Impact of SST Resolution on Numerical Sea Breezes over Complex Coastal Regions

Sea breezes are mesoscale atmospheric coastal circulations that develop in response to diurnal variations in the land-sea thermal gradient. Accurate numerical model hindcasts and forecasts of sea breezes, used to study and predict these circulations, are important for a variety of communities beyond the atmospheric sciences. For example, sea breezes can influence marine processes such as oceanic upwelling, estuarine circulation, and air-sea fluxes, as well as impact the energy, aviation, and air quality industries. Sea surface temperature (SST) used in the mesoscale numerical model can influence simulated sea breeze circulations. In this study, a series of sensitivity experiments are performed to highlight the impact of the horizontal resolution of SST on simulated sea breeze dynamics.

The 21 August 2013 coastal Connecticut sea breeze event is simulated using the Weather and Research Forecasting (WRF) model, initialized with the 32 km North American Regional Reanalysis (NARR) for atmospheric conditions. Sea surface temperature sensitivity experiments compare a spatially uniform SST (22˚C), NARR (32 km) spatially varying SST, and the GHRSST Global 1-km SST (G1SST; 1km) spatially varying SST. The uniform SST experiment value is the average of the G1SST within Long Island Sound for the day of the sea breeze event. In all simulations, the SST is temporally constant.

Sea breeze circulations are weakly sensitive to the resolution of the offshore SST, though the inland propagation distance of the sea breeze front varies among the sensitivity experiments. While the surface fluxes respond to the varying SST products, the impact on the overlying air temperature is confined to the lowest 100 m of the marine atmospheric boundary layer (MABL) due to the relatively high stability limiting vertical mixing. However, differences in daily accumulated sensible and latent surface heat fluxes between SST products can be as large as 200%, which may impact coastal atmospheric and oceanic phenomena on longer time scales.