Observations of Upper Ocean Hydrography and Currents in the Japan Sea Using PALACE Floats Researchers Stephen C. Riser, University of Washington Dr. Steve Riser University of Washington School of Oceanography Box 357940 Seattle, WA 98195-7940 Phone: (206) 543-1187 Fax: (206) 329-0858 riser@ocean.washington.edu Award Number N00014-98-1-0182 Objectives This research studies the circulation and hydrography of the upper 800–1000 m of the Japan Sea over at least a few complete seasonal cycles to understand the process of mixed-layer formation and destruction there. In some ways the Japan Sea behaves as a subtropical ocean, and in other ways it is more like a subarctic one; as a result, it is a useful laboratory for studying many oceanographic processes that occur throughout the world ocean. Approach Thirty-six PALACE floats were deployed in the western Japan Sea during the summer of 1999. These floats were deployed from the Russian research vessel Professor Khromov, from the FERHRI laboratory in Vladivostok. The floats cycled between the sea surface and 800 m depth at approximately 7-day intervals and collected profiles of temperature and salinity during their ascent phase on each cycle. All results are available in real-time via the ARGOS system and web page. Results The absolute geotrophic flow maps can be used in a variety of studies of the Japan Sea circulation. The coverage of the data is best in the western Japan Sea, north of about 30 degrees N, and the seasonal structure of the western boundary currents in this region has been well-elucidated by this method. The data show that the circulation is strongest in winter, with two clearly formed gyres (an anticyclonic subtropical gyre and a cyclonic, subpolar gyre), separated at about 39 degrees N, at all levels of the water column above 800 m. In the summer, the circulation is much weaker, and the southern gyre is nearly nonexistent in this region. The flow is strongly surface intensified. At deeper levels, there is a single deep boundary current extending from the coast of Russia south along the N. Korean coast. In the eastern Japan Sea, the eastern branch of the Tsushima Current is strongest at the surface, especially in winter.