A 10-year climatology of globally distributed ice cloud properties inferred from the CALIPSO observations

Abstract. The present study analyzes the climatology of spatiotemporal and vertical distribution characteristics of ice clouds, including the ice cloud fraction (ICF), ice water content (IWC), and ice cloud optical depth (ICOD) for three ice cloud categories (sub-visual, thin, and opaque). Newly released level 3 ice cloud data observed from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) instrument is used for the period 2007–2016. The results revealed that the global means of ICF and IWC were found to be ~ 10 % and ~ 0.0017 g/m³, respectively. On the other hand, the latitude-and-altitude mean distributions of ICF and IWC were found unimodal in all the seasons. During summer, the peak in the ice cloud formation occurred over the equatorial region of the northern hemisphere (NH) which extended further to higher altitudes over the NH equator than the southern hemisphere (SH). However, the opposite was observed in the cold season. This is mainly related to the strong convective activities in tropical areas, variation in the distribution of land and ocean between NH and SH, and the seasonal migration of the inter-tropical convergence zone (ITCZ). Furthermore, the ice clouds detected during the nighttime in summer occurred at high frequency over the SH high-latitude regions, owing to the polar stratospheric clouds (PSCs). The occurrence of sub-visual ice clouds (ICOD < 0.01) was infrequent in the tropics and below 5 % in other regions. Whereas, the opaque ice clouds (0.3 ≤ ICOD < 1, ICOD ≥ 1) occurred most frequently in mid-latitude storm-active regions. The relationships between IWC and relative humidity (RH) and temperature (TE) suggest negative and positive correlations during the nighttime, respectively. However, the relationship between ICOD and these meteorological variables depends on the range of ICOD.