Emmy Noether Junior Research Group "Cloud-Climate Feedbacks"

Contact: Johannes Quaas

There are four areas of research of the Junior Research Group on the topic of Cloud-Climate Feedbacks:

1. Aerosol-cloud-climate forcings: Anthropogenic aerosol particles may serve as cloud condensation nuclei and thus alter cloud properties and the cloud's influence on radiation. This climate forcing is not well understood. In the Junior Research Group we have used satellite data to quantify the effect of aerosol on clouds and radiation with the help of statistical correlations, the analysis of ship tracks and of the weekly cycle; and to evaluate the representation of aerosol-cloud interactions in the climate model. This resulted in observational evidence for aerosol effects, which, however, were in most cases much smaller than previous studies suggested. This result was also found for the impact of aerosol on the Indian monsoon.
   
   

2. Interpretation of satellite data: Satellite remote sensing attempts to retrieve atmospheric properties from the measured radiation. We examined satellite data for cloud liquid water, cloud height, and winds, and found several issues. These have to be taken into account when applying and interpreting the data.
   
   

3. Cloud-climate feedbacks: We assessed modes of cloud-climate feedbacks for two regions particularly relevant to the Earth's climate. For the Arctic, our data showed that part of the explanation for the minimum sea ice extent in the year 2007 was in the particularly low cloudiness. In the Amazon region, our results suggest that deforestation impacts cloud properties and thus radiation in a way that implies a warming feedback. On the global scale finally we showed the particular relevance of clouds in the lower atmosphere above the tropical oceans for climate sensitivity. The comparison of observations for these clouds with a simulation study implied a large climate sensitivity.
   
   

4. Model evaluation and improvement: Reliable simulations of future climate change are possible only if the representation of clouds in the model is improved. A focus of the research group is on the statistical description of clouds which are not resolved by the model grid (“subgrid-scale variability”). The evaluation of this statistical description with satellite data, ground-based remote sensing and high-resolved model simulations allowed for an improvement of the formulation. Comparisons of simulated clouds with new satellite data further revealed issues with cumulus and cumulonimbus clouds. New approaches for parameterizations, implemented in collaboration with ETH Zurich and the Dutch weather service, helped to improve the agreement of the simulation with observations.

Between September 2006 and March 2011 scientists of the Junior Research Group published 26 scientific articles. In  education, eight internships, four Bachelor's theses, seven diploma theses, seven PhD theses, and one habilitation were carried out.

Besides funding by the German Research Foundation, our work was supported by the European Commission in three projects of the Seventh Framework Programme, and a project in the Marie Curie Programme, by the excellency cluster “CliSAP”, the German Weather Service, and the Max Planck Society. Computing time was provided by the German High Performance Computing Centre for Climate- and Earth System Research.

Alumni of the Emmy Noether Junior Research Group work at renowned scientific institutions in Europe, such as the ECMWF (Reading, UK), the University of Bergen (Norway), LMD/IPSL (Paris, France) and in Germany (German Research Centre for Geosciences Potsdam, German Weather Service, University of Leipzig).

An overview of our research until 2009 can be found in the interim report for the German Resarch Foundation.