A microphysical retrieval scheme for continental low-level stratiform clouds: Impacts of the subadiabatic character on microphysical properties and radiation budgets

Using measurements from the Department of Energy's Atmospheric Radiation Me asurement Program, a modified ground-based remote sensing technique is deve loped and evaluated to study the impacts of the subadiabatic character of c ontinental low-level stratiform clouds on microphysical properties and radi ation budgets. Airborne measurements and millimeter-wavelength cloud radar data are used to validate retrieved microphysical properties of three strat us cloud systems occurring in the April 1994 and 1997 intensive observation periods at the Southern Great Plains site. The addition of the observed cloud-top height into the Han and Westwater re trieval scheme eliminates the need to invoke the adiabatic assumption. Thus , the retrieved liquid water content (LWC) profile is represented as the pr oduct of an adiabatic LWC profile and a weighting function. Based on in sit u measurements, two types of weighting functions are considered in this stu dy: one is associated with a subadiabatic condition involving cloud-top ent rainment mixing alone (type I) and the other accounts for both cloud-top en trainment mixing and drizzle effects (type II). The adiabatic cloud depth r atio (ACDR), defined as the ratio of the actual cloud depth to the one deri ved from the adiabatic assumption, is found to be a useful parameter for cl assifying the subadiabatic character of low-level stratiform clouds. The ty pe I weighting function only exists in the lower ACDR regime, while the typ e II profile can appear for any adiabatic cloud depth ratio. Results indicate that the subadiabatic character of low-level stratiform cl ouds has substantial impacts on radiative energy budgets, especially those in the shortwave, via the retrieved LWC distribution and its related effect ive radius profile of liquid water Results also show that this subadiabatic character can act to stabilize the cloud deck by reducing the in-cloud rad iative heating/cooling contrast. As a whole, these impacts strengthen as th e subadiabatic character of low-level stratiform clouds increases.