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Tropical-temperate interactions over southern Africa simulated by a regional climate model

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Abstract

The Weather Research and Forecasting model (WRF) forced by ERA40 re-analyses, is used to examine, at regional scale, the role of key features of the local atmospheric circulation on the origin and development of Tropical Temperate Troughs (TTTs) representing a major contribution to South African rainfall during austral summer. A cluster analysis applied on 1971–2000 ERA40 and WRF simulated daily outgoing longwave radiation reveals for the November–February season three coherent regimes characteristic of TTTs over the region. Analyses of WRF simulated TTTs suggest that their occurrence is primarily linked with mid-latitude westerly waves and their phasing. Ensemble experiments designed for the case of austral summer 1996/1997 allow to examine the reproducibility of TTT events. The results obtained illustrate the importance of westerly waves phasing regarding the persistence of rain-producing continental TTT events. Moreover, oceanic surface conditions prevailing over the Agulhas current regions of the South West Indian Ocean (SWIO) are also found to influence TTT persistence for regional experiments with an oceanic mixed layer, warmer sea surface temperatures being associated with increased moisture advection from the SWIO where latent heat release is enhanced, favoring baroclinic instability and thus sustaining convection activity locally.

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Acknowledgments

N. Vigaud would like to acknowledge the financial support of the University of Burgundy (Dijon, France) through the BQR2010-005 program. Calculations were performed using HPC resources from DSI-CCUB, University of Burgundy. WRF was provided by the University Corporation for Atmospheric Research (http://www.mmm.ucar.edu/wrfusers/download/getsource.html). ECMWF ERA40 re-analyses used in this study were obtained from ECMWF Meteorological Archival and Retrieval System (MARS) data server, GPCP rainfall estimates and WRC rain-gauges observation from the referring institutions.

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  1. Centre de Recherches de Climatologie, UMR 6282 Biogéosciences CNRS/Université de Bourgogne, Dijon, France

    N. Vigaud, B. Pohl & J. Crétat

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  1. N. Vigaud
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Vigaud, N., Pohl, B. & Crétat, J. Tropical-temperate interactions over southern Africa simulated by a regional climate model. Clim Dyn 39, 2895–2916 (2012). https://doi.org/10.1007/s00382-012-1314-3

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