Sea surface temperature‐related response of precipitation in northern South America according to a WRF multi‐decadal simulation

Abstract

Precipitation, low‐level flow and atmospheric moisture transport fields over the Intra‐Americas region from a Weather Research and Forecasting model (WRF) multi‐decadal simulation are presented. The period of analysis is 1982–2012, and the focus is on mean monthly states and their variability. WRF results are compared to global precipitation products and to the Interim Reanalysis from the ECWMF (ERA‐Interim). An analysis of the coupling between precipitation over northern South America and regional scale sea surface temperatures (SSTs) and winds within ERA‐Interim and WRF is also presented. Over land, precipitation biases in WRF are mostly positive, especially over Central America and northern South America. This bias is associated with an excess in atmospheric moisture convergence in WRF compared to ERA‐Interim, which in turn is related to stronger low‐level circulation structures and differences in the moisture transport field between WRF and ERA‐Interim at the regional scale. The largest differences in the flow are observed over the eastern Pacific, where the flow is correlated with precipitation over southern Mexico, Central America and northern South America during the boreal summer. During early winter, correlation patterns of WRF precipitation and SST anomalies over the tropical Pacific are substantially weaker over western Texas and northwestern South America compared to the coupling between the global precipitation products and observed SSTs. For northwestern South America, the low correlation seems to be associated to a lack of coupling between regional scale winds and SST anomalies. During the boreal summer, the coupling between Caribbean SSTs and precipitation over parts of Mexico and Central America is stronger in WRF compared to observation‐based products.