A geostrophic empirical mode based on altimetric sea surface height

Abstract

Recent discovery of low-dimensional coherent structure in oceanic currents along with a new merged altimeter product called Absolute Dynamic Topography (ADT) makes it possible to derive subsurface ocean information from satellite remote sensing data. An altimetric geostrophic empirical mode (η-GEM) is developed in this study by projecting hydrographic transects onto the ADT sea surface height coordinate, based on which the four-dimensional thermohaline and velocity structures of oceanic currents are reconstructed from satellite surface observations. In the WOCE/SR3 area, the η-GEM fields capture more than 95% of the total thermal variance. The GEM-derived flow has equivalent-barotropic structure and represents the velocity profile better than traditional dynamic modes. Comparison with mooring observations also demonstrates that the η-GEM provides good estimates of the deep thermohaline fields.