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, an aerosol model reanalysis was combined with satellite retrievals of cloud thermodynamic phase. We used the CALIPSO-GOCCP and DARDAR products from the A-Train satellite constellation to obtain the cloud phase and the MACC reanalysis to estimate the dust mixing-ratio in the atmosphere. Night-time retrievals within a temperature range from +3 °C to −42 °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 mid- and high latitudes, at equal temperature and within narrow constrains for humidity and static stability the average frequency of fully glaciated clouds increase by +5 to +10 % for higher mineral dust mixing-ratios. The differentiation between humidity-stability regimes reduced the confounding influence of meteorology on the observed relationship between dust and cloud ice. Furthermore, for 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 °C but lower at −15 °C. This may suggest a difference in the susceptibility of cloud glaciation to the presence of dust. Based on previous studies, the differences at −15 °C could be explained by higher feldspar fractions in the Southern Hemisphere, while the differences at −30 °C may be explained by the higher freezing efficiency of clay minerals in the Northern Hemisphere.