Influences of planetary waves upon the dynamics of the mesosphere and lower thermosphere.

摘要

Planetary Waves (PW) are global scale atmospheric oscillations usually with periods of 2–25 days and westward propagation with zonal wave numbers typically of 1–3. This project is to study the influences of PWs upon the mesosphere and lower thermosphere (MLT, 60–110 km), including the wave propagation, energy transfer and their climatology and variations.; Methodology has involved the analysis of data obtained from the Saskatoon MF (medium frequency) radar along with several other MF radars located from the arctic to equator; each of them can detect the local horizontal winds in the MLT region. The satellite measurements (UARS-HRDI) were also used in an attempt to obtain a global view of the waves.; Considering 16-day waves for example, they usually dominate the winter PW spectrum. Because of this, and since the 2-day waves have been extensively studied, the focus of this program of research has been upon the 16-day wave. The winter dominance of this wave is in good agreement with theoretical predictions that for westward travelling waves the vertical propagation is permitted only in a relatively eastward background wind. The wave longitudinal/latitudinal phase differences also indicate small horizontal wavenumbers (i.e. global scale features). The wave has been shown to be highly episodic in space and time in the MLT region. The wave vertical characteristics show significant energy deposition; also in some situations they show standing wave structures. A special experiment was carried out with the Global Scale Wave Model (GSWM) and the results were compared with the observations with special focus upon latitudinal variations. The comparisons show similarities in many aspects, but there are also dramatic differences in some situations that indicate the extreme sensitivity of the 16-day wave to the global background winds, and the complexity of the real atmosphere.; Energy sources directly associated with solar activity have also been considered for the explanation of some extra-long period (20–40 day) oscillations, which are comparable with the solar-rotation period. Finally, the modulation of gravity waves by 2 and 16-day waves, as well as non-linear interaction with tidal waves were investigated.