Journal of Atmospheric and Solar-Terrestrial Physics 66 (2004) 623–636 www.elsevier.com/locate/jastp 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 P.P.Batista ∗ ,B.R.Clemesha,A.S.Tokumoto,L.M.Lima Instituto Nacional de Pesquisas Espaciais, INPE, S˜ ao Jos e dos Campos SP, Brazil Received 12 February 2003; accepted 20 January 2004 Abstract Zonal and meridional winds in the region of the upper mesosphere and lower thermosphere (MLT) have been measured withameteorradaratCachoeiraPaulista,Brazil(22:7 ◦ S,45 ◦ W)duringtwoyears,fromMarch1999toFebruary2001.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 dierent 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. c  2004 Elsevier Ltd. All rights reserved. Keywords: Atmospheric tides; Meteor radar; Meteor region; Mean winds 1. Introduction The knowledge of the climatology of the winds in the MLT region is of great importance. The motions in this region of the atmosphere are dominated by atmospheric tides, planetary waves and gravity waves, in addition to long-term variations (annual and semiannual). Tides and gravity waves have their origin in the troposphere and stratosphere and propagate upward transferring energy via dissipation to higher regions, modifying the basic circula- tion in these regions. This climatology is suciently well known in middle and high latitudes, mainly in the northern ∗ Corresponding author: Tel.: +55-12-3945-7143; fax: +55-12- 3945-6952. E-mail address: pbatista@laser.inpe.br (P.P. Batista). hemisphere(Mansonetal.,1985,1989,1991)butthereisa big gap mainly in equatorial and subtropical regions of the southern hemisphere. Satellite measurements have played, of course, an important role in dening the global climatol- ogyoftheatmospherictides,butthesehavetheirlimitations. The HRDI and WINDII instruments on the UARS satellite have provided invaluable information on the global struc- ture of atmospheric tides (see, for example, McLandress et al., 1996a, 1996b, Bruinsma et al., 2002; Manson et al., 2002).Thesemeasurements,however,take36daystocover a complete diurnal cycle and, although covering a wider height range than the meteor radar during the day, at night they are limited to the OI557.7 emission region, approxi- mately 90-110 km. As a result of this, there is a continuing needforground-basedmeasurementstoprovidecontinuous coverageatxedlocations.Theoreticalmodels(Forbesand Vial, 1989; Haganetal.,1995,1999,2001)predictthatthe 1364-6826/$ - see front matter c  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2004.01.014