Baroclinic disturbances propagating westward in the Kuroshio Extension region as seen by a satellite altimeter and radiometers

Abstract

The Geosat radar altimeter data during the first year of its exact repeat mission are analyzed to investigate the behavior of individual anomalies of sea surface dynamic topography (SSDT) and their statistical properties in the Kuroshio Extension region. The SSDT anomalies are compared with mesoscale anomalies of sea surface temperature (SST) derived from satellite radiometer data. Remarkable baroclinic anomalies are detected in the time series of both SSDT and SST, and their westward propagation is clearly traced. The pinching‐off of a Kuroshio Extension meander at 147°E is clearly seen as the coalescence of two cyclonic anomalies which had moved fairly constantly westward without changing their relative positions. Westward propagation is statistically dominant in the SSDT and SST anomaly field. Approximate agreement between SSDT and SST anomalies suggests the baroclinic nature of the anomalies. The westward phase speed of SSDT anomalies is faster than the theoretical phase speed of the baroclinic first‐mode long Rossby wave in the upstream region of the Kuroshio Extension. In the downstream region it is consistent with the theoretical value but is somewhat faster around 35°N. In the area between 170°E and 180°, SSDT anomalies have a structure like plane waves with major axis oriented NW‐SE in the northern part and NE‐SW in the southern part. The distribution of the Reynolds stress suggests the tendency of acceleration of the mean current by those anomalies. This strong acceleration tendency at 170°E‐180° may be related to bathymetry.