Effects of spatial resolution and temporal sampling of air-sea boundary variables on air-sea heat flux estimates: implications to NWP nowcast and forecast

Recent studies suggest that small-scale SST variability associated with mid-latitude western boundary currents influence air-sea latent and sensible heat fluxes, thereby affecting the variability of atmospheric fronts with implications to NWP nowcast and forecast. Currently, these fluxes are often estimated from satellite measurements of wind speed, SST, surface air temperature and humidity that often have heterogenous and coarse spatial resolutions and with offset in measurement times (coming from different satellites). These factors are widely perceived to degrade the quality of the estimated air-sea heat fluxes. The assimilation of these measurements or the associated radiance in NWP models may impact nowcast and forecast. Understanding the effects of spatial resolution and temporal sampling of the air-sea boundary-layer variables on air-sea heat fluxes is important to defining the requirements of related satellite missions for the future. To assess these effects, a 3-km resolution WRF model simulation was performed for the Gulf Stream extension in the North Atlantic, forced by JPL's Multi-scale Ultra-high Resolution (MUR) SST product. Latent and sensible heat fluxes are estimated from the WRF model output by decimating the input variables for the heat-flux calculation to different spatial resolutions and with different temporal offsets up to a few hours. Significant impacts of spatial resolution and temporal offset on the heat flux estimates are found, especially due to temporal offset. The results underline the importance of coincident measurements of air-sea boundary variables as well as the need for improved spatial resolution.