This project aims to investigate the causes and consequences of exceptionally cold and stable Arctic polar vortices and their associated ozone holes during winter/spring 2011 and 2020. The project will use the ICON (ICOsahedral Non-hydrostatic model) atmospheric model in conjunction with the ART module (Aerosols and Reactive Trace gases, Rieger et al. 2015) with different simulation setups (time-slice experiments, interactive and non-interactive stratospheric chemistry, with and without ozone-depleting substances (ODSs)). In addition, extensive use of complementary data is planned: CMIP6 model simulations, reanalysis data (ERA5 and MERRA) and GPS radio occultation observations (COSMIC, COSMIC-2a and CHAMP). The GPS observations will be used to estimate the amplitude of the gravity wave in the stratosphere prior and during winter/spring 2011 and 2020. In addition, the ICON-ART results and reanalysis data are separated into the balanced (Rossby) and and inertio-gravity (IG) circulations across many scales using the MODES software (Žagar et al, 2015). We hypothesize that either the anomalous injection of the upward propagating waves (both resolved Rossby waves and unresolved gravity waves) or the anomalous geometry of the polar vortex led to such anomalous ozone hole conditions during winter/spring 2011 and 2020. Additionally, we hypothesize that using interactive chemistry is essential to capture the full spectrum of the stratospheric variability, which is critical to capturing the downward influence of the stratospheric polar vortex on the troposphere.