Coupled surface winds and ocean surface diurnal variability using WRF

Diurnal variability of sea surface temperatures, in which afternoon heating of the sea surface increases heat transfer from the ocean to the atmosphere, is rapidly being recognized as a vital component in driving local fluxes and atmospheric circulations in numerical weather prediction (e.g. Noh et al., 2011). In low surface wind speed environments, diurnal heating develops as a result of low mechanical mixing in areas where solar radiation absorption is high. In specific cases, the SST heating resembles a “diurnal sea surface temperature gradient”, where heating appears as thin streaks up to 1500 km long with SST gradients typically less than 1°C/100 km over the course of a few hours (e.g. Stuart-Menteth et al., 2003). While it is clear that there is a strong relationship between wind stress and more static sea surface temperature gradients (i.e. the Gulf Stream), the goal here is to determine the biases in wind and wind stress curl fields by incorporating a diurnal sea surface temperature gradient.

Case study simulations of the coupled influences of diurnal sea surface temperature variations and wind stress curl and divergence are examined through the use of two sea surface temperature parameterizations in the Weather Research and Forecasting (WRF) model. First, an idealized 7-day simulation will consist of artificially modified SSTs in the central Atlantic with a consistent heating pattern from day to day. Using an idealized heating pattern in the SST field will help address the integrity of developing atmospheric gravity waves emanating from SST heating found in preliminary results. Second, a more realistic simulation for the same domain will be performed in which SSTs will be updated according to the skin sea surface temperature parameterization within WRF by Zheng and Beljaars (2005). This will help in identifying consistencies between coupled feedbacks on heating of the atmosphere, horizontal pressure gradients, and the possible self-limiting nature of surface winds and diurnal variability of the ocean.