Master thesis: Modeling aerosol/cloud interaction in the context of Large Eddy Simulation

Contact: Annica Ekman (IAC), Julien Savre

Background: Large Eddy Simulation (LES) constitutes a powerful numerical tool to better understand the physics of small scale cloud processes (a few kilometers in extent) such as entrainment above stratiform cloud layers, the influence of updrafts and downdrafts in cloud dynamics or the interactions between liquid/ice microphysics and dynamics. A new LES model is currently developed at the Department of Meteorology, Stockholm University. The numerical code is based on the MIT Cloud Resolving Model (MIT-CRM, Wang and Chang, 1993) and the model solves the balance equations for three wind components, ice/liquid potential temperature and water vapor mass mixing ratio. The physical properties of five different types of hydrometeors (cloud droplets, rain drops, ice crystals, graupel and snow) are represented using a two-moment bulk microphysics model (i.e. mass and number of the hydrometeors are predicted). The original MIT-CRM includes a comprehensive aerosol/chemistry module which allows for detailed investigation of aerosol-cloud interactions. This feature formed an important aspect of the original model given the known impact of aerosols on the atmospheric radiative budget through direct and indirect (via their interactions with clouds) effects. However, during the development of the LES code, the explicit aerosol module was at first omitted for simplification purposes.

Objective: The main aim of this project is to implement an explicit aerosol module (based on the previous MIT-CRM version) into the LES code and to evaluate the performance of the LES model - with and without the new aerosol component.

Requirements: The candidate must possess good programming skills in Fortran 90 and a willingness to contribute to the development of a large numerical code. The candidate must also have a good general knowledge of cloud and aerosol microphysics.

References:

C. Wang and J.S. Chang. A three dimensional numerical model of cloud dynamics, microphysics and chemistry 1. Concepts and formulation. J. of Geophys. Res., 98, 1993