An aerosol-climate model evaluation study in the framework of the (AC)^3 project

In the Arctic, climate warming is about twice as fast as the rest of the world. However, various feedback mechanisms that potentially play an important role are yet poorly understood. The German project “Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms” (AC)³is dedicated to better quantify relevant processes and broaden the understanding of the mechanism involved with a range of field measurements and modelling. Aerosol plays an important role by modulating the Arctic energy balance. This study contributes to (AC)³by exploring sources and transport pathways of aerosol as well as their impact on radiation by atmospheric modelling. When looking at the direct radiative forcing, black carbon (BC) is of particular importance. BC is highly absorbing in the solar spectrum and tends to warm the atmosphere. When deposited on snow/ice it lowers the surface albedo and accelerates sea ice melting. Here, we test the capability of the aerosol-climate model ECHAM6.3-HAM2.3 to reproduce observed BC concentrations using different combinations of emission datasets (ACCMIP, ACCMIP + GFAS and ECLIPSE + GFAS). The runs were performed in nudged mode at T63 resolution (approximately 1.8°) with 47 levels for the years 2006-2015. The model results are compared among each other and evaluated against ground-based in-situ and remote sensing, as well as airborne measurements. The following questions are addressed in the evaluation: 1) Are the sources and transport pathways of aerosol to the Arctic region captured? 2) Is the annual cycle of aerosol conditions represented throughout the altitude levels? 3) How well are specific biomass burning events captured? After thorough evaluation, the model results will provide a state-of-the-art estimate of the budget and radiative forcing of anthropogenic aerosol in the Arctic region.