Using a second order turbulent closure model for gravity waves

Turbulence can be a significant factor over mountains, due in part to shear from gravity waves. Aircraft encounter turbulence over mountainous terrain more frequently than over flat terrain by about an order of magnitude (Wallace and Hobbs, 1977). While turbulence itself cannot be predicted, statistical properties of turbulence such as fluxes can.

My PhD project involves using a Boussinesq numerical model for predicting gravity waves over mountains, adjusted to include turbulent fluxes. In this model, the independant variables are split into three components: a background state, perturbations due to the orography, and averaged turbulent fluxes.

Prognostic equations will be used to solve for the turbulent fluxes, which will require assumptions (or closure schemes) for unsolvable variables such as third moment terms and terms involving turbulent pressure. These unsolvable terms will be approximated mainly by down-gradient theory and return-to-isentropy.

The model will also be compared with observations. Radiosonde soundings will provide the background flow, and the resulting turbulent fluxes will be compared to fluxes calculated from aircraft data.