Interactions between Mesoscale and Submesoscale Gravity Waves and Their Efficient Representation in Mesoscale-Resolving Models
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jas-d-17-0289.1.pdf
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Checksum (MD5)
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Author(s)
Wilhelm, Jannik
Bölöni, Gergely
Wei, Junhong
Ribstein, Bruno
Klein, Rupert
Achatz, Ulrich
Akylas, Triantaphyllos R
Date Issued
January 2018
Journal
Journal of the Atmospheric Sciences
Publisher
American Meteorological Society
Citation
Wilhelm, Jannik et al. “Interactions Between Mesoscale and Submesoscale Gravity Waves and Their Efficient Representation in Mesoscale-Resolving Models.” Journal of the Atmospheric Sciences 75, 7 (July 2018): 2257–2280 © 2018 American Meteorological Society
Version
Final published version
Abstract
As present weather forecast codes and increasingly many atmospheric climate models resolve at least part of the mesoscale flow, and hence also internal gravity waves (GWs), it is natural to ask whether even in such configurations subgrid-scale GWs might impact the resolved flow and how their effect could be taken into account. This motivates a theoretical and numerical investigation of the interactions between unresolved submesoscale and resolved mesoscale GWs, using Boussinesq dynamics for simplicity. By scaling arguments, first a subset of submesoscale GWs that can indeed influence the dynamics of mesoscale GWs is identified. Therein, hydrostatic GWs with wavelengths corresponding to the largest unresolved scales of present-day limited-area weather forecast models are an interesting example. A large-amplitude WKB theory, allowing for a mesoscale unbalanced flow, is then formulated, based on multiscale asymptotic analysis utilizing a proper scale-separation parameter. Purely vertical propagation of submesoscale GWs is found to be most important, implying inter alia that the resolved flow is only affected by the vertical flux convergence of submesoscale horizontal momentum at leading order. In turn, submesoscale GWs are refracted by mesoscale vertical wind shear while conserving their wave-action density. An efficient numerical implementation of the theory uses a phase-space ray tracer, thus handling the frequent appearance of caustics. The WKB approach and its numerical implementation are validated successfully against submesoscale-resolving simulations of the resonant radiation of mesoscale inertia GWs by a horizontally as well as vertically confined submesoscale GW packet. Keywords: Dynamics; Gravity waves; Internal waves; Subgrid-scale processes; Resonance; Parameterization
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
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DOI of Published Version
https://doi.org/10.1175/JAS-D-17-0289.1
