Oceanic surface geostrophic velocities determined with satellite altimetric crossover method

Abstract

If the Coriolis force is balanced by the pressure gradient in the hydrostatic equilibrium. the ocean current is referred to as the geostrophic current Most ocean currents worldwide are approximately geostrophic currents The surface geostrophic velocity is calculated with the satellite altimetric crossover method in this paper The uncertainties of geostrophic velocity determined from satellite altimetric crossover data are analyzed If the accuracy of the sea surface slope along the ascending or descending track of altimetric satellite is up to the 10(-7) level with 50 km of resolution, the geostrophic velocity will have an accuracy of better than 10 cm/s In the areas of low latitude or near the altimetric satellite orbital inclination, the uncertainty of geostrophic velocity determined with the crossover method will be much bigger than that in the low-/mid-latitude areas The Kuroshio area east of Taiwan, China is selected as a testing region A highly accurate and up-to-date geoidal model which is determined using the combined data from the ground-based gravimetry, ship-borne gravimetry, air-borne gravimetry and satellite altimetry, is selected as the reference geoid Sea surface heights from the geophysical data records of TOPEX/Poseidon and Jason-1 from 2002 to 2005 are used to compute highly accurate dynamic heights at three crossover points Geostrophic velocities are then derived at these crossover points and are basically identical to the current velocities provided by the National Center for Ocean Research, Taiwan, China