Version 4 CALIPSO Imaging Infrared Radiometer ice and liquid water cloud microphysical properties - Part II: Results over oceans
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Abstract. Following the release of the version 4 Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data products from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission, a new version 4 (V4) of the CALIPSO Imaging Infrared Radiometer (IIR) Level 2 data products has been developed. The IIR Level 2 data products include cloud effective emissivities and cloud microphysical properties such as effective diameter (De) and water path estimates for ice and liquid clouds. This paper (Part II) shows retrievals over ocean and describes the improvements made with respect to version 3 (V3) as a result of the significant changes implemented in the V4 algorithms, which are presented in a companion paper (Part I). The analysis of the three-channel IIR observations (08.65, 10.6, and 12.05m) is informed by the scene classification provided in the V4 CALIOP 5km cloud layer and aerosol layer products. Thanks to the reduction of inter-channel effective emissivity biases in semi-transparent (ST) clouds when the oceanic background radiance is derived from model computations, the number of unbiased emissivity retrievals is increased by a factor of 3 in V4. In V3, these biases caused inconsistencies between the effective diameters retrieved from the 12/10 (eff12/10=a,12/a,10) and 12/08 (eff12/08=a,12/a,08) pairs of channels at emissivities smaller than 0.5. In V4, microphysical retrievals in ST ice clouds are possible in more than 80% of the pixels down to effective emissivities of 0.05 (or visible optical depth 0.1). For the month of January2008, which was chosen to illustrate the results, median ice De and ice water path (IWP) are, respectively, 38m and 3gm2 in ST clouds, with random uncertainty estimates of 50%. The relationship between the V4 IIR 12/10 and 12/08 microphysical indices is in better agreement with the severely roughened single column ice habit model than with the severely roughened eight-element aggregate model for 80% of the pixels in the coldest clouds (<210K) and 60% in the warmest clouds (>230K). Retrievals in opaque ice clouds are improved in V4, especially at night and for 12/10 pair of channels, due to corrections of the V3 radiative temperature estimates derived from CALIOP geometric altitudes. Median ice De and IWP are 58m and 97gm2 at night in opaque clouds, with again random uncertainty estimates of 50%. Comparisons of ice retrievals with Moderate Resolution Imaging Spectroradiometer (MODIS)/Aqua in the tropics show a better agreement of IIR De with MODIS visible3.7m than with MODIS visible2.1m in the coldest ST clouds and the opposite for opaque clouds. In prevailingly supercooled liquid water clouds with centroid altitudes above 4km, retrieved median De and liquid water path are 13m and 3.4gm2 in ST clouds, with estimated random uncertainties of 45% and 35%, respectively. In opaque liquid clouds, these values are 18m and 31gm2 at night, with estimated uncertainties of 50%. IIR De in opaque liquid clouds is smaller than MODIS visible2.1m and visible3.7m by 8 and 3m, respectively.
