The impact of SST on the wind and air temperature simulations: a case study for the coastal region of the Rio de Janeiro state

Abstract

The impact of Sea Surface Temperature (SST) on the wind and air temperature numerical simulations over the coastal region of the state of Rio de Janeiro, Brazil, was investigated using the Weather Research and Forecasting (WRF) model. The study period comprised January 24–26, 2014, characterized by the occurrence of coastal upwelling. Two numerical experiments were performed. The first, called EGFS, used the Global Forecast System (GFS) results to prescribe the initial and boundary conditions. In the second, called EMUR, the SST was replaced by the Multi-scale Ultra-high-Resolution SST (MUR SST). The experiments showed significant differences between the SST fields, being higher than 10 °C. Through the comparison with observations, we verified that the upwelling was better represented in the EMUR, which consequently generated improvements in the temperature at 2 m above ground level (AGL) over this region. In the offshore region, over areas with higher SST, the wind speed at 10 m AGL was stronger, and opposite behavior was observed over low SST areas. In addition, in regions with higher SST differences between the experiments, differences of wind direction at 10 m AGL higher than 90° were detected. The SST influence on the air temperature and wind speed profiles was significant up to 300 and 900 m, respectively. The comparisons between the wind observations with the numerical results show that the land–sea breeze simulation (thermal forced) was underestimated in relation to the synoptic forcing (South Atlantic Subtropical Anticyclone), even with significant SST differences between experiments.