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Modeling Indian Ocean Circulation

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. Oceanic Hot Spots for Monsoon. Indian Ocean Warm Pool. (Joseph, 1990). Talk Plan.

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Modeling Indian Ocean Circulation

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  1. 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

  2. Oceanic Hot Spots for Monsoon Indian Ocean Warm Pool (Joseph, 1990)

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

  4. 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

  5. Arabian Sea Mini Warm Pool

  6. 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)

  7. Warm pool : vertical structure (T)

  8. Shenoi et al., JGR, 1999 Rao et al., QJRMS 1999 Salinity Sea Level Anomaly (cm) Lakshadweep High

  9. Warm Pool : Vertical Structure (salinity)

  10. Mechanisms : Effect of Salinity Stratification Fixed Salinity (35psu) Experiment

  11. Mechanisms : Mixed Layer Heat Budget

  12. Wind Stress (Pa) Net Heat Flux (W/m2) Fields averaged over November-February period. Mechanisms : Effect of Orography and Winds What is the impact of this low winter cooling on spring warming ?

  13. 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

  14. Mechanisms : Effect of Orography and Winds SST (oC)

  15. 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

  16. Indian Ocean Dipole Figure Courtesy : FRCGC, Japan 1961, 1963, 1967, 1972, 1977, 1982, 1994 and 1997 [Yamagata et al., 2002]

  17. Indian Ocean Dipole of 2006 October 2006 Anomalies SST (shaded), winds (vectors) and OLR (contour) Vinayachandran, Kurian & Neema, GRL 2007 (in press)

  18. The IOD of 2006 • Model Simulation • Temperature equation • Processes experiments (Ocean dynamics or Air-Sea fluxes?)

  19. Experiments 1. QSCAT RUN : QSCAT Winds, SeaWiFS Chl, TRMM Rain and NCEP (Radiation, Ta, q) , 19 July 1999 onwards. 2. Process runs for 2006

  20. QSCAT Wind Anomalies for 2006 MAY APR JUN SEP OCT DEC

  21. TMI SST Anomalies for 2006 AUG JUN SEP OCT NOV DEC

  22. SSTA : Model – TMI Comparison July September October

  23. West SSTA : Model – TMI Comparison RED : TMIBLACK : MODEL

  24. East SSTA : Model – TMI Comparison RED : TMIBLACK : MODEL

  25. Equatorial Jets

  26. Upper Ocean (50m) Heat Budget : EAST

  27. Upper Ocean (50m) Heat Budget : West

  28. 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

  29. SST /EAST /Control and Processes

  30. SST /WEST /Control and Processes

  31. SST /EAST /Control and Processes

  32. SST /WEST /Control and Processes

  33. Thermocline Depth Anomalies

  34. 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

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

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