Using ARM data to evaluate and improve multilayer cloud properties retrieved from the GOES-East data

Description

Current satellite cloud retrieval methods applied to the Geostationary Operational Environmental Satellite (GOES) imager data often adopt single-layered cloud assumptions, while day-to-day observations of cloud vertical profiles like those from the Atmospheric Radiation Measurement (ARM) Climate Research Facility exhibit frequent occurrence of multilayer clouds. It has been a challenge using traditional GOES imagery data to retrieve multilayered cloud properties. Here we present a feasible method for the retrieval of multilayered cloud properties using a new suite of multispectral observations onboard the designated GOES-East imager located at 75°W, which provides a basic element of continued cloud observations over the United States. The designated GOES-East imager, started with GOES-12 and replaced by GOES-13 on April 14, 2010, carries five spectral channels at nominally 0.6, 3.9, 6.5, 10.7, and 13.3 μm. The new added 13.3-µm CO2 absorption channel, mainly different from the 12-μm channel of the current GOES-West imager, allows for an improved retrieval of upper-troposphere cloud-top height using a modified CO2-absorption technique developed by Chang et al. (2010). Accurate retrieval of the uppermost cloud top height is fundamental and critical in the feasible method for retrieving multilayer cloud properties. An iterative retrieval procedure invoked ice-overlap-water, two-cloud-layered radiative transfer modeling, similar to the scheme of Chang and Li (2005), which is then used to determine a multilayered cloud mask from the GOES data. The method retrieves separately upper- and lower-layer cloud properties when a multilayered cloud pixel is determined. In this study, the ARM Active Remotely Sensed Cloud Locations (ARSCL) data taken at the Southern Great Plains (SGP) site are used to evaluate the multilayered clouds retrieved from the GOES-East data. Comparisons with the ARSCL data show that the GOES-retrieved upper-layer cloud top heights are generally lower, whereas lower-layer cloud top heights generally higher. The biases and improvements in the GOES-retrieved multilayered cloud properties are presented and discussed.