Non-linear interaction of the quasi 2-day wave and longterm oscillations in the summer midlatitude mesopause region as seen from LF D1 wind measurements over Central Europe (Collm, 52°N, 15°E)

From night-time mesopause region wind measurements over Central Europe, the day-to-day variability of the measured quasi 2-day wave is investigated with respect to its correlation with summer planetary wave events. A 14-year dataset of summer winds is used. The results indicate that the 2-day wave is modulated by planetary waves, especially by the 16-day wave. Secondary frequencies that are expected, if a non-linear interaction between the waves is assumed, are found from regression analysis. Additionally, these secondary oscillations are modulated by the duration of the quasi 2-day wave event itself. Tertiary frequencies that belong to; this modulation are also found from periodogram analysis. The long-term dataset analysis shows that the non-linear interaction is a regular phenomenon that is frequently found in connection with planetary wave activity in the summer upper mesosphere and lower thermosphere. (C) 1998 Elsevier Science Ltd. All rights reserved.