Cold Air Outbreaks over the Japan Sea During Winter 2000

Clive E. Dorman, Center for Coastal Studies, Scripps Institution of
    Oceanography. (clive@coast.ucsd.edu)

Sergey M. Varlamov, Research Institute for Applied Mechanics, Kyushu
    University, Japan.

Nina A. Dashko, Far Eastern State Technical Fisheries University,
    Vladivostok, Russia

ABSTRACT:

    Synoptic meteorological conditions during the during the Winter 2000
Japan/East Sea (JES) experiment are presented.  During the winter, air
from the Siberian Anticyclone moves over China, the China Sea and Korea
to form the mean northwest winds over the central portion of the Japan
Sea. Korean topography affects the downwind sea level wind structure
well into the Japan Sea.  Fronts and cyclones usually form over China or
the China sea and move to the East- Northeast along the south side of
Japan.

    The coldest and driest air moves over the Japan sea as episodic,
cold air outbreaks occurring a minority of the time.  These are caused
by cyclones associated with upper level short waves, forming to the
southwest, moving through the Japan Sea or on the southern side of
Japan. Very cold air comes more directly from the Siberian anticyclone,
partially channeled by valleys, but descending in the lee of the coastal
mountains along the Russian coast, causing clearing.  Farther downwind,
roll clouds line up with the surface wind which is from the north or
northeast over the central Japan Sea.  An extensive and persistent
marine overcast forms on the south side of the sea due to partial
blocking by Japan's topography and a thickening atmospheric marine
layer.

    A moderate strength cold air outbreak event occurred over the Japan
Sea on 23-25 January 2000.  Strong meridional flow over the central
Japan Sea was set up by the combination of a southward movement of the
Siberian High and a strengthening of the Aleutian low. The month's
strongest winds over the central and southern portions of the Sea were
associated with this event, including freezing air temperatures.
However, rather weak surface winds were measured at Vladivostok on
account of the extreme surface stability.

    A weak cold air outbreak occurred on 19 January on the back side
(western portion) of a weak cyclone moving to the northeast over the
Japan Sea.  This event had lesser wind velocities and not as cold air
temperatures over the Japan Sea as that on 23-25 January.