Collinear analysis of altimeter data in the Bering Sea

Abstract

Eighteen months of sea surface height data from the GEOSAT altimeter along collinear subtracks were analyzed for information on the circulation pattern in the Bering Sea. Seventy subtracks from both ascending and descending orbits, with as many as 35 repeat cycles along each subtrack, were analyzed. Orbit errors were removed from the height data using a least-squares fit to a cubic polynomial, weighted by the inverse of the height variance. Addition of the weights decreased contamination of residual height profiles by the large geoid signal. Composite maps of variability along each track revealed patterns of increased variability in the regions of the documented Bering slope current (BSC) and the proposed western boundary current (WBC); however, no evidence was found of the expected bifurcation of the BSC near the Siberian coast. Past observations of tides in the Bering Sea were reviewed along with a local tide model to detect tidal contributions to the mesoscale sea surface height variability. The tidal analysis suggested that residual tides contributed primarily to the longer wavelengths which were removed in the collinear processing. Examination of the Schwiderski tidal correction proved it to be a sensible correction, reducing the height variance by approximately 60%. Finally, using a Gaussian model for the BSC velocity profile, synthetic residual heights were generated and fit to the actual data to produce estimates of absolute surface geostrophic velocity and transport. Comparisons of mean flow, height fluctuations and seasonal trends across the BSC, the WBC and Bering Strait support the hypothesis that the BSC turns north at Cape Navarin into the WBC which, in turn, is capable of supplying a major part of the transport through the Bering Strait.