Amplitude modulation of the semidiurnal tide based on MLT wind measurements with a European/Siberian meteor radar network in October – December 2017

Abstract

We present results on temporal and longitudinal modulations of semidiurnal tide amplitudes in the mesosphere and lower thermosphere winds. The wind data were obtained during October – December 2017 when six meteor radars operated simultaneously. The radar network covers latitudes from 51°N to 72°N and longitudes from 13°E to 178°E. The results show a clear tidal 8–9 day amplitude modulation, which significantly changes with latitude. Evidence is provided for a non-linear interaction between the semidiurnal tide and eastward and westward propagating planetary waves as a source of the modulation. The modulation from the interaction with eastward propagating waves of zonal wavenumber 1 is observed at high latitudes (65°–72°N). A modulation in correspondence with non-linear interaction with a westward propagating wave of zonal wavenumber 1 replaces the first one at middle latitudes (51°–52°N). Furthermore, we found a significant statistical link between the upper stratosphere zonal jet oscillations and the longitudinal difference in tidal amplitudes obtained at the Collm and Angarsk mid-latitude stations. The correlation coefficients are about 0.61 and 0.55 for zonal and meridional amplitudes, respectively. The difference between tidal winds taken at different longitudes grows in amplitude for both wind components at middle latitudes during the increase of stationary planetary wave 1 activity in December. TIDI upper mesospheric wind data indicate a semidiurnal westward propagating tide with wavenumber 3 as the leading source of this effect. The difference between tidal winds at high-latitudes shows different behaviour for the zonal and meridional wind components in December.