Casebook 6 June 2005

CSU-CHILL Casebook: 6 June, 2005

$Z_{dr}$ plot of Virga

Surface conditions were warm and dry when high-based showers occurred in the CSU-CHILL radar coverage area during the afternoon hours of 6 June 2005. Insects flying in the boundary layer generated a widespread low reflectivity / highly positive $Z_{dr}$ echo area. Virga or rain shafts that descended into the insect layer caused obvious reductions in the $Z_{dr}$ magnitudes. (See VCHILL example below.) $Z_{dr}$ is a measure of the reflectivity-weighted mean axis ratio of the scatterers. Thus, as the higher reflectivity raindrops became more common in the radar pulse volume, the $Z_{dr}$ values decreased from the insect regime to the rain regime (less than ~ +4 dB).

example in VCHILL

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