Emulating lateral gravity wave propagation in a global chemistry–climate model (EMAC v2.55.2) through horizontal flux redistribution
<p>The columnar approach of gravity wave (GW) parameterisations in weather and climate models has been identified as a potential reason for dynamical biases in middle-atmospheric dynamics. For example, GW momentum flux (GWMF) discrepancies between models and observations at 60<span class=&q...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-10-01
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| Series: | Geoscientific Model Development |
| Online Access: | https://gmd.copernicus.org/articles/16/5561/2023/gmd-16-5561-2023.pdf |
| Summary: | <p>The columnar approach of gravity wave (GW) parameterisations in weather and climate models
has been identified as a potential reason for dynamical biases in middle-atmospheric dynamics.
For example, GW momentum flux (GWMF) discrepancies between models and observations at 60<span class="inline-formula"><sup>∘</sup></span> S arising
through the lack of horizontal orographic GW propagation are suspected to cause deficiencies
in representing the Antarctic polar vortex.
However, due to the decomposition of the model domains onto different computing tasks for
parallelisation, communication between horizontal grid boxes is computationally extremely
expensive, making horizontal propagation of GWs unfeasible for global chemistry–climate simulations.</p>
<p>To overcome this issue, we present a simplified solution to approximate horizontal
GW propagation through redistribution of the GWMF at one single
altitude by means of tailor-made redistribution maps.
To generate the global redistribution maps averaged for each grid box, we use a
parameterisation describing orography as a set of mountain ridges with
specified location, orientation and height combined with a
ray-tracing model describing lateral propagation of so-generated mountain waves.
In the global chemistry–climate model (CCM) EMAC (ECHAM MESSy Atmospheric Chemistry),
these maps then allow us to redistribute the GW momentum
flux horizontally at one level, obtaining an affordable overhead of computing resources.
The results of our simulations show GWMF and drag patterns that are horizontally
more spread out than with the purely columnar approach;
GWs are now also present above the ocean and regions without mountains.
In this paper, we provide a detailed description of how the redistribution maps
are computed and how the GWMF redistribution is implemented in the CCM.
Moreover, an analysis shows why 15 km is the ideal altitude for the redistribution.
First results with the redistributed orographic GWMF provide clear evidence that
the redistributed GW drag in the Southern Hemisphere has the potential to modify and improve
Antarctic polar vortex dynamics, thereby paving
the way for enhanced credibility of CCM simulations and projections of polar stratospheric ozone.</p> |
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| ISSN: | 1991-959X 1991-9603 |