The Impact of the Sea Surface Temperature Resolution on Mesoscale Coastal Processes during GALE IOP 2

Abstract

The Pennsylvania State University-NCAR Mesoscale Model is used to examine the sensitivity of the structure and evolution of mesoscale coastal phenomena to the sea surface temperature (SST) distribution in the vicinity of the Gulf Stream during intensive observation period 2 (IOP 2) of the Genesis of Atlantic Lows Experiment (GALE). Experiments are performed with three different SST analyses: A 1) a high-resolution 14-km analysis, 2) a medium-resolution 275-km analysis, and 3) a coarse-resolution 381-km analysis. The results indicate that numerical simulations of mesoscale phenomena embedded in the marine atmospheric boundary layer (MABL) in the vicinity of the Gulf Stream are very sensitive to the SST distribution. The total (sensible and latent) average heat fluxes differ by less than 15% among the three experiments; however, the mesoscale distributions of the oceanic surface heat fluxes differ substantially. As a result of large differences in the lower-tropospheric diabatic heating, significant dissimilarities occur among the three experiments in terms of the intensity and movement of the north-wall MABL front, MABL structure, coastal front, cyclone, and precipitation. The maximum values of diagnosed quantities (e.g., vorticity, divergence, thermal gradients, and frontogenesis) in the vicinity of the Gulf Stream vary by as much as a factor of 8 among the three simulations. Also, the lower-tropospheric geostrophic forcing along the coast is relatively weak in the two simulations that used lower-resolution SST analyses. This weak geostrophic forcing in the lower-resolution SST experiments results in the development of a low-level jet that is weaker than observed and simulated in the experiment with the high-resolution analysis. Among the three experiments, the high-resolution SST analysis simulation best captures the analyzed intensity, structure, and movement of the mesoscale coastal phenomena. Thus, the use of high-resolution SST analyses in research and operational mesoscale models may be essential in some cases for the accurate prediction of coastal cyclones and their associated mesoscale structures.