Radar and Meso-Scale Analysis of a Cold Front

Abstract

Meso-scale structure of a cold front is analyzed, using the data from radar and surface meteorographs. The principal results obtained from this analysis are as follows:
1. This cold front is accompanied by many line echoes having a definite orientation (ca. 35°-215°).
2. There are many generation areas of echo cell along the surface of cold front, where convective cells are generated successively. The generated cells remove to leeward (NE), increasing gradually. Thus many line echoes are formed, which extend from the cold front toward the definite direction. And so the line echoes become parallel to the vector difference between the moving velocity of cell and that of generation area. As the echo cells move with 600-700 mb wind and the generation areas move with 700-850 mb wind, the line echoes would be also parallel to the vertical wind shear between the two levels.
3. As a result, where the cold front runs from NNE to SSW, the line echo is situated on the warm air side of cold front and constitutes the so-called prefrontal squall line. While where the front runs from ENE to WSW, the line echoes are arranged on the cold air side and compose the mesoscale pattern of precipitation behind the cold front.
4. The mechanism of generation area is not studied in detail, however, a minor cyclone formed on the cold front is accompanied with several generation areas and considered as a large generation area as a whole.
5. In order to discriminate the cold front from prefrontal squall line, the analysis of pseudo-wet-bulb potential temperature is performed.