Articles | Volume 11, issue 4
Development and technical paper
16 Apr 2018
Development and technical paper |  | 16 Apr 2018

The impact of precipitation evaporation on the atmospheric aerosol distribution in EC-Earth v3.2.0

Marco de Bruine, Maarten Krol, Twan van Noije, Philippe Le Sager, and Thomas Röckmann

Abstract. The representation of aerosol–cloud interaction in global climate models (GCMs) remains a large source of uncertainty in climate projections. Due to its complexity, precipitation evaporation is either ignored or taken into account in a simplified manner in GCMs. This research explores various ways to treat aerosol resuspension and determines the possible impact of precipitation evaporation and subsequent aerosol resuspension on global aerosol burdens and distribution. The representation of aerosol wet deposition by large-scale precipitation in the EC-Earth model has been improved by utilising additional precipitation-related 3-D fields from the dynamical core, the Integrated Forecasting System (IFS) general circulation model, in the chemistry and aerosol module Tracer Model, version 5 (TM5). A simple approach of scaling aerosol release with evaporated precipitation fraction leads to an increase in the global aerosol burden (+7.8 to +15 % for different aerosol species). However, when taking into account the different sizes and evaporation rate of raindrops following Gong et al. (2006), the release of aerosols is strongly reduced, and the total aerosol burden decreases by −3.0 to −8.5 %. Moreover, inclusion of cloud processing based on observations by Mitra et al. (1992) transforms scavenged small aerosol to coarse particles, which enhances removal by sedimentation and hence leads to a −10 to −11 % lower aerosol burden. Finally, when these two effects are combined, the global aerosol burden decreases by −11 to −19 %. Compared to the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations, aerosol optical depth (AOD) is generally underestimated in most parts of the world in all configurations of the TM5 model and although the representation is now physically more realistic, global AOD shows no large improvements in spatial patterns. Similarly, the agreement of the vertical profile with Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite measurements does not improve significantly. We show, however, that aerosol resuspension has a considerable impact on the modelled aerosol distribution and needs to be taken into account.

Short summary
Precipitation evaporation (PE) and subsequent aerosol resuspension (AR) are currently ignored or implemented only crudely in GCMs. This research introduces PE to Earth system model EC-Earth and explores ways to treat AR and the impact on global aerosol burden. Simple 1:1 scaling of AR with PE leads to an increase (+8 to 15.9 %). Taking into account raindrop size distribution and/or accounting for in-rain aerosol processing decreases aerosol burden -1.5 to 6.2 % and -10 to -11 %, respectively.