A remote sensing approach to retrieve fair weather cumulus entrainment rates

Description

Cumulus entrainment is an active area of research due to the changes it induces on cloud development, and by extension the radiative and thermodynamic characteristics of the local environment. We are developing an algorithm named Retrieval of Entrainment and Droplet Density In Cumulus (REDDIC) that promises to retrieve the entrainment rate through ground-based remote sensing observations and thus provide insight into the entrainment process without the use of in situ measurements. Due to the inability to determine life cycle stage or cloud geometry from a fixed point on the surface, REDDIC retrieves a bulk characteristic entrainment rate for an afternoon rather than an individual rate for a specific cloud. Time-averaged thermodynamic profiles from instruments based at the Southern Great Plains ARM site are used as inputs into a cloud parcel model that treats entrainment events explicitly. Effective radius and liquid water path are calculated from the model output and compared to a distribution of those parameters measured during the observation period. Through iterative adjustment, the cloud droplet number concentration and entrainment rate are modified until the modeled properties converge to observations. Initial results will be presented.