ASUKA Hydrographic Data Collection

Repeated hydrographic surveys across the Kuroshio and its recirculation south of Japan were carried out by a group called ASUKA (Affiliated Surveys of the Kuroshio off Cape Ashizuri) since 1992, Conductivity-temperature-depth profiler (CTD), expendable CTD (XCTD), expendable bathythermograph (XBT), and digital bathythermograph (DBT) data obtained from 155 cruises were collected for a period of 16 years, from November 1992 to May 2008. A uniform data processing was applied to raw data from the XBT and XCTD. Salinity profiles for the XBT and DBT measurements were estimated by using mean temperature-salinity relations. Biases of the salinity profiles for the XCTD measurements were estimated by using the tight relationships between temperature and salinity at temperature of 14.1 and 2.5℃, and the estimated biases were then subtracted from the salinity profiles. For the XBT and XCTD data, pressure was estimated from the inferred depth for the combined use with the CTD data. By using the integrated hydrographic dataset temporal mean volume transport of the Kuroshio and its recirculation was estimated with an assumption of zero-velocity surface at 1800 dbar.