The Neutral Air Density revolutions in the Middle Atmosphere During 2021 SSW

The sudden stratospheric warming (SSW) is dramatic event in the winter stratosphere, during which the stratospheric temperature rapidly increases and the zonal winds reverse over the Poles. The variation of the neutral air density in the middle atmosphere during the 2021 major SSW event is investigated, using the observations from Microwave Limb Sounder (MLS), the Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) on board the Chinese FengYun 3 (FY-3) and lidar deployed in Beijing (40.3 N, 116.2 E). A rapid increase of over 50% is observed by the satellites in the mesospheric density at high latitudes around the onset date and obvious density disturbances in the upper stratosphere and mesosphere were observed by lidar deployed in Beijing (40.3 N, 116.2 E). The amplification of the zonal mean density around the onset is proportional to the latitude increase with a maximum increment above 80 N, which is more than three times larger than the climatological standard deviation. The horizontal density distributions are influenced by the changing polar vortex fields. A simulation using a specified dynamics version of the Whole Atmosphere Community Climate Model is consistent overall with the observations and presents a severe change in the planetary wave forcing and residual meridional circulation mass flux followed by a change in the density tendency. These results demonstrate that the observed enhanced density is primarily attributed to the altered planetary waves and residual circulation during the SSW event. The observations and simulations also indicate that the density anomalies could extend to middle latitudes and lead the density disturbances over Beijing.