Cloud thermodynamic phase, cirrus cloud optical thickness and effective diameter in the Version 6 Atmospheric Infrared Sounder data release

The development of a new set of cloud products produced in the upcoming Version 6 release of the Atmospheric Infrared Sounder (AIRS) algorithm is described and initial results are presented. The three new cloud retrieval products include (1) cloud thermodynamic phase, (2) cirrus cloud optical thickness, and (3) cirrus cloud effective diameter. The retrieval methodology of the cirrus cloud parameters is based on an optimal estimation approach that uses Level 1B observed radiances and Level 2 cloud clearing-derived atmospheric profiles that define the atmospheric state, surface temperature and emissivity, and cloud top temperature. The Stand Alone AIRS Radiative Transfer Algorithm (SARTA) is coupled to a delta-4-stream (D4S) approximation (SARTA+D4S) to simulate single-layered cloudy spectra. The same ice scattering models used in the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5 release are also used in the SARTA+D4S model. The error characterization and averaging kernels associated with the retrieved fields, and various challenges to operational implementation, will be highlighted. Statistical comparisons are made to pixel-scale collocated Aqua MODIS retrievals, with similarities and differences quantified in the AIRS products that are sorted into distinct cloud regimes.