Characteristics of Atmospheric Surface Ducts in the Brazilian Semiarid

The objective in this work was to evaluate the influence of Upper Level Cyclonic Vortices (ULCV) upon the atmospheric boundary layer structure and the establishment of favorable conditions for surface duct (SD) formation. Refractivity gradient and SD thickness and intensity values were obtained with a basis on data of atmospheric soundings made in the month of January, at 12 UTC, at the altitude station of Petrolina-PE, in the period from 2000 to 2014. The results indicate that the number of SD is considerably higher in months with rainfall deficiency. In January 2004, an extremely rainy month, the SD are less intense in comparison with those observed in 2001 and 2007, two years characterized by a large reduction in the rainfall volume typically observed in the month of January. In the absence of intense convective activity, the influence of local atmospheric conditions becomes dominant in SD formation. The persistence and geographic position of ULCV are predominant factors in SD formation. No evidences were found of a relationship between the frequency of ULCV in the region of study and significant changes in the thickness and/or intensity of the SD.