Internal variability in a regional climate model over West Africa |
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Authors: | Emilie Vanvyve Nicholas Hall Christophe Messager Stéphanie Leroux Jean-Pascal van Ypersele |
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Institution: | 1. Institut d’astronomie et de géophysique Georges Lema?tre, Université catholique de Louvain, 2 Chemin du Cyclotron, 1348, Louvain-la-Neuve, Belgium 2. Laboratoire d’Etudes en Géophysique et Océanographie Spatiales/Centre National d’Etudes Spatiales, 18 Avenue Edouard Belin, 31401, Toulouse Cedex 9, France 3. Institute for Atmospheric Science, Environment, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK 4. Laboratoire d’étude des Transferts en Hydrologie et Environnement, Université Joseph Fourier, BP53, 38041, Grenoble Cedex 9, France
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Abstract: | Sensitivity studies with regional climate models are often performed on the basis of a few simulations for which the difference
is analysed and the statistical significance is often taken for granted. In this study we present some simple measures of
the confidence limits for these types of experiments by analysing the internal variability of a regional climate model run
over West Africa. Two 1-year long simulations, differing only in their initial conditions, are compared. The difference between
the two runs gives a measure of the internal variability of the model and an indication of which timescales are reliable for
analysis. The results are analysed for a range of timescales and spatial scales, and quantitative measures of the confidence
limits for regional model simulations are diagnosed for a selection of study areas for rainfall, low level temperature and
wind. As the averaging period or spatial scale is increased, the signal due to internal variability gets smaller and confidence
in the simulations increases. This occurs more rapidly for variations in precipitation, which appear essentially random, than
for dynamical variables, which show some organisation on larger scales. |
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