Microphysical modelling of aerosol scavenging by different types of clouds: description and validation of the approach

Abstract

With dry deposition and below-cloud scavenging, in-cloud scavenging is one of the three components of aerosol transfer from the atmosphere to the ground. There is no experimental validation of in-cloud particle scavenging models for all cloud types that is not impacted by uncertainties concerning below-cloud scavenging. In this article, the choice was made to start with a recognised and validated microphysical cloud formation model (the DEtailed SCAvenging Model, DESCAM) to extract a scheme of aerosol scavenging by clouds, valid for different cloud types. The resulting model works for the two most extreme precipitation clouds: from cumulonimbus to stratus. It is based on data accessible a priori from numerical weather prediction (NWP) outputs, i.e. the intensity of the rain and the relative humidity in the cloud. The diagnostic of the altitude of the cloud base proves to be a key parameter, and accuracy in this regard is vital. This new in-cloud scavenging scheme is intended for use in long-distance (> 100 km) atmospheric transport models (ATMs) or global climate models (GCMs).