Precipitation Field and Intrastorm Flow of Supercell Convective Storms

摘要

Single-Doppler radar data, when supplemented by surface and upper-air information, provides good estimates of the intrastorm kinematic structure of supercell storms. Spatially derived fields of radial velocity, defined as radial stretching and cross-beam shear, can be used to identify and track major intrastorm kinematic features. These fields can be computed quickly and required neither storm motion information nor a favorable beam-flow alignment. Comparisons between multi-Doppler analyses (and numerical simulation) and the single-Doppler fields show good correlations of the updraft and downdraft zones as well as storm inflow and outflow areas. Changes in surface precipitation rates, from isolated and squall line supercells, are reflected in changes in the intrastorm flow inferred from single-Doppler data. This offers a new technique for single-Doppler radar analyses. In addition, a detailed study of the changes in supercell surface rainfall rates, over a high-resolution raingage network, suggests that a simple linear relationship eixsts between the maximum point rainfall rate and the areal coverage of threshold rates of 25 mm hr-1 and 55 mm hr-1. Point-area statistical models are presented for individual rain cores, the storm rainfall, and for rainfall over a 4000 km2 watershed. This investigation is the first known detailed study of single-Doppler data and surface rainfall observed over a short time interval. Temporal changes in supercell kinematic structure are related to changes in surface rainfall rates. Supercell rainfall in several different environments are presented. The results suggest that changes in surface rainfall rates are related to changes in intrastorm kinematic flow. (Author)