Celebrating the Monsoon

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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
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• Understanding physical processes determining the
  differences between IM and EAM in
• Annual cycle
• Interannual variability
• Interdecadal variability of ENSO-monsoon relation
• Issues remain to be addressed

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Annual Variation

• Why compare the annual variation?
• Indian and East Asian (EA) monsoon subsystems are
  driven by different lower-boundary thermal
  forcing associated with land-ocean configuration
  and topography.
• Examination of the different characteristics of
  the annual variability of the two subsystems may
  provide useful insight to understand how tectonic
  forcing and solar orbital forcing affect monsoon
  circulation.

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Asian-Australian Monsoon System
JA-JF 925 hPa winds and precipitation rate
(mm/day)
EA-WNP sector
Indian sector
Circulation systems differ between Indian and EA
sectors
Fig. 1
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Seasonal Distribution of rainfall
WNPM
IM
EAM
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
Fig. 2
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(Climatology 1979-2001)
Rainy Season
7/11
9/15
7/01
6/21
6/11
7/11
6/01
7/01
6/11
5/21
6/21
6/01
8/10
7/20
5/21
5/11
6/01
5/01
6/15
5/21
4/21
5/11
Wang and LinHo 2002
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Indo-China 100-110E
Seasonal March of ITCZ (SA Monsoon trough)
and EA Monsoon front
East Asia 110-145E
Indian monsoon 70-95E
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How important is land-sea contrast and orography
in Controlling monsoon AC?
Chang et al. 2006

• Marked cross-equatorial flows in the South China
  Sea and Celebes. Annual cycle of the Australian
  monsoon has a firmer link to the EA monsoon than
  to the Indian monsoon.
• Active convection and rainfall region shifts from
  Indian sector in boreal summer to the EA sector
  in austral summer

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Equinoctial asymmetry
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.
April
October
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Differences in the annual cycle

• Meridional extent and circulation systems
  tropical system vs. coupled tropical and
  subtropical system (EA)
• Seasonal march of major heat sources BOB and WNP
  heat sources behave differently.
• Rainy season onset and peak
• Strong EA winter monsoon more closely coupled to
  Australian summer monsoon
• Equinoctial asymmetry.
• The differences in the annual cycle are
  attributed to the effects of differing land-ocean
  configuration on atmospheric response to the
  annual solar forcing, which resembles the effects
  of the external (tectonic and orbital) forcing on
  paleo-monsoon variability.

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Interannual Variation

• Why compare the inter annual variation?
• Are factors that determine annual cycle of
  monsoon also operate on interannual time scale?
• Study of the different response and feedback of
  the Indian and EA monsoons to ENSO and warm pool
  conditions would shed light on the paleo-monsoon
  variability over the South China Sea and over the
  Arabian Sea.

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How circulation corresponds to anomalous monsoon
heating
ISM
WNPSM
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Anomalous Monsoon Circulation and Teleconnection
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).
ISM
WNP- EA SM
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What give rise to the differences between
interannual variations of the EASM and ISM?

• For the Indian monsoon, strongest anomalies occur
  during the fall of the El Niño developing year,
  while for the East Asia monsoon, the strongest
  anomalies occurs in the spring after the El Niño
  years.
• What are the leading mode of IAV of the A-AM
  system?

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S-EOF1 mode of A-AMS interannual variability
Leading Mode of S-EOF of 850 hPa winds and SST
anomalies (19562004)
Wang et al. 2003 J Climate
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The evolution of SIO and WNP anticyclone are not
in phase with El Nino forcing
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Factors determining the IAV

• Remote forcing from El Nino/La Nina
• Monsoon-warm pool ocean Interaction
• --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 annual cycle (indirect role of
  continent)
• --Regulation of the monsoon-ocean interaction
  (Nicholls 1983)
• --Modify monsoon response to remote ENSO (Wang
  et al. 2003)

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Monsoon-warm ocean interaction

• 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)
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Connections between ISM and EASM Summer
Circumglobal Teleconnection (CGT)
Ding and Wang05
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Conclusions

• The factors that control monsoon intensity may be
  classified as two groups The forcing external to
  the coupled atmosphere-ocean-land system
  (tectonic forcing and solar orbital forcing) and
  the forcing internal to the coupled climate
  system, such as (remote) El Nino/La Nino, local
  monsoon-ocean interaction, land-atmosphere
  interaction and extratropical influences (ice or
  snow cover).
• The mechanisms operating on the annual and
  interannual time scales are dominated,
  respectively, by the external and internal
  forcing.
• The differences between the Indian and East Asian
  monsoon is essentially determine by the relative
  strengths of the external versus internal
  forcings.

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Conclusion (Cont.)

• The robust coupling between the East Asian and
  Australian monsoon on both the annual and
  interannual time scales is essentially
  established by tectonic forcing. Thus, the
  increase in solar procession could enhance both
  the Indian summer monsoon and the East Asian
  winter-Australian summer monsoons.
• El Niño has little influence on the Arabian Sea
  summer monsoon, but considerable impacts on the
  South China Sea monsoon (about 10 on average and
  40 in strong events), suggesting that drastic
  changes in the Pacific thermal conditions could
  remarkably alter the East Asian-Australian
  monsoon intensity.

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Interdecadal variation of the ENSO-monsoon
relationship

• What are the differences between EASM and ISM?
• What causes these differences?

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• ID Changes of Regional monsoon-ENSO relations
• ISM-ENSO relationship weakens in both developing
  and decaying ENSO
• WNPSM-ENSO relation strengthened in both phases
• Indonesian monsoon-ENSO relationship strengthened
  in all phases of ENSO.

Dashed post1979, Solid pre1979
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Observed changes in the major modes

• The overall coupling between the A-AM system and
  ENSO has become strengthened in post-1979 period.
  
• 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.

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Changes in ENSO behavior in late 1970s
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
Reduction in ENSO-ISM relation in both Dev.
Dec. ENSO
Increase in ENSO- WNPSM/ EASM relation in both
Dev. Dec. ENSO
Weaken biennial tendency of the A-AM 1st leading
mode
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Conclusion

• Two major modes of IAV of AAM system (1956-2004).
  The first has prominent biennial tendency and
  concurs with ENSO turnabout. The second leads
  ENSO by one year.
• The origin of the first mode is attributed to
  three factors Remote El Niño forcing, the
  monsoon-warm pool ocean interaction, and the
  influence of the annual cycle.
• The monsoon--ocean interaction is characterized
  by off-equatorial Convective coupled Rossby
  wave-ocean ML interaction.

• IDV of the major modes
• Biennial tendency and eastward propagation
• Relation of the second mode and ENSO
• Overall coupling between the A-AM system and ENSO
  has become strengthened since 1980.
• The IDV is attributed to increased magnitude and
  periodicity of ENSO and the strengthened
  monsoon-ocean interaction.

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Issues

• How to define the domain of EASM?
• How to measure the intensity of the EASM? Modern
  vs. Paleomonsoon
• Interpretation of the intensity change of the
  EASM in orbital time scale (An 2000, Ding et al.
  1995, Yancheva et al. 2007)

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Questions

• (1) What are the major patterns of interannual
  variability in the entire EA-WNP summer monsoon
  region (0-50N, 100-140E)?
• (2) How do these patterns link to mid-latitude
  and tropical circulation anomalies?
• (3) What processes give rise to these major
  patterns of variability?

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EA-WNP Summer monsoon system
ITCZ and subtropical monsoon front over the EA
sector
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Conclusion

• The leading mode (38 of total variance)
  represents enhanced precipitation along the EA
  subtropical front, primarily associated with
  decaying phases of El Ninos (and after 1990 its
  reversed pattern links to developing phase of El
  Nino).
• The response of the EASM to El Nino and La Nina
  forcing is nonlinear.
• The second mode (11.3 of the total variance) is
  associated with developing phases of the El Nino
  and La Nina events and the third mode (7.4 of
  the total variance) links partially to the NINO4
  warming.
• Major modes are determined primarily by
  monsoon-warm pool ocean interaction, remote
  forcing from El Nino and NINO 4 SSTA.
• The teleconnection patterns are dominated by a
  north-south tropical-polar teleconnection.

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Conclusion

• Meiyu/Changma/Baiu is anticorrelated with WNP
  ITCZ. Whether this anticorrelation exists on
  multi-decadal to orbital time scale deserves
  further study.
• Recommendation a strong EASM be defined by
  abundant Meiyu/Changma/Baiu.

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Any comments?
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Index Reference Defining variable(s),level (hPa) and regions Correlation with PC1 and PC2 Correlation with PC1 and PC2 Combined skill ()
Index Reference Defining variable(s),level (hPa) and regions PC1 PC2 Combined skill ()
IGQY Guo 1983 SLP, (1050N,110160E) -0.34 0.49 12.6
ISZ Shi and Zhu 1996 SLP, (2050N,110160E) 0.02 0.70 8.3
IPSN Peng et al. 2000 F, 500, (1050N,110150E) 0.25 0.63 12.2
IZZ Zhao and Zhou 2005 SLP, (3050N,110160E) -0.01 -0.78 8.9
IWY Webster and Yang 1992 u, 850, 200, (1040N,110140E) -0.57 -0.40 16.6
IWDJ Wang et al. 1998 u, 850, 200, (515N,90130E) -0.86 -0.15 20.0
IZHW Zhu et al. 2000 u, 850, 200, (010N,100130E) SLP -0.55 -0.51 17.4
IHSX He et al. 2001 u, 850, 200, (010N,100130E) -0.89 0.04 19.3
IWF Wang et al. 1999 u 850 (532.5N,90140E) -0.97 0.06 21.1
IHY Huang and Yan 1999 F, 500, (2060N,125E) -0.38 -0.08 8.9
ILKY Lau et al. 2000 u 200 (2050N,110150E) -0.38 -0.39 12.3
IZTC Zhang et al. 2003 u 850 (1035N,110150E) -0.93 -0.03 20.1
IWN Wu and Ni 1997 v, 850, (2030N,110130E) 0.56 -0.02 12.2
IWWO Wang et al. 2001 v 850 (2040N,110140E) 0.69 0.28 17.8
ILZ Li and Zeng 2002 u, v, 850, (1040N,110140E) -0.93 0.03 20.0
IQCZ Qiao et al. 2002 u, v, 850, (2040N,110140E) 0.81 -0.20 14.0
IWHJ Wang 2002 u, v, 850, (2040N,110125E) 0.70 -0.14 16.3
IJQC Ju et al. 2005 u, v, 850, (22.532.5N,112.5135E) OLR 0.59 0.14 14
ILZh Li and Zhang 1999 divergence, 850, 200, (7.517.5N,105125E) 0.44 0.05 9.8
ILC Lu and Chan 1999 v, 1000, (7.520N,107.5120E) -0.51 0.12 12.1
ILWY Liang et al. 1999 u, v, 850, (520N,105120E) OLR -0.89 0.10 19.8
IDXZ Dai et al. 2000 u, v, 850, (520N,105120E) -0.93 0.07 20.7
IWL Wu and Liang 2001 u, v, 850, (520N,105120E) OLR -0.35 0.23 10.0
IYQ Yao and Qian 2001 moisture PV, 850, (1020N,105120E) 0.06 -0.42 12.7
IZLY Zhang et al. 2002 u, v, 850, (520N,105120E) OLR -0.57 0.21 14.5
ILJP Lee et al. 2005 precipitation, (2050N,100180E) 0.67 0.32 17.8
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Conclusion

• The leading mode of the EA-WNP summer monsoon
  represents enhanced precipitation along the EA
  subtropical front, primarily associated with
  decaying phases of El Ninos (and after 1990 its
  reversed pattern links to developing phase of El
  Nino).
• The response of the EASM to El Nino and La Nina
  forcing is nonlinear.
• Major modes are determined primarily by
  monsoon-warm pool ocean interaction, remote
  forcing from El Nino and NINO 4 SSTA.
• The teleconnection patterns are dominated by a
  north-south tropical-polar teleconnection.
• Meiyu/Changma/Baiu is anticorrelated with WNP
  ITCZ. Whether this anticorrelation exists on
  multi-decadal to orbital time scale deserves
  further study.
• Recommendation a strong EASM be defined by
  abundant Meiyu/Changma/Baiu.

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. ISSUES     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?
    
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ISSUES (CONTINUE) 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? Interdecada
l variability      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,
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P52-55
P40-42
P34-36
P30-32
P40-42
P41
P34-35
P40-46
P44-46
P52-53
P52-56
P34-35
P30-33
P34-35
P30-33
Wang and LinHo 2002
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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)
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Definition of EASMI
EASMI PC1EV130N-50N,110E-145E
Regressed precipitation field
Corr. (EOF1 of rainfall, WNPMI) -0.70
Lee et al. (2005)
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cold AC
A
Warm
A
Sinking motion
Enhanced surface high
Upper-level flow anomaly
Enhanced 500hPa trough
Reduced convection
Warm SST anomalies
Anomalous surface wind
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• Mechanism for the establishment of WNP AC
• (i) El Nino enhances upper troposphere
  subtropical ridge and deepen the East Asian
  trough, encourage northward recurved tropical
  storms
• (ii) The vigorous tropical-extratropical exchange
  of air mass and heat enhances the EA cold air
  outbreak into Philippine Sea
• (iii) ISO and associated positive air-sea
  coupling further facilitating the abrupt
  establishment of the WNP AC
• (iv) Cold SSTA in the WNP precondition the
  establishment of WNP AC
• (v) Anticyclonic vorticity advection from the SA
  to Philippines.

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Experimental design (Lau et al.)
CTRL Climatology SST outside DTEP MLM Coupled
GCM-Mixed layer Ocean (Alexander et. Al. 2000)
GFDL R-30 L-14 Ensemble
runs MLM16 CTRL8
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Time scales of monsoon variability
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
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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)