A Composite Study of Comma Clouds and Their Association with Severe Weather Over the Great Plains.

摘要

Thirty-five comma cloud systems which existed over the Great Plains during the 1980 and 1981 spring seasons (March through June) are analyzed using visible and infrared satellite imagery, rawinsonde data and gridded data sets. Each comma pattern is divided into eleven zones and the soundings from similar zones are then averaged together. Composite kinematic and thermodynamic quantities are examined on isobaric and relative-flow isentropic surfaces. Severe weather is also stratified by zone. Eighty percent of the severe events are found to have occurred in the comma tail (zones C, D and E). A case study of one particular comma cloud system (March 21-22, 1981) is examined separately. This case was characterized by rapid convective cloud growth which developed in situ within the dry intrusion. Development occurred along a dryline where surface convergence was strong and where cold air advection aloft increased the potential instability. Synoptic-scale vertical motions are calculated and found to be upward in the northern portion of the dry intrusion. Comparisons are made to the composite comma cloud. (Author)