Retrieval of cloud microphysical properties from the new shortwave array spectroradiometer



Cloud Properties


Connor J. Flynn — University of Oklahoma School of Meteorology
Dan Lubin — Scripps Institution of Oceanography
Andrew M. Vogelmann — Brookhaven National Laboratory


We are developing a radiative transfer retrieval algorithm for use with the new shortwave array spectroradiometer (SAS) data. This will provide high-time-resolution retrievals of cloud thermodynamic phase and optical depth and, for single-phase clouds, liquid water droplet effective radius or ice water effective particle size. The SAS instruments operate over a wavelength range that is very sensitive to cloud properties. Here we concentrate on cloud property retrievals from the SASHE (shortwave array spectroradiometer–hemispheric) instrument, which measures the direct-beam and diffuse hemispheric irradiance spectra in 30-second intervals from about 340–1700 nm. We have analyzed a sample of spectra under overcast skies from the Southern Great Plains site, comprising mainly liquid water but for a variety of optical depths, and have elucidated retrieval confidence and uncertainties. Cloud phase is ascertained by first retrieving the effective cloud optical depth using measurements in the interval 1000–1100 nm and then examining the shape of the spectral irradiance distribution in the 1.6-micron window, which is sensitive to liquid water versus ice and mixed phase. Once a liquid water case has been identified, we then perform a least-squares fit to the irradiances at 1534 and 1593 nm, which have a strong dependence on effective droplet radius. Once this retrieval method is fully developed, it should be a promising asset for diagnosing aerosol indirect effects in cloudy atmospheres.