The island of St. Vincent and the other Windward Islands in the southeastern Caribbean were chosen as a field site for the study of weak mountain wakes. By the authors' definition, a "weak wake" forms when the potential vorticity generated by a mountain is not strong enough to advect itself into eddies; rather, it is simply advected downstream by the ambient flow. GOES-8 and Landsat sunglint images unambiguously revealed that the mountainous Windward Islands have remarkably long straight wakes. The length of St. Vincent's wake exceeds 300 km although its width is only 20 km. Near the islands, the wake structures reflect the details of the island topography. These wakes do not exhibit any obvious diurnal effect. Boat surveys in the lee of St. Vincent confirmed the existence of features seen in the images: the sharp wake boundary, the small valley-induced jet embedded in the near wake, and the absence of any reverse flow. Aircraft surveys gave evidence of descent over the island and showed that the wake air is relatively warm and dry. The length of the wake (L) agrees with the formula L = H/2CD (where H is the wake depth and CD, is the surface drag coefficient), implying that the reacceleration of the wake air is caused by the ambient streamwise pressure gradient rather than by lateral entrainment of momentum or geostrophic adjustment. Two numerical models were used to simulate St. Vincent's wake, a single-layer hydrostatic model and a 3D nonhydrostatic model. Both models indicated that air descent, acceleration, wave breaking, and weak potential vorticity generation occur over the island, causing a long straight wake.
|Original language||English (US)|
|Number of pages||18|
|Journal||Journal of the Atmospheric Sciences|
|State||Published - Mar 1 1997|
ASJC Scopus subject areas
- Atmospheric Science