Thermal satellite images and boundary layer structures in desert marginal areas

A series of parallel striations has been observed on thermal satellite images of a desert marginal area in West Africa. The available climatic data suggest their identification as helical roll vortices of the type associated with the formation of cloud streets. This is because the wavelength of the striations conforms to the expected depth of the Atmospheric Boundary Layer (ABL) expected for such roll structures at the time of the image, and varies spatially according to the influence of ground surface roughness on ABL depth. Knowledge of helical roll vortices is usually derived from vertical temperature and wind profiles and radar reflectivity fields over time, whereas the image data presented here permit visualisation of the horizontal component, and thus examination of their interaction with surface phenomena. Association of the observed striations with systems of stabilised dunes in the study area, due to their similarity in length, direction and spacing, would support hypotheses of a causal relationship between helical roller vortices and linear dune systems.