Dynamic topography of the Bering Sea

Abstract

[1] A new mean dynamic topography (MDT) for the Bering Sea is presented. The product is obtained by combining historical oceanographic and atmospheric observations with high-resolution model dynamics in the framework of a variational technique. Eighty percent of the ocean data underlying the MDT were obtained during the last 25 years and include hydrographic profiles, surface drifter trajectories, and in situ velocity observations that were combined with National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) atmospheric climatology. The new MDT quantifies surface geostrophic circulation in the Bering Sea with a formal accuracy of 2–4 cm/s. The corresponding sea surface height (SSH) errors are estimated by inverting the Hessian matrix in the subspace spanned by the leading modes of SSH variability observed from satellites. Comparison with similar products based on in situ observations, satellite gravity, and altimetry shows that the new MDT is in better agreement with independent velocity observations by Argo drifters and moorings. Assimilation of the satellite altimetry data referenced to the new MDT allows better reconstruction of regional circulations in the Bering Sea. Comparisons also indicate that MDT estimates derived from the latest Gravity Recovery and Climate Experiment geoid model have more in common with the presented sea surface topography than with the MDTs based on earlier versions of the geoid. The presented MDT will increase the accuracy of calculations of the satellite altimeter absolute heights and geostrophic surface currents and may also contribute to improving the precision in estimating the geoid in the Bering Sea.