Lowering of Tropopause and Strengthening of Tropopause Inversion Layer at Antarctica During the 2002 and 2019 Southern Sudden Stratospheric Warming Events as Seen by Radiosonde Observations and ERA5 Reanalysis

Using radiosonde and ERA5 reanalysis data, we investigated the spatial and temporal variations in the tropopause and tropopause inversion layer (TIL) in the Antarctic region during the 2002 and 2019 southern sudden stratospheric warming (SSW) events and the mechanism involved. Following these SSW events there was a sharper TIL and a warmer and lower tropopause. After the onset of rapid warming during the major SSW event in 2002 and the minor SSW event in 2019, the magnitudes of these anomalies increased and reached their respective first peaks. The anomalies increased and peaked again following the early final breakdown of the polar vortex (i.e., the switch to summer circulation). During the SSW events and final breakdown of the polar vortex in 2002 and 2019, stratospheric residual mean circulation, which was driven by planetary waves, was the primary cause of these anomalies. The adiabatic heating of the anomalous downwelling residual mean circulation above the tropopause led to a decrease in the tropopause height and a warming of the tropopause temperature. It also led to increased static stability near the tropopause by dynamical heating, which represented a strengthened TIL. In addition, approximately 4% and 1.9% of the strengthening of the TIL in 2002 and 2019, respectively, can be attributed to the increased anticyclonic circulation at the tropopause.