Sensitivity of precipitation and atmospheric low-level circulation patterns to domain size and choice of parameterization schemes in RegCM4.4 over Central America

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Abstract
The sensitivity of regional climate model simulations to domain size and position is becoming increasingly important for generating reliable climate scenarios. In this study, the Central America CORDEX domain (CCA) at 50 km horizontal resolution with a relaxation zone of 10° around the boundaries (CCA+) was taken as the basis to increase domain size in the RegCM4.4 model. The low-level circulation and precipitation patterns over Central America, the western Caribbean Sea, and the eastern tropical Pacific do not show strong sensitivity to domain size changes for an area increment of 18, 32, and 52% with respect to the size of CCA+. The physical configuration in RegCM4.4 has a greater impact on the representation of relevant climate characteristics and atmospheric processes. Simulated 925 hPa winds over the Caribbean low-level jet (CLLJ) region show unrealistic winter and summer intensities, especially in July. Similar issues were found in other studies for the CCA domain, using different models and physical configurations. A reduction of the critical Richardson number in the selected planetary boundary layer scheme resulted in little change in the strength of the summer component of the CLLJ. The model simulations do not completely capture key regional precipitation patterns such as the mid-summer drought, due to limitations in adequately representing low-level circulation. However, simulations using the Grell cumulus parameterization perform relatively better than those using a mixed scheme (Grell over land-Emanuel over ocean).

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