The role of air-sea fluxes and upper ocean mixing on the mixed layer response: A numerical investigation

S. Daniel Jacob



Oceanic fresh water transport has been shown to to play an important role in the global hydrological cycle. With more than 70% of global evaporation and precipitation occuring over world's oceans, it has also been pointed out that small changes in these will cause major changes in the terresterial water budget. Sea Surface Salinity (SSS) is representative of the surface fresh water fluxes and the upcoming NASA Aquarius mission will provide excellent spatial and temporal SSS coverage to better estimate the net transfer. However, SSS is also controlled by advection and mixing processes, therefore the main objective of this study is to understand and quantify various mechanisms controlling SSS in relation to surface fresh water fluxes over interannual time scales. Results from a near-global numerical model configured with different mixing schemes for different forcing data sets will be presented for no SSS relaxation to identify regions of maximum variability.

The second part deals with upper ocean response during extreme events such as hurricanes. Prior observational and numerical studies indicated that the oceanic mixed layer budgets are strongly affected by the choice of turbulent closure schemes. This is particularly important in a coupled hurricane-ocean prediction system, because the surface heat fluxes to the atmosphere are modulated by oceanic mixing in the directly forced region. Results from two stand-alone ocean models will be presented for forcing associated with hurricane Gilbert (1988) in the Gulf of Mexico. In addition, rain rates of more than 20 mm/hr have been estimated in hurricanes from remotely sensed data. SSS changes in the model for such extreme fresh water forcing will also be discussed.