On the availability of uncoated mineral dust ice nuclei in cold cloud regions

Abstract

The ice nucleation efficiency of mineral dust decreases when it acquires coatings, e.g. through processing in liquid clouds. This study explores the availability of unprocessed mineral dust for interactions with clouds. We performed forward trajectory calculations originating near the surface of the Chinese Taklimakan desert. The initial specific humidity of each trajectory was assumed to be conserved and used to calculate the relative humidities with respect to water and ice, allowing us to estimate the formation of liquid, mixed-phase and ice clouds downstream. Practically none of the simulated air parcels reached conditions suitable for homogeneous nucleation of ice (T ;≤ -40°C) without experiencing water saturation first. Potentially the biggest impact of mineral dust is predicted to be on mixed-phase clouds. Furthermore, most trajectories passed through icesaturated (but water-subsaturated) regions where "warm" (T ≥, -40°C) ice clouds may form prior to mixed-phase clouds. Copyright 2009 by the American Geophysical Union.