CR 68:243-255 (2016)  -  DOI:

Contribution of cold fronts to seasonal rainfall in simulations over the southern La Plata Basin

Eduardo Marcos de Jesus1, Rosmeri Porfírio da Rocha1, Michelle Simões Reboita2,*, Marta Llopart3,4, Lívia Márcia Mosso Dutra1, Armelle Reca C. Remedio5

1Department of Atmospheric Sciences, University of São Paulo, Rua do Matão, 1226 Cidade Universitária, São Paulo 05508-090, Brazil
2Natural Resources Institute, Federal University of Itajubá, Av. BPS 1303, Itajubá, Minas Gerais 37500-903, Brazil
3Departamento de Física, Universidade Estadual Paulista (UNESP), Bauru, São Paulo 17033-360, Brazil
4Centro de Meteorologia de Bauru (IPMet), Bauru, São Paulo, Brazil
5Climate Service Center Germany (GERICS) Chilehaus, Eingang B, Fischertwiete 1, Hamburg 20095, Germany
*Corresponding author:

ABSTRACT: This work investigates how regional climate models REMO and RegCM4 simulate the frequency of cold fronts (CFs) over southern Brazil and the contribution of these systems to the seasonal precipitation over the southern part of La Plata Basin (SLPB) in South America. Simulations were driven by the ERA-Interim reanalysis and compared with local observations (from Rio Grande station; RG), ERA-Interim, and rainfall analysis from the Climate Prediction Center (CPC). CF identification was carried out objectively by considering (1) the turning of the meridional wind component from north to south and (2) a decrease in air temperature between 1 d before and 1 d after the CF passage. For the period 1991-2008, a mean of 55.3, 53.1 and 51.8 CFs yr-1 were identified, respectively, for RG (observed), REMO and RegCM4. These values show a small bias in the simulated annual frequency of CFs (around -5%), but the underestimation reaches -17% during summer in the RegCM4. In the simulations, it is possible to find some association between seasonal bias of rainfall and the bias of rainfall during CF periods (defined as extending from 2 d before to 2 d after the CF passage) over SLPB. Except in summer, RegCM4 presents stronger biases than REMO for rainfall for both CF periods and overall seasonal climatology. For the winter season, the CF composites indicate that deeper low pressure and larger availability of moisture at low levels (from 2 d before to the day of the CF) contribute to the small underestimation of rainfall in REMO (-5%) compared with RegCM4 (-25%).

KEY WORDS: Cold fronts · Precipitation · La Plata Basin · Regional climate models

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Cite this article as: de Jesus EM, da Rocha RP, Reboita MS, Llopart M, Mosso Dutra LM, Remedio ARC (2016) Contribution of cold fronts to seasonal rainfall in simulations over the southern La Plata Basin. Clim Res 68:243-255.

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