Observational data from the Arabian Sea Monsoon Experiment (ARMEX-Phase IIA) in the southeastern Arabian Sea
(SEAS) showed intense warming with the SST up to 31.5°C during April-May 2005. Analysis of 5-day repeat cycles
of temperature and salinity profiles from an ARGO float (ID No. 2900345) in a 3°x1° box closer to ARMEX-II buoy
(8.3°N, 72.68°E) in the SEAS during January-September 2005 revealed evolution of warm pool (SST>28°C) in spring
2005. The Argo data derived D20 (depth of 20°C isotherm) showed the influence of remote forcing during January-May, and local wind forcing during southwest monsoon. Low salinity waters (<34.0) occupied the top 30 m during
January-February followed by temperature inversions (up to 0.5°C) in the 30-60 m depth range. From the peak spring
warming, the SST dropped gradually by 3.5°C by end-July with the advent of southwest monsoon followed by a
decrease in net heat gain upto 100 W/m^2. The merged weekly products of sea surface height anomalies and the NLOM
simulated surface currents showed complex surface circulation consisting of seasonal Lakshadweep High/Low in
winter/summer. The examined oceanic and atmospheric variables showed an intraseasonal variability with 41 to 63 day
period, coinciding with the Madden-Julian Oscillation.
The merged ERS-1/2, TOPEX/Poseidon and Jason-1 altimeter weekly sea level anomalies (SLAs) for the period 1997-2005 were analyzed to study the variability of sea level and computed geostrophic currents in relation to the equatorial jets in the Indian Ocean. Year-to-year-variability in SLA was large (small) at 77°E (93°E) with a pronounced (weaker) semi-annual variation. The computed geostrophic currents, using the second order differential equation, in the equatorial region (2°S-2°N) revealed the existence of spring and fall equatorial jets in each year, but with considerable variation. The 9 year mean (excluding 1997-98) SLA and the derived currents revealed that spring (fall) jet was weak (strong) with higher (lesser) magnitudes of SLA in the eastern basin. The computed surface currents agreed well with the Acoustic Doppler Current Profiler (ADCP) measured currents and OGCM for Earth Simulator (OFES) simulated currents. The interannual variability of the equatorial jets revealed that the fall jet extended for longer duration than the spring jet. The equatorial Kelvin wave with a wavelength of ~1100 km was identified. Westward propagating Rossby wave was identified at 5° N more clearly. The zonal currents at 5° N (south of Sri Lanka) revealed intense anticyclonic (cyclonic) eddy activity between 75° and 80° E during summer (winter) monsoon.