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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Michael Herzog, Geography 

Importance of the area of research concerned: 
The amount of convective precipitation, for example in thunderstorms, dominates atmospheric heating in the tropics and is a main driver for large scale dynamics. Cloud microphysical processes in convective clouds are only very crudely represented in today’s state-of-the-art climate models. To represent the effect of convective clouds parameterisations are used that typically only describe the integral effect of many clouds. Details of the cloud and precipitation formation are not represented. Aerosol particles that are needed for the cloud formation are ignored completely although a strong influence on convection has been suggested (Rosenfeld et al., 2008) . Large biases exist between observed and simulated amount of tropical precipitation. This uncertainty also dominates the spread in estimates of climate sensitivity, the expected warming due to CO2 doubling. This project seeks to improve the representation of convective precipitation in climate models. The project will contribute to the joint NERC and Met Office programme ParaCon (Parametrization of Convection). The aim of ParaCon is to significantly improve the representation of convection across model scales from 1-100km.
Project summary : 
The project will be based on the Convective Cloud Field Model (CCFM, described in Wagner and Graf, 2010). CCFM is new type of parameterization for convection that explicitly respresents individual clouds using a one-dimensional entraining parcel model. Initial tests of CCFM have been performed within the ECHAM climate model. An improved cloud microphysics that includes interactions with aerosol particles will be added to this entraining parcel model. The effect of aerosol particles on convection will be tested, first within CCFM in stand-alone mode, later within the ECHAM climate model in single column and global configurations . The impact on the simulated climate will be investigated.
What will the student do?: 
The new aerosol-cloud microphysical module will combine a treatment of aerosols acting as cloud condensation and ice nuclei with a synthesis of several existing cloud-microphysical schemes that predict mass and number of various hydrometeor classes. The main focus of this development will be the accurate treatment of the interaction between competing processes over time. Work will be performed within the framework of the entraining parcel model used within CCFM. The student will interact with members of the ParaCon consortium. Dynamical aspects of CCFM are currently been developed and tested as part of ParaCon. Improvements in the representation of cloud and precipitation formation from the project will be an important contribution to ParaCon.
Wagner, T.M. and Graf, H.F. (2010). An Ensemble Cumulus Convection Parameterization with Explicit Cloud Treatment. J. Atmos. Sci., 67: 3854-3869.
Rosenfeld, D., U. Lohmann, G.B. Raga, C.D. O’Dowd, M. Kulmala, S. Fussi, An. Reissell, M.O. Andreae (2008). Flood or drought: How do aerosols affect precipitation? Science, 321: 1309-1313.
You can find out about applying for this project on the Department of Geography page.