Detailed flow, hydrometeor and lightning characteristics of an isolated, hail producing thunderstorm during COPS

Kurzfassung

A detailed analysis of air flow, hydrometeor characteristics, cloud-top height, and lightning is presented for the 15/07/2007 case during the Convection and Orographically Induced Precipitation Study (COPS) field campaign. In a synergetic manner, the study makes use of multiple-Doppler analysis from three operational radars, POLDIRAD's polarimetric capabilities, data from different channels of Meteosat Second Generation (MSG) satellite, as well as lightning data to document the life cycle of deep convection. The cloud-top height derived from MSG infrared channel and radar volume scans increased rapidly during 14:20 and 14:35 UTC. The most active phase was identified during 14:35 and 14:45 UTC when cloud tops reached the tropopause, lightning occured with a maximum rate of 15 strokes per minute, and hail was detected via polarimetric radar products. During the cell's lifetime horizontal and vertical flow were derived from four consistent triple-Doppler calculations with 500 m and 15 min space and time resolution, respectively. A main updraft was identified to originate from the more humid air masses to the east of the convergennce line responsible for the cell initiation. Consistency checks of the calculated wind fields with the observed radial velocities were performed. Areas of enhanced discrepancies between the observing systems (during the early phase of mature state) match with areas of higher turbulence marked by polarimetric radar parameters. Moreover, lightning locations correspond well with volumes of distinct vertical motion, particularly within regions of extended updrafts. By interpreting hydrometeor types from polarimetric radar data the evolution of the fraction of different types per volume is investigated. While during the early phase of thunderstorm the fraction of ice (snow, graupel, hail) in the upper cloud part became enhanced, the fraction of rain increased during the decay phase.