Project B06:
Impact of small-scale dynamics on UTLS transport and mixing

Brief Summary

Zonal-mean tracer transport through the UTLS is characterized by the mean residual Brewer-Dobson circulation (BDC) and it is modified by mixing due to turbulence and partly gravity waves (GWs). Both GWs and turbulence occur on scales which require to be parameterized in weather and climate models. However, available parameterizations fail to reliably describe the effects on tracers. With the overall goal of mending this situation we want to pursue the following core objectives:

1. We will further improve the newly developed GW model MS-GWaM in ICON to address the effects on tracers of the BDC, via corresponding diagnostics, and mixing, through passive-tracer simulations. In particular, we will focus on the description of the spontaneous-imbalance source, which is of major importance in the extratropical UTLS.
2. The direct coupling of MS-GWaM to tracers will be addressed systematically through idealized investigations. This will allow us to further improve the description of this coupling in ICON/MS-GWaM and to study the consequences with regard to UTLS tracer transport.
3. Current turbulence parameterizations do not take into account the complex nature of turbulence (non-homogeneous, anisotropic, non-Kolmogorov, patchy, and three-dimensional) in the strongly stratified UTLS. We therefore improve the corresponding approach in ICON using large-eddy simulations (LES) to quantify the transport and mixing in the UTLS and investigate the contribution of turbulent mixing in the UTLS.
4. We will validate Objectives 1. – 3. by using suitable observations and wave-resolving simulations. For this purpose we will analyze high-resolution airborne measurements for GW properties and GW occurrence frequency. This will be supplemented by GW resolving ICON simulations of baroclinic life cycles, the ensuing spontaneous GW emission and related tracer effects.

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