Impacts of High Latitude Local and Long-Range Transported Dust on Arctic Mixed-Phase Clouds through Heterogeneous Ice Nucleation

Abstract:

Mixed-phase clouds are widespread and frequently observed over the Arctic, and have important impacts on the surface energy budget and regional climate. Aerosols such as dust can trigger primary ice nucleation in mixed-phase clouds by acting as ice nucleating particles (INPs) and thus alter the cloud phase and cloud radiative forcing. Dust particles are the most abundant and efficient INPs at temperatures colder than -15 C. Over the Arctic regions, dust aerosols can be originated from both remote subtropical deserts and local high latitude sources. Thus far, high latitude dust (HLD) emissions have received little attention or even been ignored in global climate models. Recent estimates suggested that HLD emissions contribute 2-3% of global dust emissions and thus can be crucial to the Arctic mixed-phase clouds.

In this study, we implemented a source-tagging technique for dust aerosols in the Energy Exascale Earth System Model version 1 (E3SMv1) to explicitly investigate the glaciation effect on Arctic mixed-phase clouds by dust aerosols from high latitude (Arctic) sources and five major low latitude sources (North America, North Africa, East Asia, Central Asia, South Asia). We found that E3SMv1 with HLD emissions significantly improves the model agreements with dust and INP observations at surface sites and aircraft campaigns in the Arctic. HLD is the largest among all the tagged sources, contributing more than 35% to dust concentrations below 800 hPa in the Arctic. During the boreal autumn, HLD accounts for 30 to 50% of the dust immersion freezing below 600 hPa. HLD exerts a radiative cooling effect of 0.3 W m^-2 by prompting the glaciation of mixed-phase clouds in the Arctic during the boreal autumn. For the low latitude dust sources, North Africa provides the most dust over the Arctic at 400 to 600 hPa, while dust from East Asia dominants above 400 hPa. The INP and glaciation effects of low latitude dust sources are also quantified.