Airborne expendable bathythermograph survey of the Kuroshio Extension and comparison with simultaneous altimeter measurements during the Geosat Exact Repeat Mission

Abstract

Extensive airborne expendable bathythermograph (AXBT) sections across the Kuroshio Extension during the Geosat Exact Repeat Mission (ERM) were used to assess the ability of the Geosat altimeter to monitor the locations of the Kuroshio and its associated cold‐ and warm‐core eddies. The AXBT sections in themselves provide detailed descriptions of the Kuroshio Extension to about 160°E. These observations demonstrated that surface or near‐surface temperatures in this area may lead to incomplete and deceptive descriptions of the deeper thermal structure. Kuroshio‐eddy interactions in particular were not accurately portrayed by the near‐surface observations. For this reason, accurate mapping of the location of the Kuroshio Extension and of nearby eddies may not be practical from infrared (IR) imagery alone but requires augmentation from other measurement systems such as altimetry. In the present analysis, an estimate of the sea surface height was obtained from the altimeter ranges by time averaging sea surface heights in lieu of a geoid estimate. Sea surface height anomalies computed using the mean altimetric sea surface (i.e., the geoid plus the temporal mean oceanographic signal) can be significantly different from the actual oceanographic topography induced by mesoscale oceanographic features. Nevertheless, it is shown that the positions of the Kuroshio Extension and of the stronger cold‐ and warm‐core eddies associated with the Kuroshio Extension are easily located from these altimetric sea surface anomalies.