Formation mechanism of Japan Sea Proper Water in the flux center off Vladivostok

It is known that wintertime air‐sea interaction in the Japan Sea, enhanced by outbreaks of dry and cold air masses from the Eurasian continent, generates a characteristic water mass called Japan Sea Proper Water (JSPW) through deep convection. Using NASA scatterometer (NSCAT) wind vectors with high spatial resolution of 25 km, the role of the wind field over the Japan Sea in JSPW formation was investigated during the period of winter monsoon. It is revealed by NSCAT observations that the wintertime surface winds over the Japan Sea are strongly influenced by the upstream topography of the coastal region of the Eurasian continent. A strong wind area appears off Vladivostok, both in the snapshot and the monthly mean wind fields. The dynamics behind this strong wind flow may be attributed to the highly stratified surface wind being blocked by the coastal mountains and exiting through the narrow valley near Vladivostok into the Japan Sea. The NSCAT winds are coupled with European Centre for Medium‐Range Weather Forecasts air temperature and humidity and Japan Meteorological Agency sea surface temperature (SST) data for turbulent flux estimation. Monthly mean wind speed, momentum flux, sensible heat flux, latent heat flux, and evaporation have peak values exceeding 9 m s−1, 0.275 N m−2, 170 W m−2, 130 W m−2, and 120 mm, respectively, in the strong wind area, which has a diameter of about 150 km. Multichannel sea surface temperature (MCSST) images of the Japan Sea for late January 1997 show that the cold SST (∼0°C) area extends from the coastal region to the outer sea off Vladivostok. The MCSSTs decreased by 1°C for January in this region. The cold SST region coincides with the strong wind area, and both locations agree well with the JSPW formation region, which, according to Sudo [1986], is north of 41°N between 132° and 134°E. The spatial agreement strongly suggests that the wind, enhanced by the topographic effect around Vladivostok, causes the large turbulent heat flux and evaporation in this area, which generates the coldest SST and dense water mass, i.e., JSPW. This may be a process of coastal topography‐air‐sea interaction that leads to deep‐sea water formation in the Japan Sea. Because of the concentrated feature of turbulent fluxes and the inferred relation to the center of deep convection phenomenon, the strong wind area is called the “flux center” in this study.