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Gravity Wave Dynamics in a Mesospheric Inversion Layer: 2. Instabilities, Turbulence, Fluxes, and Mixing
Author(s) -
Fritts David C.,
Wang Ling,
Laughman Brian,
Lund Thomas S.,
Collins Richard L.
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2017jd027442
Subject(s) - physics , instability , turbulence , mechanics , dissipation , turbulence kinetic energy , adiabatic process , k omega turbulence model , k epsilon turbulence model , atmospheric sciences , computational physics , thermodynamics
A companion paper by Fritts, Laughman, et al. (2017) employed an anelastic numerical model to explore the dynamics of gravity waves (GWs) encountering a mesospheric inversion layer (MIL) having a moderate static stability enhancement and a layer of weaker static stability above. That study revealed that MIL responses, including GW transmission, reflection, and instabilities, are sensitive functions of GW parameters. This paper expands on two of the Fritts, Laughman, et al. (2017) simulations to examine GW instability dynamics and turbulence in the MIL; forcing of the mean wind and stability environments by GW, instability, and turbulence fluxes; and associated heat and momentum transports. These direct numerical simulations resolve turbulence inertial‐range scales and yield the following results: GW breaking and turbulence in the MIL occur below where they would otherwise, due to enhancements of GW amplitudes and shears in the MIL. 2‐D GW and instability heat and momentum fluxes are ~20–30 times larger than 3‐D instability and turbulence fluxes. Mean fields are driven largely by 2‐D GW and instability dynamics rather than 3‐D instabilities and turbulence. 2‐D and 3‐D heat fluxes in regions of strong turbulence yield small departures from initial T ( z ) and N 2 ( z ) profiles, hence do not yield nearly adiabatic “mixed” layers. Our MIL results are consistent with the relation between the turbulent vertical velocity variance and energy dissipation rate proposed by Weinstock (1981) for the limited intervals evaluated.