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.
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