The mean velocity field of south Indian Ocean has been derived by combining high resolution maps of sea level anomalies and the surface drifter data from the Global Drifter program from 1993 to 2012 with a resolution of 1/3 × 1/3 degrees in latitude and longitude. The estimated mean velocity field exhibits strong western boundary currents, zonal currents and eastern boundary currents. The Agulhas Current shows a velocity of above 1.5 m s -1 at around 35°S. The distribution of energy associated with the fluctuating motion and the mean flow illustrates that mesoscale variability are particularly relevant in the Mozambique Channel, south of Java and around 40°S. Advection of mesoscale features along the western boundary is evident in the distribution of eddy fluxes. The long-term average monthly surface velocity field exhibits large variations in surface currents. The most change is observed in the South Equatorial Current which shows spatial and temporal variations.Key words: South Indian Ocean, Circulation, Currents, Satellite altimetry, Surface drifter Citation: Benny, N. P., D. Ambe, K. R. Mridula, S. Ses, K. M. Omar, and M. R. Mahmud, 2014: Mean and seasonal circulation of the South Indian Ocean estimated by combining satellite altimetry and surface drifter observations. Terr. Atmos. Ocean. Sci., 25, 91-106, doi: 10.3319/TAO.2013.08.05.01(Oc)

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The present study analyses the mean and seasonal mesoscale surface circulation of the Northern South China Sea (NSCS) and determines the influence of El Niño/Southern Oscillation (ENSO). High resolution Eulerian velocity field is derived by combining the available satellite tracked surface drifter data with satellite altimetry during 1993-2012. The wind driven current is computed employing the weekly ocean surface mean wind fields derived from the scatterometers on board ERS 1/2, QuikSCAT and ASCAT. The derived mean velocity field exhibits strong boundary currents and broad zonal flow across NSCS. The anomalous field is quite strong in the southern part and the Seasonal circulation clearly depicts the monsoonal forcing. Eddy Kinetic Energy (EKE) distribution and its spatial and temporal structures are determined employing Empirical Orthogonal Function (EOF) analysis. The ENSO influence on NSCS surface circulation has been analyzed using monthly absolute geostrophic velocity fields during 1996-1999.