PNNL

Abstract

This paper analyzes the temperature, cloud type and life stage dependencies of phase partitioning in mixed-phase clouds spanning tropics, midlatitudes, and the Arctic, using data from ground-based remote sensing measurements in Alaska and aircraft measurements from three field campaigns. The results show (1) the liquid fraction in Arctic stratiform clouds decreased from 1 to 0.6 between 0?C and -30?C, and was lower in spring because of the higher dust occurrence in Barrow; (2) In wintertime orographic clouds, the liquid fraction was greater than 0.8; (3) Phase partitioning in convective clouds varied significantly with life stages. At developing stage, it decreased from 1 to 0.3 between -5?C and -15?C, indicating rapid ice generation. While at mature and dissipating stages, the liquid fractions were lower; (4) The stratiform regions of mesoscale convective systems were dominated by ice, with liquid fractions lower than 0.2; (5) The variability of phase partitioning varied for different cloud types. In stratiform clouds, liquid dominated at warm temperatures. As the temperature decreased, ice-dominated region was more frequently observed, while the occurrence of mixed-phase region remained low; For convective clouds, the variability of phase partitioning was controlled by continuous glaciation with decreasing temperature and life cycle.