How Complete Is Cloud Glaciation?

Abstract Below 0C, cloud droplets can freeze, altering a cloud's optical and radiative properties and thereby affecting Earth's energy balance. The microphysical mechanisms that govern this process, known as glaciation, are expected to act on minute timescales. Nevertheless, stratiform clouds can persist in the mixed‐phase temperature range (from 0C to −38C) for hours, thus glaciation events remain poorly characterized. Here, we analyze satellite observations of individual cloud tops to track their temporal phase evolution and to quantify the extent of glaciation. We find that most glaciation events do not result in complete freezing; rather, they induce a sustained shift in cloud properties while the clouds remain in the mixed‐phase regime. Our results indicate that higher hemispheric and seasonal concentrations of ice‐nucleating particles correlate with glaciation occurrence rate. Future studies can utilize our phase‐evolution and glaciation data sets to evaluate how well weather and climate models simulate mixed‐phased cloud evolution and phase heterogeneity.