An oceanographic winter 2000 field program in the Japan Sea provided an unusual opportunity to examine the transformation of air as it moves from Siberia and across the Japan Sea to Japan. Measurement were made at Vladivostok, a meteorological buoy, ship and aircraft.

The ususal winter condition is that surface Siberian air is blocked from the Japan Sea by the Russian coastal mountains. Instead, the surface air reaching the Japan Sea is warmed by descent from near 1 km elevation, resulting in a small air-sea temperature difference. The moderate heat fluxes from the Sea and northerly results in the expected growth of the marine layer as it moves across the Japan Sea. Occasionally strengthening and shift of the Siberian High forms deep and very cold air over Siberia extending above the 1 km level. Northerly air in the lee of the Russian coastal mountains is 10 C colder than the coastal Japan Sea surface temperature. Although stronger heat fluxes warm the Siberian air as it traverses across the Japan Sea, the sea surface temperature strongly increases across the Japan Sea, maintaining the sea-air temperature difference and high heat fluxes. The result is semi-uniform conditions of large air- sea temperature difference and high wind for the air mass quickly traversing the Japan Sea in less than a half day. Classic cloud sheets cover the sea with individual cloud lines traceable from near the Russia Coast to Japan in satellite images. These very cold Siberian air outbreaks double the heat loss from the Japan Sea while the stronger sea surface winds and icing are significant to shipping.