Cloud Top Phase Characterization of Extratropical Cyclones over the Northeast and Midwest United States: results from IMPACTS

Cloud top phase (CTP) impacts cloud albedo and pathways for ice particle nucleation, growth, and fallout within extratropical cyclones. This study uses airborne lidar, radar, and RAP initialization data to characterize CTP within extratropical cyclones as a function of cloud top temperature (CTT). During the 2020, 2022, and 2023 Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign deployments, the Earth-Resources 2 (ER-2) aircraft flew 26 research flights over the Northeast and Midwest U.S. to sample the cloud tops of a variety of extratropical cyclones. A training dataset was developed to create probabilistic phase classifications based on Cloud Physics Lidar measurements of known ice and liquid clouds. These classifications were then used to quantify dominant CTP in the top 150 m. Case studies are presented illustrating examples of supercooled liquid water at cloud top at different CTT ranges (‑3°C<CTTs<-35°C) within extratropical cyclones. During IMPACTS, 19.2% of clouds had supercooled liquid water present. Supercooled liquid was the dominant phase in extratropical cyclone cloud tops when CTTs were > -20°C. Liquid-bearing cloud tops were also found at CTTs as cold as -37ºC. Cloud top heights, CTTs, and CTP showed no dependence on storm type sampled during IMPACTS.