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Satellite Altimetry for Indian Ocean Studies

MM Ali(1)

(1) National Remote Sensing Agency, Balanagar, Hyderabad 500037, India

Abstract

Satellite Altimetry for Indian Ocean Studies

MM Ali National Remote Sensing Agency Hyderabad (India)

Abstract

Satellite altimetry has given an ample opportunity to study a wide varieties of oceanographic phenomena, particularly, over the otherwise data sparce Indian Ocean region. Sea surface height anomalies (SSHA) have been extensively used to study the mixed layer dynamics and the oceanic eddies. Initially, Geosat altimeter observations have been used to infer the vertical motion of ocean waters in the equatorial Indian Ocean (EIO), in connection with the slopes in SSHA and the associated changes in mixed layer depth (MLD) slope. By analysing the SSHAs, a phenomenon similar to El Nino was observed in the EIO. However, this phenomenon of reversal of the sea level is present every year with different intensities depending upon the intensity of the southwest monsoon. Since the MLD in the EIO is dominated by the changes in SSHAs, MLD could be estimated using the altimeter observations alone and the associated changes could be studied. Similar to the atmospheric phenomena, altimeter observations could reveal a 40-60 day oscillations in the SSHAs. As a part of the ERS-1 AO project on the study of eddies, SSHAs have been estimated from GDRs and eddies were detected. Statistical analysis of the ERS-1 measurements revealed that all the corrections given in GDRs were sensitive. This experience has been used to prepare an atlas of the oceanic eddies, jointly with NOAA, from TOPEX/POSEIDON observations. The presence of eddies have been confirmed with the in situ measurements of temperature profiles. Unlike in the other parts of the oceans, Bay of Bengal eddies propagate slowly. Comparison of SSHA and the dynamic height obtained from in situ temperature and salinity profiles indicated that salinity observations were not critical for detection of eddies. Since the SSHAs represent the subsurface thermal structure, TOPEX/POSEIDON observations, in conjunction with the XBT measurements, have been used to generate another atlas of the XBT thermal structures and TOPEX/POSEIDON SSHAs, jointly with Ohio State University. This study helped to infer the subsurface thermal structure where in situ measurements are not available. SSHAs were also used to study the current variability and the inter-annual variation of eddy kinetic energy in the Indian Ocean. Statistical analysis of the SSHAs reveal that the RMS sea level variability was high in regions of Rossby wave propagation. FFT analysis was also used to identify the eddy regions. Inter-annual and seasonal variations in slope of the thermocline was studied using Jason observations in conjunction with the Argo temperature profiles.

 

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                 Last modified: 07.10.03