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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Acknowledgments
E. Vanvyve is sponsored by the Belgian National Fund for Industrial and Agricultural Research. N. Hall is supported by the CNRS. C. Messager is supported by NERC grant NE/B505538/1. S. Leroux is sponsored by the French Ministry of “Enseignement Supérieur et Recherche”. J.-P. van Ypersele is a professor at the Université catholique de Louvain. All model simulations were realised with the CNRS-IDRIS computing resources (Institut du Développement et des Ressources en Informatique Scientifique, France). The authors thank the European Centre for Medium-Range Weather Forecasts (United Kingdom) for its dataset used as driving fields for the model. This study forms part of the international African Monsoon Multidisciplinary Analysis (AMMA) project, see http://www.amma-international.org for details.
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Vanvyve, E., Hall, N., Messager, C. et al. Internal variability in a regional climate model over West Africa. Clim Dyn 30, 191–202 (2008). https://doi.org/10.1007/s00382-007-0281-6
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DOI: https://doi.org/10.1007/s00382-007-0281-6