Observational estimates of entrainment rate in convective clouds

English Abstract:

The mixing of environmental air across the cloud interface plays a significant role in the lifecycle of the convective cloud system and subsequent influences on the hydrological and energy cycles. Despite its importance, the entrainment process remains poorly understood and its measurement and its quantification is extremely difficult. We present a remote sensing technique that builds upon previous aircraft in-situ based techniques (Lu et al. 2012) in order to estimate the vertical profile of entrainment rate. The profile of vertical velocity observed by the Ka-band ARM Zenith Radar (KAZR) is used with an adiabatic parcel model that incorporates conservation of total water and energy in the retrieval algorithm. This initial study concentrates on five years of non-precipitating cumulus observations over the ARM SGP site, where radar-based observations of mean Doppler velocity are a reasonable proxy for the in-cloud air motion. A preliminary application of the methodology has shown reasonable agreement with simple bulk entrainment estimates using an entraining plume model (Jensen et al. 2006).