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Enhanced nonmigrating tides SW1 (SWx represents semidiurnal westward mode with zonal wave number x) and SW3 during sudden stratospheric warming (SSW) were traditionally attributed to nonlinear interactions of quasi-stationary planetary waves with the migrating tide SW2. Recent studies specified hypothetically that responsible for the interactions is the 16-day wave, instead of the broadly accepted quasi-stationary planetary waves. It is suspected that the 16-day-wave-triggered secondary waves, at periods similar to 12.4 and similar to 11.6 hr, were detected at low-frequency resolutions and misinterpreted as SW1 and SW3, respectively. While He et al. (2018, ) associated the 11.6-hr oscillation conclusively to the SW3-like signature during SSW 2013 by diagnosing its wave number, the SW1-like 12.4 hr wave, however, has never been explicitly resolved, given its proximity to the period of an active lunar tide. Here, using the coherency in the mesospheric wind between two longitudinal sectors during SSW 2009, we identify a 12.4-hr oscillation dominated by wave number 1 and therefore associate it to the SW1-like signature.

Plain Language Summary The winter upper atmosphere is populated by global-scale oscillations among which the most radical one appears nearby the period of 12 hr. The existing studies suggest that the near-12-hr oscillation consists of at least six waves, namely, the migrating lunar and solar tides, two nonmigrating tides, and two secondary waves of the nonlinear interactions between the migrating solar tide and traveling planetary waves. The current work, together with a counterpart work (He et al., 2018), disentangles the near-12-hr oscillation into high-frequency-resolved isolated spectral peaks and investigates the longitudinal variation in the phase of the isolated peaks through jointly studying the mesospheric wind collected by longitudinally separated radars in early 2009 and early 2013. Results suggest that the nonmigrating tides did not enhance in both cases and demonstrate that the occurrence of secondary waves might have been misinterpreted as the nonmigrating tides in studies at low-frequency resolutions.