P4.2
On the investigation of vertically integrated liquid (VIL) using WSR-88D's new volume coverage patterns
Vincent T. Wood, NOAA/NSSL, Norman, OK; and R. A. Brown and D. R. Cheresnick
Current WSR-88D volume coverage patterns (VCPs) 11 and 21 are compared with new VCPs that are tentatively called VCP Beta, Gamma, and Delta. The new VCPs are designed to improve temporal and vertical sampling of the atmosphere, thus leading to improved warnings and forecasts. VCP Beta consists of 12 unique elevation angles (0.5-8.1 deg) in 5 min and is designed to sample shallow or more distant convection. VCP Gamma (14 unique elevation angles from 0.5-19.5 deg in 4.1 min) is a faster and denser (at lower elevation angles) version of VCP 11 designed to sample deep convection. VCP Delta consists of 6 unique elevation angles from 0.5-6.5 deg in 2.3 min and permits scanning of fast-evolving damaging events such as tornadoes and microbursts. The lower elevation angles in VCPs Beta-Delta are separated by about 0.5 deg, as compared to the conventional 1.0 deg.
In this study, both measured and simulated values of vertically integrated liquid (VIL) are compared using the current and new VCPs. VIL is a measure of the liquid water in a vertical column and is computed as a function of the vertical profile of reflectivity. It is used by National Weather Service forecasters to estimate the severity of thunderstorms.
For a given VCP, simulated VIL values are computed using six different vertical profiles of reflectivity within an individual convective cell. In the case where the storm's core of maximum reflectivity occurs at the surface, the computed VIL value correspond well with the true storm VIL value with increasing range from the radar. Beyond the range where the lowest elevation angle is above the reflectivity maximum, VIL values decrease to zero. In another case where the reflectivity core is maximum at mid-altitudes, the VIL values fluctuate about the true storm VIL value and then slowly increase as the radar beam broadens with increasing range. After the lowest elevation angle is above the height of maximum reflectivity, VIL values rapidly decrease to zero with increasing range. VCP 21 and Delta produce much greater fluctuations with increasing range owing to the large gaps in the volume coverage at the higher elevation angles.
Real VIL comparisons are made using the Oklahoma City WSR-88D KTLX and a testbed WSR-88D in Norman. KTLX provided VIL values using VCPs 11 and 21. The testbed WSR-88D provided VIL values using new VCPs Beta, Gamma, and Delta. In order to eliminate beam sampling differences, comparisons were made only for storms that were located at roughly equal distances from both radars.
Poster Session 4, Radar Applications
Tuesday, 13 August 2002, 3:00 PM-4:30 PM
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