PNNL

Abstract

The surface inferred cloud optical properties from a multifilter rotating shadowband radiometer have been validated against the in situ measurements during the second ARM Enhanced Shortwave Experiment (ARESE II) field campaign at the ARM South Great Plains (SGP) site. On the basis of eight effective radius profiles measured by the in situ Forward Spectra Scattering Probe (FSSP), our retrieved cloud effective radii for single-layer warm water clouds agree well with in situ measurements, within 5.5%. The sensitivity study also illustrates that for this case a 13% uncertainty in observed liquid water path (LWP, 20 g/m2) results in 1.5% difference in retrieved cloud optical depth and 12.7% difference in referred cloud effective radius, on average. The uncertainty of the LWP measured by the microwave radiometer (MWR) is the major contributor to the uncertainty of retrieved cloud effective radius. Further, we conclude that the uncertainty of our inferred cloud optical properties is better than 5% for warm water clouds based on a surface closure study, in which cloud optical properties inferred from narrowband irradiances are applied to a shortwave model and the modeled broadband fluxes are compared to a surface pyranometer.