Airsea Interaction in the Bay of Bengal

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Air-sea Interaction in the Bay of Bengal
? Role of the ocean in developing Cyclone Nargis
Lisan Yu Woods Hole Oceanographic Institution
IOP-6 meeting June 3-5, 2009, Reunion
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Nargis Track
5/2
5/1
x
x
4/30
x
4/29
x
x
4/28

• What caused the cyclone to intensify?
• What caused the cyclone to change its direction?

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TRMM Precipitation and OAFlux Latent heat
April 27th, 2008
15N
April 28th, 2008
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Latent Heat Flux, 4/27 5/3
QuikSCAT Swath
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OAFlux estimation ofNargis latent and sensible
heat fluxes
SHF can be negative, i.e. heat is transferred
from air to the ocean
Based on QuikSCAT 12.5km swath
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Buoy SST and Tair during Nargis
Tair
SST
SST
Tair
Buoy measurements clearly show that Tair is
higher than SST during cyclone Nargis event
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SSH before cyclone intensification

• What role has the warm core ring played?
• rapid intensification?
• sustaining the cyclone strength?
• precondition of the cyclone pathway?

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SSH daily evolution 4/26 5/1
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RAMA buoy observationsT(z) and S(z) at 15N,90E
2008
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Current measurements 90E, 15N
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The anti-cyclonic circulation
Surface current climatology compiled from
drifters (NOAA/AOML)
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Schematic representation of surface circulation
(Sv)
NE monsoon
SW monsoon
Inter-monsoon
EICC East Indian Coast Current WICC West Indian
Coast Current SMC Summer Monsoon Current WMC
Winter Monsoon Current ECC Equatorial Counter
Current SEC South Equatorial Current SC Somali
Current EACC East African Coast Current WJ
Wyrtki Jet
(Schott McCreary 2001 Shankar et al. 2002)
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Warm core ring signature in SST
SST
SSH
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Summary Role of warm core ring in Nargis

• The warm core ring
• SST gt 28.5C
• the depth of warm fresh water (gt26C) greater
  than 60m

• Obvious effects
• heat and moisture source for rapid
  intensification, sustaining intensity
• Different from other cases
• The warm core ring signature is seen in SST
• ? Coupled air-sea interaction ?modulate the
  cyclone track
• Implications
• Role of dynamic topography in cyclone
  development
• ? Bay of Bengal waters are highly stratified.
  Warm core ring as an effective insulator between
  cyclone and deeper cold water?
• Better understanding of cyclone strength and
  pathway
• Predictability

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Hurricane Katrina SST and SSH
http//www.nasa.gov/centers/goddard/images/content
/148071main_Katrina_SSHeights.jpg
Scharroo et al Satellite Altimetry and the
Intensification of Hurricane Katrina. Eos,
86(40), 4 October 2005
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Was the role of warm core ring in Nargis unusual?

• Mike McPhaden told us (EOS, 2009)
• The timing of Nargis was not unusual. Nor was
  its strength unprecedented
• a category 4 cyclone hit Myanmar in May 1982
• a category 4 storm (Mala), struck Myanmar in
  April 2006.

Cyclone 01B May 1982
SSH April
Cyclone Mala April 2006