Short period oscillations in mesosphere

Abstract

Long sequences of the hourly average zonal and meridional wind components obtained by MF spaced antenna radars at Davis (69^oS, 78^oE), Buckland Park (34^oS, 138^oE) and Christmas Island (2^oN, 157^oW) are spectrally analyzed to study the short period oscillations in mesospheric winds. Data lengths covering a minimum of four years at each of the stations, five altitudes used for averaging (84-92 km) and the windows of 10, 20 and 40 days used in estimating power spectra give high reliability and spectral resolution. Apart from the tidal components at 24, 12, 8 and 6 h there are oscillations with periods ranging between -4.8 h and 12 h.Moving power spectra are obtained to study the seasonal dependence of the short period (smaller than 12 h) oscillations. The wave activity is strongest during June solstice and weakest during equinoxes at each of the locations. The presence of similar features at high, mid and low latitudes indicates the global nature of such oscillations. The seasonal dependence of the wave activity is in agreement with the recently reported observations of waves with periods between 7.5 and 10.5 h seen in the meteor radar data at south pole. Oscillations with periods of 4.9-5.2 h and 7.2-7.5 h are also seen.