Impacts of the Automated Volume Scan Evaluation and Termination (AVSET) on the WSR-88D Velocity-Azimuth Display (VAD) Wind Profile (VWP)

Based on a recent field survey of Steadham (2008), 62% of the eighty operational National Weather Service Forecast Office (NWSFO) staff surveyed expressed a strong need for either faster Volume Coverage Patterns (VCPs) or more frequent low elevation scans. With this group of respondents, more frequent low-elevation scans (37%) and faster VCPs (25%) were specified as the most important scanning strategy improvements. Under many meteorological situations, the rapid evolution of significant low-altitude weather events may not be adequately observed given the rigid update cycles for the operational VCPs. If one could dynamically control the number of scanning angles based on the sampled meteorological return, one could achieve faster volume scan updates. This possibility led to the epiphany of the so-called “Automated Volume Scan Evaluation and Termination” (AVSET) function developed by Chrisman of WSR-88D Radar Operations Center. The AVSET function primarily was designed to terminate the current volume scan after the radar scanned all the elevations with significant radar return. The effect resulted in shortening the elapsed time between data collection on low elevation angles during periods when no significant data were available on the higher elevation angles.

Impacts of the AVSET functionality on the WSR-88D Velocity-Azimuth Display (VAD) Wind Profile (VWP) have not been well addressed. Currently, the WSR-88D VAD algorithm collects Doppler velocity data points along a VAD circle at all elevation angles before wind speeds and directions were computed at a specified height for a display on the VWP. The VWP task was modified to dynamically determine the elevation angles and slant ranges needed to achieve the required heights based on the elevations available on previous volume scan. The AVSET-induced winds plotted on the experimental VWP display were compared to those of the current WSR-88D VWP algorithm. Preliminary results show that the AVSET-induced VWP elevation angle/slant range combinations resulted in additional wind data. Comparative results will be present at the conference.

Reference: Steadham, R, 2008: 2008 National Weather Service Field Study. Part 1: Volume Coverage Pattern Usage. Radar Operations Center, Norman, OK, 28 pp. [Available from WSR-88D Radar Operations Center, 120 David L. Boren Blvd. Norman, OK 73072]