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. Observational evidence of a quasi-quadrennial oscillation (QQO) in the polarmesosphere is presented based on the analysis of 24 years of hydroxyl (OH)nightglow rotational temperatures derived from scanning spectrometerobservations above Davis research station, Antarctica (68 ∘  S,78 ∘ E). After removal of the long-term trend and solar cycle response,the residual winter mean temperature variability contains an oscillationover an approximately 3.5–4.5-year cycle with a peak-to-peak amplitude of3–4 K. Here we investigate this QQO feature in the context of the global temperature, pressure, wind, and surfacefields using satellite, meteorological reanalysis, sea surface temperature, and sea ice concentration data setsin order to understand possible drivers of the signal. Specifically, correlation and composite analyses are madewith data sets from the Microwave Limb Sounder on the Aura satellite (Aura/MLS v4.2) and the Sounding of the Atmosphereusing Broadband Emission Radiometry instrument on the Thermosphere Ionosphere Mesosphere EnergeticsDynamics satellite (TIMED/SABER v2.0), ERA5 reanalysis, the Extended Reconstructed Sea SurfaceTemperature (ERSST v5), and Optimum-Interpolation (OI v2) sea ice concentration. We find a significant anti-correlation between theQQO temperature and the meridional wind at 86 km altitude measured by amedium-frequency spaced antenna radar at Davis ( R2∼0.516 ; poleward flow associated with warmer temperatures at ∼ 0.83 ± 0.21  K (ms −1 ) −1 ). The QQO signal is also marginally correlatedwith vertical transport as determined from an evaluation of carbon monoxide(CO) concentrations in the mesosphere (sensitivity 0.73±0.45  K ppmv −1 CO, R2∼0.18 ). Together this relationship suggests that the QQO isplausibly linked to adiabatic heating and cooling driven by the meridionalflow. The presence of quasi-stationary or persistent patterns in the ERA5data geopotential anomaly and the meridional wind anomaly data during warmand cold phases of the QQO is consistent with tidal or planetary wavesinfluencing its formation, which may act on the filtering of gravity wavesto drive an adiabatic response in the mesosphere. The QQO signal plausiblyarises from an ocean–atmosphere response, and appears to have a signature inAntarctic sea ice extent.

atmospheric chemistry and physics

Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 2: Evidence of a quasi-quadrennial oscillation (QQO) in the polar mesosphere