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CR 52:193-211 (2012)  -  DOI:

Contribution to the CR Special: 'The regional climate model RegCM4'

Large-scale origins of rainfall and temperature bias in high-resolution simulations over southern Africa

M. B. Sylla1,*, F. Giorgi1, F. Stordal2

1Earth System Physics (ESP) Section, International Centre for Theoretical Physics (ICTP), PO Box 586, 34151 Trieste, Italy
2Department of Geosciences, University of Oslo, Box 1047 Blindern, 0316 Oslo, Norway

ABSTRACT: We use the Abdus Salam International Centre for Theoretical Physics (ICTP) regional climate model, RegCM3, nested in NCEP and ERA-Interim reanalyses (NC-RegCM and ERA-RegCM, respectively) to explore the effect of large-scale forcings on the model biases over a southern Africa domain at 25 km grid spacing. RegCM3 shows a generally good performance in simulating the location of the main rainfall features, temperature and synoptic scale circulation patterns, along with cloud cover and surface radiation fluxes. However, it shows a wet bias which varies substantially when fields from the 2 reanalysis products are used to drive the model, being greater in NC-RegCM than in ERA-RegCM. The wetter bias in NC-RegCM originates from larger moisture inflow, amplified cloud cover and upward motion caused by stronger low-level convergence. Similarly, negative temperature biases are present over most of the land areas, and the wetter NC-RegCM exhibits larger magnitudes of temperature bias. Surface flux analysis reveals that these lower temperature values in the NCEP-driven experiment are due primarily to the surface latent heat flux rather than cloud radiative forcing. As a result, the hydrologic cycle is more intense in the NC-RegCM than in the ERA-RegCM. Our results are relevant for a better understanding of the propagation of errors from the large-scale forcings to the regional model over the region of interest.

KEY WORDS: Rainfall bias · Large-scale conditions · Surface radiation budget · Surface climate

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Cite this article as: Sylla MB, Giorgi F, Stordal F (2012) Large-scale origins of rainfall and temperature bias in high-resolution simulations over southern Africa. Clim Res 52:193-211.

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