Structure and Interaction in the Subcloud Region of Thunderstorms

Abstract

The subcloud inflow and outflow structures of two multicell thunderstorms were synthesized from data by a variety of observation systems. The systems included digitized radar, instrumented aircraft, radar chaff, rawinsondes and surface data. The thunderstorms occurred on two consecutive days in northeast Colorado. The data were particularly examined for evidence of horizontal accelerations of the inflow air and hence pressure perturbations in the inflow region and were also examined for indications of interactions between the inflow and outflow air. From the horizontal accelerations it was inferred that widespread but weak mesolows (≤1 mb) existed in the inflow region of each storm. Most of the acceleration appeared to have occurred in the region between the aircraft and environmental rawinsonde observations. The thermal structures of the inflow and outflow regions of both storms are presented. The location of the strongest updrafts near cloud base was generally above and to the rear of the ground-level wind-shift line. This position suggested that the updrafts were enhanced by interaction with the cold air outflow. Possible explanations for the decay of the storms are offered.