Satellite altimeter derived geostrophic currents in the western tropical Pacific during 1992–1993 and their validation with drifting buoy trajectories

Abstract

TOPEX/POSEIDON satellite altimeter measurements from the western tropical Pacific (15°S–20°N, 125°E–165°W) are used to make monthly sea surface topography maps for the period October 1992 to October 1993. The altimeter data were processed using standard corrections to estimate along‐track sea surface height anomalies which were interpolated to monthly 1/10° resolution maps. To convert these surface height anomalies to absolute sea surface height, a 0/1000‐dbar mean seasonal dynamic height climatology was computed from the same input data used by Levitus (1982) to compute his dynamic height climatology, with less spatial smoothing. By adding the appropriate monthly altimeter heights to these seasonal means, we produce 12 approximately monthly sea surface topography maps from 36 cycles of altimeter data. The corresponding monthly geostrophic surface currents were compared with the tracks of nearly coincident satellite‐tracked drifting buoys and were found to agree well in most cases. The velocity components (zonal and meridional) were plotted separately with respect to the velocities estimated from the buoy positions, and correlations of these two data sets are very high. The seasonal variability of the surface geostrophic currents in this region is depicted by the monthly maps of sea surface height.