Multiple size-distributed populations of CCN and IFN in a 2-moment microphysical scheme of the cloud-resolving model MesoNH

This study focuses on the role of 3D fields of polydisperse and multimodal Aerosol Particles (AP) to shape the microstructure of mixed-phase clouds at fine scale. AP are partitioned into Cloud Condensation Nuclei (CCN) and Ice Forming Nuclei (IFN). Once initialized, AP are transported by the resolved flow at cloud scale and by turbulent motion. Then depending on local conditions, AP are activated to form the cloud droplets or they initiate ice particles by heterogeneous nucleation. Below clouds, AP are scavenged by the raindrops.

The novel aspects of the scheme are: 1. A multimodal extension of the Twomey's theory proposed by Cohard et al. (JAS, 1998) to treat the competition between several sources of CCN with different activation properties. 2. An adaptation of the advanced heterogeneous nucleation scheme of Phillips et al. (JAS, 2008) which considers the deposition/condensation freezing properties of size-distributed IFN, and where the effect of immersion freezing of aged coated IFN, serving first as CCN to nucleate droplets, is included. 3. A detailed below-cloud scavenving scheme of AP (Berthet et al., AR, 2009) following Slinn's parameterization.

The implementation of these developments is made in the 2-moment microphysical scheme of Cohard et al. (JAS, 2000) which is extended to the ice phase to treat the case of mixed-phase clouds in the French mesoscale model MesoNH. Then we explore the potential of the AP scheme by looking to the net effect of secondary sources of CCN and IFN that modify the microstructure of preexisting clouds formed on background AP. We illustrate these aspects by simulating the impact of an additional source of CCN in the boundary layer and by studying the complex effect of a midtropospheric plume of dust, here a source of IFN, impinging on a deep convective storm.