Abstract
Abstract. Mesospheric winds observed with a meteor radar at Cariri (7.4° S, 36.5° W), Brazil, during the period of July 2004 to June 2005, show a clear semiannual oscillation known as the Mesospheric Semiannual Oscillation (MSAO), which maximizes in the zonal mean wind mainly at 82 km, with amplitude decreasing with height. Maximum westward winds for the MSAO occurred in March and September. The meridional wind, on the other hand, presented a clear annual variation maximizing in December. On average, the amplitude of the meridional MSAO was smaller than the zonal MSAO component. Comparison with models shows on occasions that there are significant differences between the observed winds and the CIRA (Cospar International Reference Atmosphere) and HWM93 (Horizontal Wind Model) models. In addition, diurnal and semidiurnal parameters were calculated and compared to the GSWM model. Other results observed during one year of data are presented in this work.
Highlights
Routine observations of mesospheric wind in the equatorial region by meteor radar have become frequent since the beginning of this decade
The wind calculated by the empirical Horizontal Wind Model 93 (HWM93) for Cariri was compared to the observed wi3nd3 at Cariri
Burrage et al (1996) used 3 yr of data from the High Resolution Doppler Imager (HRDI) on the Upper Atmospheric Satellite (UARS) to study the Mesospheric Semiannual Oscillation (MSAO), and reported an amplitude maximizing at 35 m/s near 82 km in the equatorial region
Summary
The dynamics of the MLT in the equatorial region is quite different to mid-latitudes. The wind data obtained by the meteor radar were analyzed separately for the zonal and meridional components. The monthly average zonal wind is basically westward, exinteractions between tides, gravity and planetary waves as responsible (or not) for the semiannual oscillation, have been recently considered, producing better theoretical descriptions of the tides as a function of altitude, season and latitude (Geller et al, 1997, Forbes, 1982; McLandress, 2002a,b; Hagan et al, 2002; Hagan et al, 2003). At 82 km antennas (5 in total) for reception and a 3-element yagi transmitting antenna This particular SKiYMET operates at a frethe wind showed the lar2g4est semiannual amplitude, reaching 22.6 m/s, with a maximum westward intensity of about quency of 35.24 MHz and the output power is 12 KW peak. Note that the amplitudes present a considerable error at 88–94 km, so it is necessary to avoid drawing conclusions about this component at this altitude
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