Climate impact of clear air turbulence induced mixing in the UTLS

Abstract

<p>The upper troposphere / lower stratosphere (UTLS) region has been identified as a region with a high climate sensitivity of the Earth's atmosphere. Past studies have shown that mixing processes can have a substantial impact on the radiative budget of the atmosphere with implications for the climate of the planet. However, in most large-scale models some of these mixing processes are hardly resolved or considered explicitely.<br>In this study, we focus on clear air turbulence (CAT) as a dynamically driven mixing process, which can induce vertical mixing of radiative active trace gases. For this purpose, we have equipped a chemistry-climate model with a diagnostics for dynamical CAT including vertical stability conditions and a mixing parameterisation for CAT-induced vertical exchange of trace gases.  <br>With the help of this tool we analyse the occurrence of CAT, the mixing of chemical compounds and the resulting radiative impact of this mixing.<br>The model simulations indicate a more efficient mixing of trace species in the UTLS, weakening some of the strong gradients of compounds, such that an occasional deeper penetration into the lower stratosphere becomes possible.<br>A suitable choice of simulation configuration also allows us to disentangle the radiative forcing of climate active gases (e.g., N<sub>2</sub>O, O<sub>3</sub>, CH<sub>4</sub>) from<br>feedback processes occurring in the holistic system. </p>