The 16-Day Planetary Wave Triggers the SW1-Tidal-Like Signatures During 2009 Sudden Stratospheric Warming

Abstract

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 ∼12.4 and ∼11.6 hr, were detected at low-frequency resolutions and misinterpreted as SW1 and SW3, respectively. While He et al. (2018, https://doi.org/10.1002/2018JD028400) associated the 11.6-hr oscillation conclusively to the SW3-like signature during SSW 2013 by diagnosing its wave number, the SW1-like 12.4hr 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.