East Asia Coastal Cyclone

The ability to predict the behavior of large storm systems is an important and
necessary tool for helping save lives and property that can be lost during
severe weather events. The MM5 numerical model is used here to simulate the
structure and evolution of an East Asia coastal cyclone that occurred in June
of 1993.This is the case of an extratropical cyclone which initiated in eastern
China and deepened rapidly when it moved to the Yellow Sea. The pressure at the
cyclone center dropped 12 mb within a 12 hour period (1200-2400 UTC June 1).
Strong gales and heavy precipitation associated with the storm caused severe
weather in China, Korea, and Japan.

The iso-surfaces of potential temperature and equivalent potential temperature
show a cold and dry air mass coming from northeast China, which caused the
frontal genesis and the baroclinic development of the cyclone. Vertical cross
sections display the cold front's shift southward and the warm front's movement
northward.

The relative vorticity development accompanied the cyclone deepening. The
iso-surface of relative vorticity exhibits two parts. The lower part of the
vorticity was related to the cyclone and the cold front. The upper part of the
vorticity is related to the upper level trough and the jet stream. The
trajectories show the anti-clockwise motion of air parcels in the vorticity
center.

The iso-surface of potential vorticity shows that the stratospheric high
potential vorticity intruded into the upper troposphere. When the upper level
high potential vorticity caught up to the low level depression, the rapid
deepening occurred.

A typical "comma-shaped" cloud system was generated by the cyclone. The
trajectories of the air parcel show that the characteristics of the cloud
system are related to the different kind of air motion. The subtropical warm
air was raising fast from the boundary layer to the upper level (12 km), which
caused the formation of the ice cloud and heavy rainfall. Some moist, but
chilly air, east of the cyclone rose to the higher level and turned to the
southwest, which caused the cloud shield's westward extension and formed a
"cloud hook" in the middle troposphere.

A very dry air mass carried by the upper level northwesterly jet stream from
the tropopause (about 10 km height) was sinking to the lower troposphere (about
1-3 km). It caused a clear area to appear behind the cyclone. One branch of the
dry air flow embroiled into the cyclone, and caused the formation of a thin and
curved dry slot near the cyclone center.

A very strong jet stream flowed over the cyclone on the upper level when the
cyclone deepened. The core of the jet stream, with a speed over 60 m/s, shifted
from the back to the front of the trough. An upper vortex was cut off from the
trough, and a considerable ridge developed on the downstream side of the
cyclone at the upper level.