| Satellite altimetry data from TOPEX/POSEIDON and Jason-1 were used in conjunction with a geoid from GRACE and hydrographic profiles to observe the effect of the El Nino/ Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) climatic signals on tropical Indian Ocean dynamics during the period 1993-2004. Ocean heat storage anomalies were computed from the sea surface height anomaly data using a linear regression relationship. Geostrophic currents were calculated at the surface and subsurface levels of the Indian Ocean using the beta-plane approximation near (+/-1º) the equator and the thermal wind equations elsewhere. The results of this method were validated with currents measured using Acoustic Doppler Current Profilers moored along the equator at 77°E, 83°E, and 93°E. The measured and computed currents compared reasonably well with similar features present in both. The presence of the seasonal Wyrtki Jets, the North Equatorial Current, and the Equatorial Undercurrent and their variability was observed in the estimated currents. The area-averaged heat storage anomalies were computed for two geographical boxes representing the tropical western Indian Ocean (TWIO, 55º-75ºE, 5ºN-5ºS) and the tropical southeastern Indian Ocean (TSEIO, 85º-95ºE, 0º-10ºS). This revealed a three-month lag in annual heat storage maxima during neutral ENSO and IOD conditions in the TSEIO with respect to the TWIO. The heat storage maxima co-occurred during the simultaneous El Nino/ positive IOD events in 1994 and 1997, but the lag was present during 2002. During the extreme event of 1997-1998 the positive heat storage anomalies in the TWIO doubled in magnitude while simultaneously the heat storage anomalies in the TSEIO decreased in magnitude. Time-longitude and time-depth profiles of zonal geostrophic currents at various locations were analyzed. The fall Wyrtki Jets were greatly reduced during the co-occurring El Nino/ positive IOD events of 1994 and 1997, but not in 2002. The heat storage estimates and the geostrophic currents both suggest that (1) it is the strength of the IOD signal rather than the strength of the ENSO signal than controls the weakening of the fall Wyrtki Jet and (2) there was not a positive IOD event during 2002. |
