The Life Cycle and Internal Structure of a Mesoscale Convective Complex

Abstract

This paper describes the life cycle and precipitation structure of a Mesoscale Convective Complex (MCC) that passed through the data-collecting network of the Texas portion of the High Plains Cooperative Program (HIPLEX) on 8 June 1980. The MCC was the third in a sequence of five mesoscale convective systems that formed in association with a low-level frontal zone, short-wave perturbations in the 500 mb flow, outflow from previous convection, and upslope forcing. Quantitative radar data, together with surface, upper-air and satellite data, were used to determine the three-dimensional structure of the MCC. Isolated echoes formed over the Davis Mountains of far western Texas and merged as they moved eastward to form a mesoscale convective system with a lifetime of ?24 h and a low-level precipitation pattern ?500 km across. The leading edge of the low-level precipitation pattern was a north-south line of intense convective cells possessing the echo structure and low-level kinematic and thermodynamic characteristics typical of a squall line. Behind the leading edge was a well-defined minimum of reflectivity in the transition zone where convective cells dissipated. To the rear of the transition zone, an extensive region of precipitation was organized, during the system's mature stage, as a set of curved rainbands. Vertical cross sections through the rainbands show indications of weak cells in an otherwise stratiform radar reflectivity pattern possessing a distinctive radar bright band. A composite wind analysis shows a center of cyclonic inflow at 500 mb near the common center of curvature of the rainbands. The banded structure of precipitation behind the transition zone suggests an interaction between the mesoscale circulation of the MCC and the fine-wale substructure of its precipitation pattern. Anticyclonic outflow at 200 mb, together with inflow new 500 mb, suggests upward motion in the middle- and upper-level clouds in this region. Thermodynamic data behind the transition zone show the characteristic profile associated with a mesoscale unsaturated downdraft below a deep cloud based at middle levels.