Impact of QBO and ENSO on the summer polar mesospheric water vapor

Both quasi-biennial oscillation (QBO) and El Niño-Southern Oscillation (ENSO) can strongly influence the stratosphere temperature, wind, and general circulation (e.g. Brewer-Dobson circulation) as well as tracer gases (e.g. ozone). However, their influence in the mesosphere, especially summer polar mesosphere, is still not fully understood. In this study, we investigate the influence of QBO and ENSO on the summer polar mesospheric water vapor. Analyses use the observed satellite temperature and water vapor datasets from the Microwave Limb Sounder (MLS) between 2004 and 2018, simulations from the Whole Atmospheric Community Climate Model version 4 (WACCM4) between 1956 and 2015, and the European Centre for Medium-Range Weather Forecasting (ECMWF) Reanalysis (ERA-Interim) between 1979 and 2018. We find that both QBO and ENSO can strongly modulate the southern hemisphere (SH) high latitude stratosphere zonal wind in November, and cause anomalous gravity wave (GW) filtering and thus GW forcing in the SH polar mesosphere. During QBO easterly phases and El Niño events in November, the anomalous increases of GW forcing in the SH mesosphere enhances the upwelling and cooling in the summer polar region, which can increase the SH summer polar mesospheric water vapor via transporting water vapor rich air from lower altitudes to higher altitudes. This further indicates that the QBO and ENSO can likely play an important role in influencing the SH summer polar mesospheric clouds by modulating both polar mesospheric temperature and water vapor.