The oceanic variability in response to the monsoon system in thenorthern Indian Ocean was for the first time studied using the threealtimeters Geosat, ERS-1 and Topex/Poseidon. The root mean square,computed from the sea surface height anomalies indicates values of 15-17cm in highly energetic areas such as the Somali Current, and 13-15 cm inthe western part of the Bay of Bengal. As the most prominent variationsoccur, and because most in situ observations are from these areas theinvestigation was focused on these two areas. Complex principalcomponent analysis was applied to the gridded SSH anomalies and theresults indicate that the annual signal is strongest when the monsoonperiod is at its peak, and the semi-annual time series seems to berelated to the onset and decay phase of the SW and NE monsoon. CPCAanalysis of the Topex/Poseidon data indicates characteristic periods of40-50 days which are probably related to earlier observations in thestudy area of mesoscale variability generated by the horizontal shear inthe velocity field. Westward propagating waves are identified from theannual and semi-annual modes, and they are observed to have a westwardpropagating speed of 13 km/d at the equator, with decreasing speed awayfrom the equator. Mesoscale eddies with diameters between 250-1000 kmand maximum amplitudes up to 45 cm are observed during the monsoonperiods. The propagation and life time of eddies in the study area arein good agreement with those reported in previous investigations usingin situ, data and numerical models
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