2005)
Enhanced surface high
Upper-level flow anomaly
Enhanced 500hPa trough
Warm SST anomalies
Anomalous surface wind
CTRL: Climatology SST outside DTEP
MLM: Coupled GCM-Mixed layer Ocean (Alexander et. Al. 2000)
GFDL R-30 L-14
Ensemble runs: MLM16; CTRL8
Conceptual spectrum of monsoon variability on the annual to tectonic time scale. The periods of individual spectral peaks are labeled. Relative concentrations of variance at these periods are unknown. The two black peaks at the 41- and 23-ky periods indicate the Earth-orbital periods, which account for nearly all variability in incoming solar radiation.
P.-X. Wang et al. 2005
Summer monsoon index definition
Summer monsoon indices
1) Indian summer monsoon ;
All Indian Rainfall Index (AIRI, Parthasarathy et al., 1992)
Webster and Yang Index (WYI, Webster and Yang, 1992)
Monsoon Hadley Circulation Index (MHI, Goswami et al., 1999)
2) Western North Pacific monsoon ;
Western North Pacific Monsoon Index (WNPMI, Wang et al., 2001)
3) East Asian monsoon
Regional Monsoon Index (RM2, Lau et al., 2000)
WNPMI (Wang and Fan 99)
RM2 (Lau et al. 2000)