Airborne Radar Observations of Precipitation Formation in Convective Clouds over the Southwestern UK: Preliminary Results from the COPE Project

COPE is a UK led field campaign, motivated by the need to improve quantitative precipitation forecasting for convective storms, that will take place in the South-Western peninsula of England during July and August, 2013. This project will take advantage of a network of observational and research radars, supplemented by airborne observations from the BAe-146 and the University of Wyoming King Air research aircraft. Here we will be using observations from the airborne Wyoming Cloud Radar (WCR) along with in situ observations to investigate how the strength of the warm-rain process and the efficiency with which warm-rain is converted to graupel in the Hallet-Mossop temperature range impacts the formation, distribution, and intensity of precipitation.

The WCR is perversely well-suited to documenting the occurrence of warm rain, which strongly attenuates the return signal. Regions with large concentrations of drops between ~ 0.5 and 2 mm diameter are readily apparent due to attenuation of the radar return. Graupel can also lead to strong extinction of the radar return, although not as strong as for liquid drops for comparable LWC/IWC. As scattering dominates extinction from ice, these regions tend to be marked by a distinct multiple scattering ‘tail'.

We expect that conditions sampled during COPE will, in many ways, resemble those observed during the ICE-T field campaign in the Caribbean, albeit with a somewhat weaker warm-rain process as a result of the cooler cloud base temperatures expected over South-Western England. As such, observations from COPE will be used in conjunction with those from ICE-T in order to help understand how the strength of the warm rain process affects the glaciation of cloud.