Structure of the mean winds and tides in the meteor region over Cachoeira Paulista, Brazil (22.7°S,45°W) and its comparison with models

Abstract

Zonal and meridional winds in the region of the upper mesosphere and lower thermosphere (MLT) have been measured with a meteor radar at Cachoeira Paulista, Brazil (22.7°S, 45°W) during two years, from March 1999 to February 2001. Winds were calculated with temporal resolution of 1 h and vertical resolution of 2 km from 80 to 100 km height. Monthly means were calculated and the wind structure was decomposed into the mean, diurnal, semidiurnal and terdiurnal components. The mean wind showed the zonal component to dominate with westward wind above 90 km from May to October, a dominance of an eastward wind from October to April between 80 and 100 km and a small interannual variation. The meridional wind shows a simple structure with northward wind from October to April and Southward wind from May to September. The dominant mode in the diurnal tide has a wavelength ranging from 25 to 30 km, which is consistent with the S1,1 mode, in good agreement with the GWSM model. Large interannual variations and different phases were noted during November and December. The diurnal amplitudes are in general smaller than those predicted by the model, mainly during October. The semidiurnal amplitudes are in general, greater than those for the model, and the phases show some vertical propagation or are almost evanescent. The terdiurnal component although weak shows good height and interannual coherence. © 2004 Elsevier Ltd. All rights reserved.