Relations Between Semidiurnal Tidal Variants Through Diagnosing the Zonal Wavenumber Using a Phase Differencing Technique Based on Two Ground-Based Detectors

Abstract

The winter upper atmosphere is associated with semidiurnal tidal variants, referring collectively to enhancements of near-12 h periodicities, including the lunar tide-like (M2) periodicity, solar semidiurnal (S2) spectral sidebands, and the quasi-semidiurnal westward propagating modes with zonal wavenumbers m = 1 and 3 (qSW1 and qSW3). Here we formulate a multipoint technique and implement the technique for a configuration of two midlatitude meteor radars, from Germany and China, to investigate the tidal variants. Statistical results illustrate that the 12 h periodicity is dominated consistently by the expected migrating mode (m = 2) between 2012 and 2016, consistent with the tidal climatology and in turn validating the technique. Our case study of 2013 sudden stratospheric warming reveals that the 11.6 h periodicity is characterized by m = 3, whereas the 12.4 h periodicity is dominated by m = 2 mode with a maximum amplitude 7.5 m/s and also comprises an additional mode m = 1 with a maximum amplitude 3.3 m/s. These observational evidences demonstrate, explicitly and for the first time, that (1) two independently reported categories of the variants, namely, the sidebands and the qSW1/qSW3 enhancements, are two different perspectives of identical phenomena, namely, the secondary waves of nonlinear interactions between SW2 and planetary waves, and (2) while M2 and the qSW1-associated secondary wave are entangled in the 12.4 h periodicity, M2 is superior to the sideband.