Non-linear interaction of tides and planetary waves in the mesosphere and lower thermosphere: Observations over Europe

Observations of tidal modulations measured by meteor radars situated in UK (53.5 degreesN, 3.9 degreesW), Bulgaria (42.5 degreesN, 26.6 degreesE) and Sweden (67.9 degreesN, 21.1 degreesE) are shown in the present study. The observations indicate that the nonlinear interaction between tides and planetary waves contributes significantly to the tidal variability at planetary wave periods in the MLT region. The most frequently observed tidal modulations have periods of the well-known normal modes with periods of 2, 5, 10, 16 and 25-27 days. The planetary wave zonal wind components seem to be most important for the tidal modulations. In many cases the non-linear interaction between tides and planetary waves takes place in the stratosphere. (C) 2001 Elsevier Science Ltd. All rights reserved.