Retrieval of Warm Boundary Layer Cloud Properties in Three Dimensions

 

Author

Roger Marchand — University of Washington

Category

Warm Low Clouds and Interactions with Aerosol

Description

Retrievals of cloud optical and microphysical properties for boundary layer clouds, including those widely used by the ARM project, frequently assume that clouds are sufficiently horizontally homogeneous that scattering and absorption (at all wavelengths) can be treated using one dimensional (1D) radiative transfer, and that differences in the field-of-view of different sensors are unimportant. Unfortunately, most boundary layer clouds are far from horizontally homogeneous, and numerous theoretical and observational studies show that the assumption of horizontal homogeneity can lead to significant errors. The three dimensional (3D) structure of clouds likewise causes significant difficulties in the evaluation of cloud retrievals. The introduction of scanning cloud and precipitation radars at the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program sites presents opportunities to move beyond the horizontally homogeneous assumption. In this poster, we present preliminary results for a 3D retrieval of warm-phase (liquid only) boundary layer cloud microphysical properties. The retrieval uses Ka-band and W-band scanning cloud radar reflectivities, as well as satellite visible and shortwave infrared (SWIR) wavelength imagery (that is, calibrated radiances) in order to estimate 3D cloud liquid water content and effective radius. The retrieval is based on an iterative technique that includes full 3D radiative transfer calculations, in order to ensure that retrieved cloud properties are consistent with both radar reflectivity and VIS/SWIR inputs. While efforts are underway to gather observational data suitable to run this retrieval, the results presented here are based only on simulated radar and satellite dataset.