#A06 Light-absorbing particles in snow and ice

Abstract

Light-absorbing particles (LAPs) such as black carbon (BC) and dust in snowpack and sea ice can reduce the surface albedo and increase the speed of snow/ice melting, leading to a surface warming in the Arctic as well as lower latitudes across the northern hemisphere. To improve the compatibility between the treatment of atmospheric aerosols and the treatment of LAPs in snow over land and snow/ice over ocean, the ACME model has been modified to separately treat BC mixed internally within hydrometeors and externally with hydrometeors and to use size-dependent BC optical properties (i.e., depending on snow grain size and BC particle size). These modifications along with changes to the atmospheric aerosol transport and deposition have a substantial influence on the concentration and radiative impact of LAPs in snow/ice. Here we use one-year nudged low-resolution (ne30) F-2000 simulations to quantify the deposition rate and concentrations of LAPs and their radiative impact in ACME. Under the present-day conditions, LAPs in snow/ice have an annual mean positive clear-sky radiative forcing of up to 20 W m^-2 over areas covered by snow/ice. There is a strong seasonal cycle in the forcing magnitude determined by changes in insolation and snow/ice cover. Under the all-sky conditions, the LAPs-induced radiative forcing ranges from 2 to 10 W m^-2 in the boreal spring and summer over the Arctic, having great implications for the role of LAPs in melting snow/ice and warming the Arctic. We will discuss these results as well as further model developments needed for a more accurate/comprehensive representation of LAPs in snow/ice.