VHF RADAR OBSERVATION OF THE SEMIDIURNAL TIDE IN THE SUMMER POLAR MESOSPHERE

Data obtained from the mobile SOUSY VHF radar at Andthya/Norway(69°N,16°E) during the MAC/SINE campaign in summer 1987 have been used to studythe structure characteristics and variability of the semidiurnal tide in the polarmesosphere. It is shown that the spectral peak corresponding to the semidiurnaltide dominates and persists almost uninterruptedly in time. The correspondingfrequency often deviates from 1/12 c.h^-1. This likely represents a temporary or disturbed state. The amplitude of the stable semidiurnal tide increases rapidly withheight and shows a saturation behavior at the height of about 87.9 km. The phasefront of the tide moves downward, indicating the associated energy flux transportsupward. The phase of the meridional component often leads that of the zonal component about T/4-π/2(equivalent to 1.5-3 h), resulting in a clockwise hodographof the wind vector with respect to time. The values of wave-associated parametersare obtained by a harmonic analysis in which the variable frequency correspondingto spectral peak is traced. By and large, the time variation trends of the tide inthe zonal and meridional components are similar, but display an anisotropy to someextent.