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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
 

Lead Supervisor: Michael Herzog, Geography

 

Brief summary: 
The project will investigate the interaction between convective clouds and their impact on the cloud spectrum with the aim to improve the representation of convection in climate models.
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. The key issue in representing convection in global models is that the resolutions of these models are too coarse to represent individual convective clouds. Instead, models rely on physically based parameterization of convection. Improvements in the performance of climate and numerical weather prediction models will crucially depend on the development of better parametrizations for convection. 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 represents and predicts the spectrum of individual clouds that are possible for given atmospheric conditions. Individual clouds are calculated based on a one-dimensional entraining parcel model; the cloud spectrum calculation is based on a predator-prey approach whereby cloud compete for the convective instability available in the environment. The predicted cloud spectrum is the truly novel aspect of CCFM. It determines not only the strength of convection but also its vertical profiles and the amount of precipitation produced. The aim of this project is to characterise the cloud spectrum and its evolution in high-resolution numerical simulations and to validate prediction from CCFM.
What will the student do?: 
The student will analyse existing output from high-resolution simulations of convection for different atmospheric conditions. These simulations have been performed as part of the ParaCon consortium. The student will interact with members of the ParaCon consortium. The simulations have been performed with a spatial resolution of several tens of metres to hundred metres so that the formation of individual clouds is explicitly resolved. Characteristics of individual clouds will be determined. Ideas for the characterisation of all convective clouds that are present in the simulations will developed and tested against predictions from CCFM. At any given point in time, clouds will be at different stages of their cloud lifecycle. The output frequency of the existing simulations is too low to study the cloud lifecycle in detail. Additional simulations with high-frequency output will be performed to investigate the lifecycle of individual clouds in more detail. A particular focus will be on clouds that merge with other clouds during their evolution. Ways to extent CCFM to include cloud merging will be investigated.
References - references should provide further reading about the project: 
Wagner, T.M. and Graf, H.F. (2010). An Ensemble Cumulus Convection Parameterization with Explicit Cloud Treatment. J. Atmos. Sci., 67: 3854-3869.
Kipling, Z., Stier, P., Labbouz, L., and Wagner, T. (2017): Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2, Atmos. Chem. Phys., 17, 327–342, https://doi.org/10.5194/acp-17-327-2017.
Del Genio, A.D (2012). Representing the Sensitivity of Convective Cloud Systems to Tropospheric Humidity in General Circulation Models. Surv Geophys 33, 637–656, https://doi-org.ezp.lib.cam.ac.uk/10.1007/s10712-011-9148-9.
Applying
You can find out about applying for this project on the Department of Geography page.
Dr Michael Herzog
Department of Geography Graduate Administrator