Casebook 6 June 2005
From CHILL
CSU-CHILL Casebook: 6 June, 2005
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 Zdr echo area. Virga or rain shafts that descended into the insect layer caused obvious reductions in the Zdr magnitudes. (See VCHILL example below.) Zdr 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 Zdr values decreased from the insect regime to the rain regime (less than ~ +4 dB).