The quasi-biennial oscillation (QBO), a ubiquitous feature of the zonal mean zonal winds in the equatorial lower stratosphere, is forced by selective dissipation of atmospheric waves that range in periods from days to hours. However, QBO circulations in numerical models tend to be weak compared with observations, probably because of limited vertical resolution that cannot adequately resolve gravity waves and the height range over which they dissipate. Observations are required to help quantify wave effects. The passage of a superpressure balloon (SPB) near a radiosonde launch site in the equatorial Western Pacific during the transition from the eastward to westward phase of the QBO at 20 km permits a coordinated study of the intrinsic frequencies and vertical structures of two inertia-gravity wave packets with periods near 1-day and 3 days, respectively. Both waves have large horizontal wavelengths of about 970 and 5500 km. The complementary nature of the observations provided information on their momentum fluxes and the evolution of the waves in the vertical. The near 1-day westward propagating wave has a critical level near 20 km, while the eastward propagating 3-day wave is able to propagate through to heights near 30 km before dissipation. Estimates of the forcing provided by the momentum flux convergence, taking into account the duration and scale of the forcing, suggests zonal force of about 0.3-0.4 m/s/day for the 1-day wave and about 0.4-0.6 m/s/day for the 3-day wave, which acts for several days.

Twenty six years of MF radar wind measurements made from 1994 to 2019 at Davis Station (68.6◦S, 77.9◦E) are used to study the mean re- sponse of the mesosphere-lower thermosphere to stratospheric warmings in the southern hemisphere. Warming events were detected using Modern- Era Retrospective Analysis for Research and Applications (MERRA)-2 data with a systematic search for reductions in the zonal-mean circulation at 60◦S and corresponding increases in polar temperatures. Some 38 events were identified, including the major warmings of 2002 and 2019, with an average of 1 to 2 warmings per year. At the 10 hPa level, the polar cap temperature increases ranged from 5 to 30 K, with a mean value of 11 K, while the zonal wind speed reductions varied between -7 to -43 ms−1, with −1 a mean value of -15 ms . Peak values occurred near 40 km. Warmings occurred mainly between August and October, with a small peak in oc- currence in April/May. The MF radar data showed an average reduction in the mesospheric eastward winds of about 5-7 ms−1 at heights near 75 km that occurred some 3-4 days prior to the changes in the stratosphere. Warming events were driven by episodic intensifications in planetary waves amplitudes, with quasi-stationary PW 1 being especially important. Plane- tary wave Eliassen-Palm flux divergences show a systematic behavior with time and height that is consistent with a poleward residual circulation and downwelling over the pole prior to the warming events and an equatorward flow and upwelling after the peak of the events.