Nonlinear Interactions of Planetary-Scale Waves in Mesospheric Winds Observed at 52°N Latitude and Two Longitudes

Abstract

Nine-years of mesospheric wind measurements, from two meteor radars at 52°N latitude, were analyzed to study planetary waves (PWs) and tides through estimating their zonal wavenumbers. The analysis reveals that multi-day oscillations are predominantly driven by PW normal modes (NMs), which exhibit distinct seasonal variations and statistical association with Sudden Stratospheric Warming events. Specifically, a prominent 6-day NM emerges in April, followed by dominant 4- and 2-day NMs persisting until June, with subsequent peaks of 2-, 4-, and 6-day NMs extending from July to October. Furthermore, this study presents the first observational verification of the frequencies and zonal wavenumbers of over 10 secondary waves, arising from nonlinear interactions among planetary-scale waves. A notable finding is the prevalence of non-migrating components in the winter 24-hr and summer 8-hr tides, phenomena attributed to the nonlinear interactions. Our findings highlight the complexity of atmospheric nonlinear dynamics in generating diverse planetary-scale periodic oscillations.