Structure of the quasi-2-day wave (Q2DW) in the mesosphere and lower thermosphere (MLT) was compared between the northern and southern hemispheres, employing temperature and geopotential height data obtained from the Microwave Limb Sounder (MLS) onboard NASA’s Earth Observing System (EOS) Aura satellite. The Q2DW in horizontal winds was derived using balance equations with MLS geopotential height data. Amplitudes were maximized at ~40° in summer with larger amplitudes in the meridional wind than the zonal wind in both hemispheres, but with much larger amplitudes in the southern hemisphere and a longer duration of enhancements in the northern hemisphere. Weaker enhancements were exhibited in winter in both hemispheres, but maximized at higher latitudes only in the southern hemisphere meridional component. Responses were moderately enhanced from late April to early May only in the southern hemisphere. The westward propagating zonal wavenumber 3 (W3) was largest in summer in both hemispheres, but the Q2DW comprised superposition with other modes in winter. Eliassen-Palm fluxes were derived for each mode. In the southern hemisphere, W3, W2, and W1 in January exhibited upward fluxes at lower latitudes, poleward fluxes at lower altitudes and equatorward fluxes at higher altitudes. A W3 mode in July in the northern hemisphere, on the other hand, exhibited upward and poleward fluxes in the entire altitude range. The Q2DW balance winds were compared with the radar winds. They agreed reasonably in amplitude and phase in summer in the southern hemisphere and lower latitudes in summer in the northern hemisphere and in winter hemispheres.

The polar summer mesosphere is the Earthâ\euro™s coldest region, allowing the formation of mesospheric ice clouds. These ice clouds produce strong polar mesospheric summer echoes (PMSE) that are used as tracers of mesospheric dynamics. Here we report the first observations of extreme vertical drafts ($\pm$50 ms$^{-1}$) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles a solitary wave in a varicose mode, narrow along propagation (3–4 km) and elongated ($>10$ km) transverse to propagation direction, with a relatively large vertical extent ($\sim$13 km). These spatial features are similar to previously observed mesospheric bores, but we observe only one crest with much larger vertical extent and higher vertical velocities.

Mesospheric winds from three longitudinal sectors at about 65$^\circ$N and 54$^\circ$N latitude are combined to diagnose the zonal wavenumbers ($m$) of high-frequency-resolved spectral wave signatures during the rare southern hemisphere sudden stratospheric warming (SSW) of 2019. Diagnosed are quasi-10- and 6-day planetary waves (Q10DW and Q6DW, $m$=1), solar semi-diurnal tides with $m$=1, 2, 3 (SW1, SW2, and SW3), lunar semi-diurnal tide, and the upper and lower sidebands (USB and LSB, $m$=1 and 3) of Q10DW-SW2 nonlinear interaction. We further present a 7-year composite analysis to distinguish SSW effects from climatological behaviors. Immediately before (after) the SSW onset, LSB (USB) enhances, accompanied by the enhancing (fading) Q10DW, and a weakening of climatological SW2 maximum. These behaviors are explained in terms of Manley-Rowe energy relation, i.e., the energy goes first from SW2 to Q10DW and LSB, and then from SW2 and Q10DW to USB.

The polar summer mesosphere is the Earth’s coldest region, allowing the formation of mesospheric ice clouds. These clouds produce strong polar mesospheric summer echoes (PMSE) that are used as tracers of mesospheric dynamics. Here we report the first observations of extreme vertical drafts (±50~m/s) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles mesospheric bores, i.e., narrow along propagation (3–4~km) and elongated (>10~km) transverse to propagation direction. Additionally, our event presents a large vertical extent (± 3–4~km), resembling a “super bore”. Powerful vertical drafts, intermittent in space and time, emerge also in direct numerical simulations of stratified flows, predicting non-Gaussian statistics of vertical velocities. This evidence suggests that our event, and perhaps previous bores, might result from the interplay of gravity waves and turbulent motions.