1. Interannual Variability (Indian Ocean Dipole) P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS) Indian Institute of Science (IISc) Bangalore 560 012 vinay@caos.iisc.ernet.in Summer School on Dynamics of North Indian Ocean June-July 2010

2. Outline What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics IOD Impacts

3. The Unique Indian Ocean

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

6. Measure of IOD : Dipole Mode Index DMI=SSTA West -SSTA East West = 50°E-70°E;10°S-10°N East = 90°E-110°E;10° S-0° Vinayachandran et al., 2009

7. Positive IOD

8. Negative Dipole

9. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics IOD Impacts

10. Seasonal Evolution: Ocean

11. Seasonal Evolution: Atmosphere

12. October 2006 Anomalies SST (shaded) winds (vectors) winds (vectors) and OLR (contour) and OLR (contour) Indian Ocean Dipole Events

14. QSCAT Wind Anomalies for 2006 APR MAY JUNSEP OCTDEC

15. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics IOD Impacts

16. SSTA : Model – GISST Comparison Vinayachandran et al., DSRII, 2002

17. Base code GFDL MOM4, 30S-30N; 30E – 120EBase code GFDL MOM4, 30S-30N; 30E – 120E Horizontal resolution: 0.25º X 0.25ºHorizontal resolution: 0.25º X 0.25º 40 Vertical Levels, 5m resolution in the top 60m40 Vertical Levels, 5m resolution in the top 60m Horizontal mixing: Chassignet and Garaffo (2001)Horizontal mixing: Chassignet and Garaffo (2001) Vertical mixing: KPP (Large et al., 1994)Vertical mixing: KPP (Large et al., 1994) Forced by daily dataForced by daily data High Resolution Indian Ocean Model Wind stress Wind speed, air temperature, humidity Incoming shortwave and longwave radiation, Chlorophyll Rainfall and river discharge

18. 1.Climatology: 7years, forced by OMIP (based on ERA-15 reanalysis), SeaWiFS chl, CMAP Rainfall and SAGE river discharge. 2. QSCAT RUN: QSCAT Winds, SeaWiFS Chl, TRMM Rain and NCEP (Radiation, Ta, q), 19 July 1999 onwards. Model Experiments Vinayachandran et al., GRL, 2007

19. Dipole Mode Index Standard deviation of DMI:Model = 0.42; TMI = 0.53

20. SSTA : Model – TMI ComparisonJuly September October

21. MSLA : Model – Altimetry ComparisonJuly September October

22. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics IOD Impacts

23. Mixed Layer Heat Balance (East) : 1993-98 Heat flux Entrainment Advection

24. Mixed Layer Heat Balance (West) : 1993-98 Heat flux Entrainment Advection

25. Murtugudde et al., 2000, JGR 75-85E, 5S-5N 95-105E,10S-Eq. Mixed Layer Heat Balance (anomalies) : 1997-98

26. Upper Ocean (50m) Heat Budget: 2006 EAST WEST

27. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics 1. Equatorial Jets IOD Impacts

28. Equatorial Jets Winds and SST May October Vinayachandran et al., GRL, 1999 Anomalies: winds and SST

29. Equatorial Zonal Winds Francis et al., Tellus, 2007

30. Equatorial Jets during IOD events

31. Impact of Equatorial Jets Hastenrath et al., 1993, JGR

32. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics 2. Thermocline anomalies, Kelvin waves and Rossby Waves IOD Impacts

33. Subsurface anomalies

34. Thermocline Anomalies & Wave Propagations

35. Observational Evidence

36. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics 3. Upwelling IOD Impacts

37. Upwelling off Sumatra Upwelling off Sumatra

38. What is Indian Ocean Dipole? Seasonal Evolution Modeling IOD Mixed Layer Processes Ocean Dynamics 3. Upwelling IOD Impacts

39. Murtugudde et al., 2000, JGR; Vinayachandran and Mathew, 2003, GRL Impact of IOD on Ocean Biology

40. Indian Ocean Dipole andMonsoon

42. Extremes of the Indian Summer Monsoon Rainfall, IOD & ENSO (period:1979-2003) Gadgil et al., 2003

43. Salinity Variations

47. Fluxes Advection Entrainment September November Processes

48. SSS Anomaly non-IOD Composite

49. Summary Indian Ocean Dipole :Dominant signal in the inter- annual variability. Coupled ocean – atmospheric phenomenon in the Indian Ocean. SST, thermocline, winds convection all take part in an IOD event. OGCMs reproduce IOD events well and illustrate the role of ocean dynamics in the evolution of SST anomalies. Unresolved issues: Triggering, dependence on ENSO, intraseasonal oscillations, impact on monsoons.

50. Thank You