Quantification of heat and constituent transport by gravity waves (GWs) in global models is challenging due to limited model resolutions. Current parameterization schemes suffer from oversimplification and often underestimate the transport rate. In this study, a new approach is explored to quantify the effective vertical eddy diffusion by using a high‐resolution Whole Atmosphere Community Climate Model (WACCM) simulation based on scale invariance. The WACCM simulation can partially resolve the mesoscale GW spectrum down to 250 km horizontal wavelength, and the heat flux and the effective vertical eddy diffusion by these waves are calculated directly. The effective vertical diffusion by the smaller‐scale, unresolved waves, is then deduced based on scale invariance, following the method outlined by H.‐L. Liu (2019) in quantifying GW momentum flux and forcing. The effective vertical diffusion obtained is generally larger than that obtained from parameterizations, and is comparable with that derived from observations in the mesosphere and lower thermosphere region.
The paper presents results of simulations with a high‐resolution (equivalent to ∼67‐km grid size) Martian general circulation model (MGCM) from the surface up to the mesosphere for a full Martian year. The obtained climatology of the small‐scale disturbances can serve as a proxy for gravity waves (GWs) that are largely not resolved by MGCMs with conventional grid resolution and thus have to be parameterized. GW activity varies greatly with season and geographical location, which contradicts with the constant in space and time sources in the lower atmosphere adopted by GW parameterizations employed by coarse‐grid MGCMs. In particular, lower‐atmospheric GW activity is smaller in polar regions of the troposphere throughout all seasons, and the intensity is larger in southern spring and summer and in winter hemisphere at both solstices. In the mesosphere, the peak of GW activity shifts toward middle and high latitudes, and the interhemispheric symmetry is much larger compared to the lower atmosphere. The detailed climatology created in this study can be used for prescribing sources of GWs in parameterizations utilized by MGCMs as well as for validating the parameterizations in the middle and upper atmosphere.
more » « less- NSF-PAR ID:
- 10453138
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Planets
- Volume:
- 124
- Issue:
- 6
- ISSN:
- 2169-9097
- Page Range / eLocation ID:
- p. 1618-1632
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Long‐term efforts have sought to extend global model resolution to smaller scales enabling more accurate descriptions of gravity wave (GW) sources and responses, given their major roles in coupling and variability throughout the atmosphere. Such studies reveal significant improvements accompanying increasing resolution, but no guidance on what is sufficient to approximate reality. We take the opposite approach, using a finite‐volume model solving the Navier‐Stokes equations exactly. The reference simulation addresses mountain wave (MW) generation and responses over the Southern Andes described using isotropic 500 m, central resolution by Fritts et al. (2021),
https://doi.org/10.1175/JAS-D-20-0207.1 and Lund et al. (2020),https://doi.org/10.1175/JAS-D-19-0356.1 . Reductions of horizontal resolution to 1 and 2 km result in (a) systematic increases in initial MW breaking altitudes, (b) weaker, larger‐scale generation of secondary GWs and acoustic waves accompanying these dynamics, and (c) significantly weaker and less extended responses in the mesosphere in latitude and longitude. Horizontal resolution of 4 km largely suppresses instabilities, but allows weak, sustained mean‐flow interactions. Responses for 8 km resolution are very weak and fail to capture any aspects of the high‐resolution responses. The chosen mean winds allow efficient MW penetration into the mesosphere and lower thermosphere, hence only exhibit strong pseudo‐momentum deposition and mean wind decelerations at higher altitudes. A companion paper by Fritts et al. (2022),https://doi.org/10.1029/2021JD036035 explores the impacts of decreasing resolution on responses in the thermosphere. -
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Abstract Four state-of-the-science numerical weather prediction (NWP) models were used to perform mountain wave (MW)-resolving hindcasts over the Drake Passage of a 10-day period in 2010 with numerous observed MW cases. The Integrated Forecast System (IFS) and the Icosahedral Nonhydrostatic (ICON) model were run at Δ
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