MESOVORTEX CIRCULATIONS SEEN BY AIRBORNE DOPPLER RADAR WITHIN A BOW-ECHO MESOSCALE CONVECTIVE SYSTEM

During the spring of 1991, scientists from the National Severe Storms Laboratory conducted a field observational program to obtain a better understanding of the processes responsible for organizing and maintain ing the dynamical and electrical structure of mesoscale convective sys tems (MCSs), as well as mechanisms acting to organize and propagate th e dryline. Extensive use was made of a relatively new observing tool, the airborne Doppler radar installed on one of the NOAA P-3 research a ircraft, to map the precipitation and kinematic structure of large mes oscale convective systems. The radar was operated in an innovative sca nning mode in order to collect pseudo-dual-Doppler wind data from a st raight-line flight path. This scanning method, termed the fore/aft sca nning technique (FAST), effectively maps out the three-dimensional win d field over mesoscale domains (e.g., 80 km x 1 00 km) in approximatel y 1 5 min with horizontal data spacing of 1-2 km. Several MCSs were ob served over central Oldahoma during May and June of 1991, and one such system exhibiting a ''bow-echo'' structure is described. Many observe d features of this MCS correspond to structures seen in nonhydrostatic numerical simulations. These features include a pronounced bulge or'' ''bow'' in the convective line (convex toward the storm's direction o f propagation), a strong descending rear inflow jet whose axis is alig ned with the apex of the bow, and a cyclonic vortex (most pronounced a t heights of 2-3 km) situated in the trailing stratiform region latera l to the axis of strongest rear inflow. Doppler-derived wind analyses reveal the likely role played by the mesoscale circulation in twisting environmental vertical shear and converging ambient vertical vorticit y in maintaining and amplifying the vortex. The relatively detailed ye t horizontally extensive airflow analyses also reveal the utility and advantages of airborne Doppler radar in the study of large convective systems.