中纬度冬季低热层潮汐非线性相互作用的MF雷达观测

采用武汉(30°N,114°E)MF雷达在2001年冬季的风场观测数据研究中纬度低热层大气潮汐之间的二阶非线性相互作用.经向风场的Lomb-Scargle归一化振幅谱表明,周日、半日和8 h潮汐是中纬冬季中层顶区域占优势的大气扰动;此外6 h潮汐也清晰可见.双相干谱分析揭示大多数显著的双相干谱峰代表潮汐谐振分量之间的相位互相关或单个潮汐分量的自相关.对随时间变化的潮汐垂直波长的比较发现,实际观测的8h潮汐垂直波长与假定的由观测的24 h潮汐和12 h潮汐非线性相互作用产生的8 h潮汐的理论垂直波长具有明显的一致性.在94.0°98.0 km高度范围,周日、半日和8 h潮汐之间不仅存在明显的相位相关和垂直波数相关,且它们的振幅随时间变化也显示出振荡幅值相近、振荡相位同步或反相的相关性,表明它们之间已经发生了二阶非线性相互作用.但是在94.0 km以下,三个潮汐分量之间的各种相关性随高度的下降变得越来越弱,因此潮汐二阶相互作用更可能是一种局地和暂态的现象.

MF Radar Observations of Nonlinear Interactions Between Tides in the Mid-latitude Winter Lower Thermosphere

Data obtained from Wuhan MF radar in winter of 2001 are used to study the quadratic nonlinear interactions between tides in lower thermosphere. It is observed that diurnal, semidiurnal and terdiurnal tides are the prominent perturbations in the meridional wind component near mid-latitude winter mesopause region, and the 6h tide is clear. By bicoherence spectrum analysis, it is revealed that most prominent bicoherence peaks stand for phase correlation between tidal harmonics or self-coherence of a single tidal wave. By examining the vertical wavelength time variations, a significant correlation is found between the vertical wavelength of the observed 8 h tide and that of the supposed nonlinearly generated one by the interaction between 12 and 24 h tides. In the interval of 94.0~98.0km, there exist not only a certain phase correlation and vertical wavenumber correlation but also a strong amplitude correlation of the oscillatory amplitudes equivalent and oscillatory phases synchronous or reversed between the prominent tides, indicating a wave-wave quadratic interaction has occurred. However, below 94.0 km, the various correlations between tides grow weaker and weaker with descending height and hence the tidal quadratic interaction is more likely a local and temporary phenomenon.