The project is structured into 4 tasks that all involve at least two partners.
Task 1 is dedicated to the project coordination, dissemination of the results and valorization.
Task 2 focuses on the development and application of an automatic tuning strategy at the process level. It aims at objectively determining the values of the different free parameters that arise in the different parameterizations involved in the representation of boundary-layer clouds. This will be applied to the comparison of Single Column Model runs to Large-Eddy Simulations (high-resolution simulations). Beyond the determination of the parameter values, this tool will provide a more comprehensive documentation of the parametrization behaviour and we hope through this project to demonstrate that such tools are crucial for parametrization development.
Task 3 is dedicated to the quantification of the cloud radiative effects. Its main realisation will consist in applying to LES results a state-of-the-art radiative code based on 3D Monte-Carlo algorithm. In addition to radiative computations, this code has the capability to compute the sensitivity of outputs to input parameters. This will provide references for the evaluation and tuning of SCM versus LES results. Besides, this Monte-Carlo code will be used to explore the various hypotheses made in the radiative computation in global models (cloud overlap, subgrid-scale inhomogeneities ...).
Task 4 will propose and test new developments in the boundary-layer cloudparameterizations s addressing boundary-layer dynamics, cloud characteristics and cloud radiative effects . This task strongly relies on the two previous tasks. The automatic tuning will provide the range of acceptable values for the free parameters, and identify the most uncertain parameters. A more comprehensive understanding of the parametrization behaviour will also be achieved and will stimulate new developments. We will also revisit the parametrizations themselves, assessing the added value of : (i) representating dry air intrusion, key element in the transport of water vapour, (ii) better representating subgrid horizontal and vertical heterogeneities of clouds, the overlap assumption for cloudy grids as well as the importance of the solar zenithal angle. The improved and tuned parametrizations will be tested systematically in full 3D configuration with the IPSL and CNRM climate and weather forcecast models and compared with satellite and in-situ observations both on a day-by-day basis in a nudged or forecast mode or statistically in climate simulations.
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