East Asia Coastal Cyclone

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.

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The light blue isosurface is cloud ice and relative vorticity is colored by temperature. Particle trajectories that pass through the storm center are also colored by temperature.