Temperature‐Independent Cloud Phase Retrieval From Shortwave‐Infrared Measurement of GCOM‐C/SGLI With Comparison to CALIPSO
Takashi M. Nagao, Kentaroh Suzuki
Abstract
Abstract The shortwave infrared (SWIR) channels commonly accommodated in satellite‐borne passive sensors contain information on cloud thermodynamic phase as well as cloud optical thickness (COT) and cloud effective radius (CER). This study develops algorithms for simultaneous retrieval of COT, CER, and cloud thermodynamic phase to estimate the fractional probability of the cloud phase as an alternative to discrete discrimination into liquid and ice typical of operational cloud retrievals. Two algorithms were developed and applied to the SWIR channels centered at 1.05, 1.63, and 2.21 μm of Second‐generation Global Imager (SGLI). The first algorithm retrieves COT, CER, and ice COT fractions relative to the total COT, which is a continuous quantity representing the partitioning into liquid and ice phases. The second represents the cloud phase partitioning in the form of differences between radiances observed and simulated under the assumptions of either liquid or ice clouds when retrieving COT and CER. The cloud phases from these algorithms agreed quantitatively with each other, and were able to characterize the phase occurrence on a global scale. The two types of cloud phase characterization were further compared against CALIPSO to find that the zonal‐mean occurrences of the cloud phase from the first algorithm were broadly consistent with those from CALIPSO, except for significantly smaller occurrences of supercooled water clouds in SGLI than in CALIPSO over middle‐to‐high latitude oceans. The cloud phase occurrences were also found to systematically vary with CER and cloud‐top temperature on a global scale in a manner significantly different between SGLI and CALIPSO.