Modeling Indian Ocean Circulation

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Modeling Indian Ocean Circulation
P. N. Vinayachandran J. Kurian
Centre for Atmospheric and Oceanic
Sciences Indian Institute of Science, Bangalore,
INDIA
Celebrating the Monsoon 24 28 July 2007
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Oceanic Hot Spots for Monsoon

• Indian Ocean Warm Pool

(Joseph, 1990)
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Talk Plan

• Arabian Sea Mini Warm Pool
• Equatorial Indian Ocean Indian Ocean Dipole of
  2006
• Bay of Bengal Fresh Water Plume
• (see poster)

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High Resolution Indian Ocean Model

• Base code GFDL MOM4, 30S-30N 30E 120E
• Horizontal resolution 0.25º X 0.25º
• 40 Vertical Levels, 5m resolution in the top 60m
• Horizontal mixing Chassignet and Garaffo (2001)
  
• Vertical mixing KPP (Large et al., 1994)
• Forced by daily data

Wind stress Wind speed, air temperature,
humidity Incoming shortwave and longwave
radiation, Chlorophyll Rainfall and river
discharge
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Arabian Sea Mini Warm Pool
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Monsoon Onset Vortex
25 May 1998
1 June 1998
1 June 1998

• Monsoon onset over Kerala in 1998 June 2

(Deepa et al., Current Science, 2007)
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Warm pool vertical structure (T)
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Shenoi et al., JGR, 1999 Rao et al., QJRMS
1999
Salinity
Sea Level Anomaly (cm)
Lakshadweep High
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Warm Pool Vertical Structure (salinity)
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Mechanisms Effect of Salinity Stratification
Fixed Salinity (35psu) Experiment
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Mechanisms Mixed Layer Heat Budget
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Mechanisms Effect of Orography and Winds
What is the impact of this low winter cooling on
spring warming ?
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Mechanisms Effect of Orography and Winds
Model Experiments NWG_Winter - WIND, air
temperature, and specific
humidity over SEAS are replaced by
mean value over Wbox during Nov-Feb
period NWG_March Same as NWG_winter, but the
forcing fields
are modified only for the month of March
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Mechanisms Effect of Orography and Winds
SST (oC)
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Conclusion
The high SST over SEAS during November-March is
because of the low winter monsoon winds. The
winds are low over SEAS due to the orographic
effect of Western Ghats.
References Kurian and Vinayachandran, J.
Geophys. Res., 2007 Kurian and Vinayachandran,
Geophys. Res. Lett, 2006 Vinayachandran,
Shankar, Kurian, Durand Shenoi, Current
Science, 2007
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Indian Ocean Dipole
Figure Courtesy FRCGC, Japan
1961, 1963, 1967, 1972, 1977, 1982, 1994 and 1997
Yamagata et al., 2002
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Indian Ocean Dipole of 2006
October 2006 Anomalies SST (shaded), winds
(vectors) and OLR (contour)
Vinayachandran, Kurian Neema, GRL 2007 (in
press)
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The IOD of 2006

• Model Simulation
• Temperature equation
• Processes experiments (Ocean dynamics or Air-Sea
  fluxes?)

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Experiments
1. QSCAT RUN QSCAT Winds, SeaWiFS Chl, TRMM
Rain and NCEP (Radiation, Ta, q) , 19 July 1999
onwards. 2. Process runs for 2006
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QSCAT Wind Anomalies for 2006
MAY
APR
JUN
SEP
OCT
DEC
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TMI SST Anomalies for 2006
AUG
JUN
SEP
OCT
NOV
DEC
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SSTA Model TMI Comparison
July
September
October
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West SSTA Model TMI Comparison
RED TMI BLACK MODEL
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East SSTA Model TMI Comparison
RED TMI BLACK MODEL
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Equatorial Jets
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Upper Ocean (50m) Heat Budget EAST
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Upper Ocean (50m) Heat Budget West
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Process Experiments

• Role of ocean dynamics (TauClim)
  Climatological winds stress,
• Role of heat flux (QClim) Wind stress for 2006,
  all others climatology
• Role of winds (WClim) Wind stress and speed
  clim, all others climatology
• Role of latent and sensible heat fluxes
  (LSClim) climatology of Ta, qa and wind speed
• Role of radiation (SWClim) climatology of short
  wave radiation
• Role of rainfall (RCLIM) climatology of rainfall

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SST /EAST /Control and Processes
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SST /WEST /Control and Processes
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SST /EAST /Control and Processes
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SST /WEST /Control and Processes
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Thermocline Depth Anomalies
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Summary

• The Indian Ocean Dipole of 2006 is well simulated
  by an ocean model
• Oceanic process had the dominant role on the cold
  SST anomalies in the east.
• In the west, air-sea fluxes lead to warm SST
  anomalies

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Acknowledgements

• INCOIS, DOD (Ministry of Earth Sciences) for
  funding
• BOBMEX, ARMEX Programs, DST
• GFDL for MOM4 source code, Ferret for graphics

Thank You