Datensatz

Zusammenfassung

The secondary ice process (SIP) in cumulus clouds is a major microphysical process, which can result in rapid enhancement of ice particle concentration in the presence of pre-existing ice. We present results of airborne investigations of Cumulus Congestus clouds (CuCg) from seven field campaigns spanning the time period from 2011 – 2022: ICE-T, SEAC⁴RS, UAEREP (2), CAMP²Ex, SPICULE and ESCAPE. The SPEC Learjet research aircraft participated in all of the field projects accompanied by other research aircraft in five of the seven projects. The results presented are a synthesis of measurements of marine and continental CuCg from the Caribbean, Southeast U.S., South China Sea, UAE and U.S. High Plains. The composite data indicate that after the first primary ice typically formed at temperatures colder than about -8°C, subsequent production of ice via the fractured frozen drop (FFD) SIP was strongly related to the concentration of supercooled large drops (SLDs), with diameters from about 0.2 mm to a few mm. The concentration of SLDs is directly linked to the rate of collision-coalescence, which in turn depends primarily on the subcloud aerosol size distribution and cloud base temperature. Once the production of small ice is initiated via the FFD SIP, the differential in fall velocities between small ice and SLDs creates an avalanche process that rapidly freezes the supercooled region of an updraft core. Other SIP mechanisms, Hallett-Mossop and ice-ice collisions, are also considered. These studies provide the framework for a consistent picture of FFD SIP parameterization in weather prediction models.