Abstract
Abstract. Polar stratospheric clouds (PSCs) are a driver for ozone depletion in the lower polar stratosphere. They provide surface for heterogeneous reactions activating chlorine and bromine reservoir species during the polar night. The large-scale effects of PSCs are represented by means of parameterisations in current global chemistry–climate models, but one process is still a challenge: the representation of PSCs formed locally in conjunction with unresolved mountain waves. In this study, we investigate direct simulations of PSCs formed by mountain waves with the ICOsahedral Nonhydrostatic modelling framework (ICON) with its extension for Aerosols and Reactive Trace gases (ART) including local grid refinements (nesting) with two-way interaction. Here, the nesting is set up around the Antarctic Peninsula, which is a well-known hot spot for the generation of mountain waves in the Southern Hemisphere. We compare our model results with satellite measurements of PSCs from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and gravity wave observations of the Atmospheric Infrared Sounder (AIRS). For a mountain wave event from 19 to 29 July 2008 we find similar structures of PSCs as well as a fairly realistic development of the mountain wave between the satellite data and the ICON-ART simulations in the Antarctic Peninsula nest. We compare a global simulation without nesting with the nested configuration to show the benefits of adding the nesting. Although the mountain waves cannot be resolved explicitly at the global resolution used (about 160 km), their effect from the nested regions (about 80 and 40 km) on the global domain is represented. Thus, we show in this study that the ICON-ART model has the potential to bridge the gap between directly resolved mountain-wave-induced PSCs and their representation and effect on chemistry at coarse global resolutions.
Highlights
Polar stratospheric clouds (PSCs) play a key role in explaining the rapid ozone loss in the polar stratosphere during local spring (e.g. Solomon et al, 1986; Solomon, 1999; Braesicke et al, 2018)
It was impossible to directly simulate mountain-wave-induced PSCs in global chemistry models due to the coarse resolution in that kind of simulations. We investigated this problem with the scheme for PSCs in the ICOsahedral Non-hydrostatic modelling framework with its extension for Aerosols and Reactive Trace gases (ICON-ART)
The scheme forms ice PSCs based on the microphysics of the meteorological model, liquid particles by the analytic expression of Carslaw et al (1995) with some improvements with respect to the constant particle number concentration and nitric acid trihydrate particles (NAT) particles by a kinetic non-equilibrium approach with a flexibly selectable size distribution
Summary
Polar stratospheric clouds (PSCs) play a key role in explaining the rapid ozone loss in the polar stratosphere during local spring (e.g. Solomon et al, 1986; Solomon, 1999; Braesicke et al, 2018). We apply the two-way nesting at the Antarctic Peninsula with a resolution of 40 km in the grid refinement This resolution still misses directly resolving gravity waves with horizontal wavelengths lower than about 300 km (cf Geller et al, 2013), but we chose this configuration (1) for a balance between accuracy and computational expense and (2) to show how CCMs could already benefit from modest higher resolutions. We selected the Antarctic Peninsula for this study with the ICON-ART model because it is a well-known hot spot of mountain-wave-induced PSCs (Bacmeister, 1993; Bacmeister et al, 1994; McDonald et al, 2009; Alexander et al, 2011; Hoffmann et al, 2017). 3, the simulation set-up is pointed out that is used to examine the mountain wave event at the Antarctic Peninsula This is followed by a description of the AIRS and CALIOP instruments in Sect.
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