Direct and semi-direct radiative effects of absorbing aerosols in Europe: Results from a regional model

Abstract

The influence of absorbing aerosol on atmospheric conditions in Europe is simulated for a summer and a winter period with a regional model. Depending on the fraction of elemental carbon the effects of radiation are determined. Absorbing aerosol increases the average solar heating rate for the summer case by 2.5 × 10 -6 -4.4 × 10 -6 K s -1 (20%-46%) within the boundary layer. Due to the heating by absorbing substances an average decrease of the total cloud cover (summer: 1.0%, winter: 0.7%) is found. This semi-direct radiative effect causes mainly positive forcing near the surface and at the top-of-atmosphere (TOA). Significant negative correlations (summer:-0.7, winter:-0.4) between the aerosol optical depth and the direct radiative forcing (DRF) are determined at the surface. At the TOA the DRF pattern is influenced by the surface albedo and the cloud fraction. A general decrease of 2m temperatures is simulated when using absorbing aerosol compared to an aerosol-free troposphere (summer:-0.14 K, winter:-0.10 K) over land surface. Copyright 2012 by the American Geophysical Union.