Observation and simulation of neutral air density in the middle atmosphere during the 2021 sudden stratospheric warming event

Abstract. Sudden stratospheric warmings (SSWs) are dramatic events in the polar winter stratosphere that are accompanied by atmospheric parameter anomalies in the stratosphere and mesosphere. Microwave Limb Sounder and Global Navigation Satellite System Occultation Sounder observations on board the Chinese FengYun 3 satellites indicate a rapid increase of over 50 % in the mesospheric density at high latitudes around the onset date during the 2021 major SSW event. The amplification of the zonal mean density around the onset is proportional to the latitude increase with a maximum increment of 83.3 % at 59 km above 80° N, which is more than 3 times larger than the climatological standard deviation (23.1 %). 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 reproduces the global circulation 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. Obvious density disturbances in the upper stratosphere and mesosphere were observed by the lidar deployed in Beijing (40.3° N, 116.2° E).