Gravity waves and shear in the lower stratosphere: idealized experiments of baroclinic life cycles

Mixing plays a crucial role on redistributing radiation-actively trace species in the lower stratosphere. In particular, it is potentially the dominant effect for the formation of the extra-tropical transition layer (ExTL). However, various dynamical features can lead to mixing and the role of the small scale dynamics is not yet clear. In the extra-tropics, stratosphere troposphere exchange (STE) occurs frequently during baroclinic life cycles, e.g., in the vicinity of tropopause folds, cut-off lows, or stratospheric streamers. However, how the gravity waves (GWs) contributes to STE and mixing in the lower stratosphere is a research area with many open questions. A series of baroclinic life cycle experiments with the ICOsahedral Non-hydrostatic (ICON) general circulation model have been performed in order to study the impact of gravity waves on the transport and mixing between the upper troposphere and lower stratosphere (UTLS). Dry adiabatic experiments with varying horizontal and vertical resolution allowed to study the GW occurrence in relation to the model grid spacing. Moreover, the effect of varying initial conditions on the emergence of gravity waves is studied. We present analysis of the occurrence of GW in the various life cycles, their dependence on the model grid spacing and the initial conditions. Moreover, we present an analysis on the vertical shear of the horizontal wind associated with gravity waves and the potential for turbulence occurrence as a prerequisite for mixing. The focus of our analysis is the lowermost stratosphere and the effect of gravity wave induced mixing on the formation of the ExTL.