Mountain Waves and Rotors in East Falkland

In the Falklands field experiment, that took place from November 2000 to October 2001, the occurrence of rotor activity was observed for roughly half the number of episodes of northerly flow. All the severe weather observed was coupled to a temperature inversion near the mountain top and a regime diagram relating the Froude number and the ratio of mountain height to inversion height was developed. In it, three different types of flow regimes were identified: (i) strong downwind acceleration; (ii) strong downwind acceleration and variable flow; (iii) weak downwind acceleration. During northerly flow, the radiosonde profiles are downwind soundings thus, the inversion height and strength are not representative of the undisturbed flow. This study will show that the basic flow patterns and the underlying structures can also be determined through Principal Component Analysis.

The different flow regimes are simulated with the research model MesoNH where a series of nested simulations for selected days are conducted. The ERA40 dataset provided the reference state for the model upstream conditions and the innermost grid has 100m resolution. The model results are compared with the ground observations of specific days focusing on the temporal and spatial variations observed in the wave field, the location of separation points and the three-dimensional structure of rotors.