Publications

Garnier, A; Pelon, J; Pascal, N; Vaughan, MA; Dubuisson, P; Yang, P; Mitchell, DL (2021). Version 4 CALIPSO Imaging Infrared Radiometer ice and liquid water cloud microphysical properties - Part II: Results over oceans. ATMOSPHERIC MEASUREMENT TECHNIQUES, 14(5), 3277-3299.

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 (D-e) 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 12.05 mu m) is informed by the scene classification provided in the V4 CALIOP 5 km 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 (beta(eff)12/10 = tau(a),12/tau(a,10)) and 12/08 (beta(eff)12/08 = tau(a),12/tau(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 similar to 0.1). For the month of January 2008, which was chosen to illustrate the results, median ice D-e and ice water path (IWP) are, respectively, 38 mu m and 3 g m(-2) 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 (<210 K) and 60% in the warmest clouds (>230 K). 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 D-e and IWP are 58 mu m and 97 g m(-2) 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 D-e with MODIS visible-3.7 mu m than with MODIS visible-2.1 mu m in the coldest ST clouds and the opposite for opaque clouds. In prevailingly supercooled liquid water clouds with centroid altitudes above 4 km, retrieved median D-e and liquid water path are 13 mu m and 3.4 g m(-2) in ST clouds, with estimated random uncertainties of 45% and 35 %, respectively. In opaque liquid clouds, these values are 18 mu m and 31 g m(-2) at night, with estimated uncertainties of 50 %. IIR D-e in opaque liquid clouds is smaller than MODIS visible-2.1 mu m and visible-3.7 mu m by 8 and 3 mu m, respectively.

DOI:
10.5194/amt-14-3277-2021

ISSN:
1867-1381