Global and regional patterns in high ice water content conditions

Conditions of high ice water content (HIWC; defined herein as at least 1.0 g m(-3)) are often found in the anvils of convective systems and can cause engine damage and/or failure in aircraft. We use ice water content (IWC) retrievals from satellite-borne radar and lidar (CloudSat and CALIOP) to provide the first analysis of global HIWC frequency using 11 years of data (2007-17). Results show that HIWC is generally present in 1%-2% of CloudSat and CALIOP IWC retrievals between flight level 270 (FL270; 27 000 ft or 8.230 km) and FL420 (42 000 ft or 12.801 km) in areas with frequent convection. Similar rates of HIWC are found over midlatitude oceans at relatively low altitudes (below FL270). Possible nonconvective mechanisms for the formation of this low-level HIWC are discussed, as are the uncertainties suggesting that the results at these low altitudes are an overestimation of the true threat of HIWC to aircraft engines. The satellite IWC retrievals are also used to validate an HIWC diagnostic tool that provides storm-scale statistics on HIWC over the contiguous United States (CONUS) during the summer convective season (May-August from 2012 to 2019). Results over the CONUS suggest that HIWC over the Great Plains is highest in June, when a point in the region is under HIWC conditions for approximately 25 h of 30 days on average. The mean area-equivalent diameters of HIWC conditions in some areas of the Great Plains exceed 350 km, and the conditions can persist for 4-5 h.