Very High Resolution Simulations of Lee Waves in the Falkland Islands

Trapped lee waves form in the lee of terrain when conditions of stratification and/or vertical shear above mountain tops act to reflect and duct gravity waves in the lower troposphere, often accompanied by turbulent `rotor' conditions. In the Falkland Islands, the terrain is relatively modest (~ 600 m peak height), while lee wave wavelengths are typically rather short (~ 5 km). Nevertheless, rotors constitute a severe problem for aviation at this remote location. The strongest lee waves occur in northerly flows which frequently contain a strong low-level inversion, whose high stability is responsible for the short wavelengths observed and the intensity of turbulent events experienced, with the potential to create intense downslope winds and flow dynamics resembling a hydraulic jump under more severe conditions.

While in many locations and circumstances, operational models currently begin to represent lee waves realistically, the small scale of the geography and wave response here are expected to make higher demands on model resolution and parametrisations. Nested simulations have therefore been performed to assess the ability of pseudo-operational configurations to model wave events over the islands as a function of resolution, by comparing to results from an extensive field campaign. The range of resolutions used also offers the opportunity to examine the impact of surface and terrain inhomogeneity on the flow as it passes over the island.