Aerosol influence on clouds, precipitation and climate in EC earth

Principal Investigator(s)

Dr. Trude Storelvmo
ETH-Zurich
Universitaetsstrasse 16
ETH-Zentrum, CHN O 11
CH-8092 Zurich, Switzerland

trude.storelvmo@env.ethz.ch

Project description

The Integrated Forecasting System (IFS) from the European Centre for Medium-Range Weather Forecast (ECMWF) is the atmospheric component of EC-earth, a new European earth system model currently under development. The ambitious goal for the EC-earth community, consisting of researchers from approximately 10 European countries, is to develop an earth system model which, in its final state, will constitute a powerful tool to study weather and climate on a range of different timescales, from weeks to centuries.

Aerosols are modulators of Earth’s radiative balance and hydrological cycle, and are therefore key components in a state-of-the-art earth system model. A sophisticated treatment of aerosols, and their effects on clouds and climate in particular, is therefore currently under development within the EC earth community. The introduction of aerosol effects on clouds (so called aerosol indirect effects) in the IFS is mainly taking place at ETH in Zurich.

A prerequisite for model simulations of aerosol effect on clouds and climate is a method to calculate cloud droplet number concentration (CDNC) based on aerosol mass and/or number concentration. A number of such methods are available in the literature, leading to pronounced differences in estimates of aerosol indirect effects. An extensive comparison of such methods has already been carried out within the IFS framework. The comparison was based on monthly mean aerosol fields, and required a series of longer simulations in order for sound conclusions to be made. The computing time required for these simulations were obtained partly from the special project SPCHLAI (administered by ETH-Z) and partly from the special project CHLAPETH (administered by Meteoswiss).

Currently, a scientific paper on the results is being submitted to a peer-reviewed journal.

The next step in the implementation of aerosol indirect effects in the IFS will be to couple the atmospheric chemistry model TM5 to the IFS. This will ensure more realistic aerosol mass and number concentrations, as aerosols will be transported and deposited in response to the state of the IFS, rather than prescribed. Consequently, IFS estimates of aerosol direct and indirect effects on climate will be more realistic. Before an implementation of these effects in EC Earth, the IFS cloud microphysics scheme must also be modified slightly. In a late request for special projects for 2008, computing time for the plans outlined above has been applied for. If granted, we estimate that this work can be finalized by the beginning of 2009.

Our further plans for improving the treatment of aerosols interaction with clouds, precipitation and radiation, and ultimately their effects on weather and climate, are as follows

In the beginning of 2009, a new 4-year project funded by the EU will start. The name of the project is “Comprehensive Modelling of the Earth System for Better Climate Prediction and Projection (COMBINE)”, and EC earth is one out of seven Earth System Models (ESMs) contributing to this project.

ETH-Zurich is heavily involved in Work Package 2 (Work package leader is Prof. Ulrike Lohmann, ETH-Zurich) of this project, which concerns the representation of aerosols, clouds and chemistry in ESMs. ETH-Zurich is responsible for the following deliverables within WP2: 1) The implementation of and first simulations with improved aerosol-cloud interactions in EC earth (After 18 months, i.e. in 2010). 2) Investigations of the importance of chemistry-aerosol-cloud interactions for the radiative forcing and for cloud feedbacks at a time of doubled CO 2 concentrations.

Both tasks are highly dependent on the availability of sufficient amounts of computing time over the time span of the project, and we therefore apply for continued support over the period 2009-2011 for this Special Project.

Additional information

New project for 2009

Would accept support for 1 year only, if necessary.