The day-to-day co-variability between mineral dust and cloud glaciation: A proxy for heterogeneous freezing

Abstract

To estimate the global co-variability between mineral dust aerosol and cloud glaciation, we combined an aerosol model reanalysis with satellite retrievals of cloud thermodynamic phase. We used the CALIPSO-GOCCP product from the A-Train satellite constellation to assess whether clouds are composed of liquid or ice and the MACC reanalysis to estimate the dust mixing ratio in the atmosphere. Night-time retrievals within a temperature range from +3 to -42 ĝ C for the period 2007-2010 were included. The results confirm that the cloud thermodynamic phase is highly dependent on temperature and latitude. However, at middle and high latitudes, at equal temperature and within narrow constraints for humidity and static stability, the average frequency of fully glaciated clouds increases by +5 to +10 % for higher mineral dust mixing ratios. The discrimination between humidity and stability regimes reduced the confounding influence of meteorology on the observed relationship between dust and cloud ice. Furthermore, for days with similar mixing ratios of mineral dust, the cloud ice occurrence frequency in the Northern Hemisphere was found to be higher than in the Southern Hemisphere at -30 ĝ C but lower at -15 ĝ C. This contrast may suggest a difference in the susceptibility of cloud glaciation to the presence of dust. Based on previous studies, the differences at -15 ĝ C could be explained by higher feldspar fractions in the Southern Hemisphere, while the higher freezing efficiency of clay minerals in the Northern Hemisphere may explain the differences at -30 ĝ C.