极区夏季中间层半日潮汐的VHF雷达观测

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

采用德国SOUSYVHF雷达观测数据，研究了极区夏季中间层半日潮汐的结构和变化特征．纬向和经向风的动态Lomb－Scargle诺表明，半日潮是中间层高度上占支配地位的波动，其谱峰对应的频率一般与1／12c·h－1有偏离，说明它们经常处在被扰动状态．稳定的半日潮损帽院高度增加而迅速增长，在87．9km高度附近达到饱和；经向分量的相位一般比纬向分量的相位超前π／4－π／2，从而水平扰动速度关县端点随时间变化的轨迹显示出顺时针方向旋转的特征．半日潮汐特征参量在纬向和经向风中随时间的变化在基本趋势一致的基础上显示出一定程度的各向异性．

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.