Retrieval of ice cloud microphysics by synergy use of CloudSat and CALIPSO data

We examined the global distribution of ice cloud microphysics from CloudSat and CALIPSO in October 2006. We first developed the synergy cloud mask scheme to specify cloud pixels. Radar-only mask was the same as in 2B- GEOPROF for CloudSat but the lidar mask was developed and was different from the CALIPSO Vertical Feature Mask (VFM) in order to remove the contamination of aerosol signals and noise signals into clouds. Radar-lidar algorithm was modified from the algorithm described in [I]. The applicability of the radar-lidar algorithm was limited to the relatively thin cloud portions where both the radar and the lidar could detect the signals due to clouds. In addition to such limitation, it turned out that there were some portions where the retrievals of ice cloud microphysics were not possible because lidar backscattering coefficient was too high with respect to the radar reflectivity factor and we could not find the solutions of microphysics of ice clouds. The specular reflection phenomena were found in these regions. These indicated the existence of horizontally oriented ice particles. In order to overcome the problem, the treatment of specular reflection was introduced in the new radar-lidar algorithm. The modified algorithm used depolarization ratio at 532nm in addition to backscattering coefficient from CALIPSO and radar reflectivity factor from CloudSat. The new algorithm allowed co- existence of horizontally oriented particles and randomly oriented crystals and retrieve the mixing ratio of oriented crystals. The effect of the modification was significant, i.e., the whole portion of cloud detected by radar and lidar could be retrieved by the new algorithm. Global distribution of ice microphysics in October 2006 was studied. Latitude-height distribution of effective radius indicated that 40 nm-particles were dominated above 13km, 10km and 7km in the tropics, mid-latitude and polar region. And the effective radius and IWC decreased as altitude of clouds decreased. In the lower altitude region, large horizontally oriented particles were found with relatively higher concentration.