Fine Structure of Gust Fronts Obtained from the Analysis of Single Doppler Radar Data

[摘要] Doppler velocity data obtained from a single Doppler radar are used to examine fine structures of gust fronts associated with severe thunderstorms. Fields of inflection points of velocities (on surfaces scanned by a radar) are analyzed and are compared with the fields of spectrum width of Doppler velocity and horizontal shear. The analysis is performed on the cases of May 9, 1981 and April 13, 1981 in Oklahoma. In the first case, a gust front consisted of an evolving undulate bore with three separate waves or discontinuities. Two of these waves are detected as a 60km stretch of inflection points of Doppler velocity, whereas the third is marginally evident. For both cases, the length representing secondary features behind the main discontinuities are short (less than 20km) and transient. Careful examinations of the structures at low altitude show that large spectrum width and large shear areas exist slightly behind the main line of inflection points. However, there is a multitude of areas with large shear and spectrum width that have no corresponding inflection point lines. Thus, these two parameters, spectrum width and horizontal shear, alone are not suitable for detection of gust fronts. Besides showing the presence of gust fronts, inflection points can also be good indicators of atmospheric waves. We discuss a pattern of such waves that are embedded in the environmental flow ahead of a gust front.

[学科分类] 大气科学