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CR 52:253-265 (2012)  -  DOI:

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

Effects of RegCM3 parameterizations on simulated rainy season over South America

Rosmeri Porfirio da Rocha1,*, Santiago Vianna Cuadra2, Michelle Simões Reboita3, Luiz F. Kruger1, Tércio Ambrizzi1, Nisia Krusche4

1Department of Atmospheric Sciences, University of São Paulo, Rua do Matão, 1226, Cid. Universitária, São Paulo, SP 05508-090, Brazil
2Department of Atmospheric Sciences, Federal Center of Technological Education Celso Suckow da Fonseca (CEFET/RJ), Av. Maracanã, 229, Rio de Janeiro, RJ 20271-110, Brazil
3Environmental Resource Institute, Federal University of Itajubá (UNIFEI), Av. BPS, 1303, Itajubá, MG 37500-903, Brazil
4Computer Science Center, Federal University of Rio Grande, Av. Itália, km 8, Rio Grande, RS 96201-900, Brazil

ABSTRACT: The impacts of change in the Grell convective scheme and biosphere−atmosphere transfer scheme (BATS) in RegCM3 are described. Three numerical experiments (RegZhang, RegClaris and RegArain) are conducted to reduce the RegCM3-Grell rainfall underestimation over tropical South America. The simulation referred to as RegZhang follows modifications made by Zhang et al. (2008) in the BATS. The RegClaris combines the RegZhang BATS parameters with a reduction of water drainage at the bottom of the subsoil layer in the regions covered by the tropical rain forest and a shorter convective time period for the Grell scheme. The RegArain considers this same modification in the Grell scheme, but uses a deeper total soil column and a deeper root system in the BATS. After the first year of simulation, the soil water content in RegZhang is progressively drained out of the soil column resulting in a deficit of rainfall in the Amazon. The RegClaris and RegArain, on the other hand, simulate a similar rainfall annual cycle in the Amazon, showing substantial improvement not only in phase but also in intensity. This improvement is partially related to an increase in evapotranspiration due to a larger availability of water in the soil column. A remote effect is also noted over the La Plata Basin region, where the larger summer rainfall rate may be related to the increase in moisture transport from the Amazon. Wind- and rainfall-based indices are applied to identify South American monsoon (SAM) timing. The RegClaris rainfall rates are adequate to identify the onset and the demise of SAM according to the observed data, whereas the rainfall deficit in RegZhang is associated with a delay in the onset and an early demise of the SAM.

KEY WORDS: Regional climate model · Annual cycle of precipitation · South American monsoon · Land-surface model · Amazon Basin hydrology

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Cite this article as: da Rocha RP, Cuadra SV, Reboita MS, Kruger LF, Ambrizzi T, Krusche N (2012) Effects of RegCM3 parameterizations on simulated rainy season over South America. Clim Res 52:253-265.

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