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The dynamical characteristics of the zonal wavenumber 1 (s = 1) Rossby-gravity (RG) wave are examined using recently available reanalysis data for the whole neutral atmosphere over 16 years. An isolated peak is detected in the two-dimensional zonal wavenumber-frequency spectra that likely corresponds to the theoretically-expected s = 1 RG mode at heights of z = 30, 50, 65, and 80 km. The wave period of the spectral peak is approximately 1.3 days, which is close to one day. The s = 1 RG wave is successfully extracted using a band-pass filter after removing the diurnal tide with quite large amplitudes. The s = 1 RG wave exhibits a characteristic seasonal variation: the geopotential height (GPH) amplitudes are largest in the winter hemisphere in the stratosphere and lower mesosphere while enhancement is observed in both the winter and summer hemispheres in the upper mesosphere. Phase structures are examined in detail for a strong case. The horizontal phase structure at each height is consistent with the normal mode theory. The vertical phase structure is approximately barotropic from the lower stratosphere to the upper mesosphere at 30°N and 30°S where the amplitudes are large. [ABSTRACT FROM AUTHOR]

Mesospheric winds from two longitudinal sectors at 53°N latitude are combined to investigate quasi‐two‐day waves (Q2DWs) and their nonlinear interactions with tides. In a summer 2019 case study, we diagnose the zonal wavenumber m of spectral peaks at expected frequencies through two dual‐station approaches, a phase differencing technique (PDT) on individual spectral peaks and a least squares procedure on family batched peaks. Consistent results from the approaches verify the occurrences of Rossby‐gravity modes (m = 3 and 4 at periods T = 2.1 and 1.7 days), and their secondary waves (SWs) generated from interactions with diurnal, semi‐diurnal, ter‐diurnal, and quatra‐diurnal migrating tides. We further extend the PDT to 2012–2019, illustrating that Q2DWs exhibit significant interannual variability. Composite analysis reveals seasonal and altitude variations of the Rossby‐gravity modes and their SWs. The Rossby‐gravity modes maximize in local summer, whereas their 16‐ and 9.6‐h SWs appear more in winter. Plain Language Summary: The quasi‐two‐day wave is the strongest and most widely studied planetary wave occurring in the mesosphere. Existing observational analyses are based on either single‐satellite or ‐station approaches, which suffer from temporal and spatial aliasing, respectively. The current study implements and develops dual‐station approaches to investigate the mesospheric quasi‐two‐day wave at 53°N latitude, in a case and a statistical study. Our approaches allow diagnosing both the frequency and zonal wavenumber. In the case study, we diagnosed two Rossby‐gravity modes and the secondary waves (SWs) of the nonlinear interactions between the Rossby‐gravity modes and the migrating tides at periods of 24, 12, 8, and 6 h. While the interactions with the 24‐ and 12‐h tides are expected, those with the 8‐ and 6‐h tides are reported for the first time. In the statistical study, we report the seasonality and altitude variation of the Rossby‐gravity modes and their most dominant SWs. Key Points: Multi‐station approaches are developed and applied to diagnose zonal wavenumber m of near‐2‐day, ‐16‐h, ‐9.6‐h, and ‐6.9‐h spectral peaksDiagnosed are Rossby‐gravity modes with m = 3 and 4, and their secondary waves from nonlinear interactions with 24‐, 12‐, 8‐, and 6‐h migrating tidesSeasonally, the most dominant near‐2‐day, ‐16‐h, ‐9.6‐h waves occur in summer, winter, and winter, respectively [ABSTRACT FROM AUTHOR]