The Climatology of Elevated Stratopause Events in the UA-ICON Model and the Contribution of Gravity Waves
Abstrakt
The climatologies of the stratopause height and temperature in the UA-ICON model are examined by comparing them to 17-years (2005-2021) of Microwave Limb Sounder (MLS) observations. In addition, the elevated stratopause (ES) event occurrence, their main characteristics, and driving mechanisms in the UA-ICON model are examined using three 30-year time-slice experiments.
While UA-ICON reasonably simulates the large-scale stratopause properties similar to MLS observations, at polar latitudes in the Southern Hemisphere the stratopause is similar to 8 K warmer and similar to 3 km higher than observed. A time lag of about two months also exists in the occurrence of the tropical semiannual oscillation of the stratopause compared to the observations.
ES events occur in similar to 20% of the boreal winters, after major sudden stratospheric warmings (SSWs). Compared to the SSWs not followed by ES events (SSW-only), the ES events are associated with the persistent tropospheric forcing and prolonged anomalies of the stratospheric jet.
Our modeling results suggest that the contributions of both gravity waves (GW)s and resolved waves are important in explaining the enhanced residual circulation following ES events compared to the SSW-only events but their contributions vary through the lifetime of ES events. We emphasize the role of the resolved wave drag in the ES formation as in the sensitivity test when the non-orographic GW drag is absent, the anomalously enhanced resolved wave forcing in the mesosphere gives rise to the formation of the elevated stratopause at about 85 km.