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Columns of differential reflectivity, the difference between the horizontal and vertical reflectivity,hereafter Zdr columns, are vertical columns of enhanced Zdr that extend above the environmental 0°Clevel. These are easily identified when observed by polarimetric radars. Physically, these columns consistof rain dominated by large drops that are being lofted above the freezing level and have been recognizedas a proxy for the location of updrafts. Their potential for nowcasting severe weather has been shown inseveral past studies. We have developed an algorithm that identifies and tracks Zdr columns fromvolumetric radar data along with 3D wind fields from MultiDoppler analysis to spatially correlate Zdrcolumns with updrafts. Since Zdr columns are a manifestation of an updraft, different Zdr columnsproperties for example Zdr column maximum height, volume, and area are expected to be related toupdraft intensity levels. In turn intensification of updrafts, as indicated by changes in the Zdr columnsproperties, should be translated in intensification of observed precipitation at the surface. For theestimation of rain rates, we used a radar-based polarimetric approach, which will allow us to monitor thetemporal evolution for a number of identified convective rain cells. These cells will be identified fromsummer events observed by the C-band polarimetric German network. For each cell, the properties of Zdrcolumns are correlated with rain rate values. Similarly, correlations are also calculated for updraftvolumes, updraft intensity, and other updraft properties. For the nowcasting of observed rain rates, anextrapolation algorithm based on spatial and temporal properties of rain was used. Preliminary resultshave shown that higher precipitation rates are generally associated with Zdr columns, and cells without aZdr column produce lower precipitation rates, as expected. Zdr column height and volume show apositive correlation with precipitation intensity at the surface. The time lag between the intensification ofthe Zdr column and associated increase in precipitation at the surface varies significantly between cells,but it is generally short compared to previous studies, varying mostly between 5 to 15 minutes. An earlyidentification of cells associated with ZDR columns could benefit the skill of the nowcasting of localizedrain cells, which often are smoothed during extrapolation. |
