Fast simulators for satellite cloud optical centroid pressure retrievals; evaluation of OMI cloud retrievals

摘要

The cloud Optical Centroid Pressure (OCP) is a satellite-derivedparameter that is commonly used in trace-gas retrievals toaccount for the effects of clouds on near-infrared throughultraviolet radiance measurements. Fast simulators are desirableto further expand the use of cloud OCP retrievals into theoperational and climate communities for applications such asdata assimilation and evaluation of cloud vertical structure ingeneral circulation models. In this paper, we develop andvalidate fast simulators that provide estimates of the cloudOCP given a vertical profile of optical extinction. We use apressure-weighting scheme where the weights depend upon opticalparameters of clouds and/or aerosols. A cloud weighting functionis easily extracted using this formulation. We then use fastsimulators to compare two different satellite cloud OCPretrievals, from the Ozone Monitoring Instrument (OMI), withestimates based on collocated cloud extinction profiles from acombination of CloudSat radar and MODIS visible radiance data.These comparisons are made over a wide range of conditions toprovide a comprehensive validation of the OMI cloud OCPretrievals. We find generally good agreement between OMI cloudOCPs and those predicted by CloudSat. However, the OMI cloudOCPs from the two independent algorithms agree better with eachother than either does with the estimates from CloudSat/MODIS.Differences between OMI cloud OCPs and those based onCloudSat/MODIS may result from undetected snow/ice at thesurface, cloud 3-D effects, cases of low clouds obscurred by ground-clutterin CloudSat observations and by opaque high clouds in CALIPSO lidarobservations, and the fact that CloudSat/CALIPSO onlyobserves a relatively small fraction of an OMI field-of-view.