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Frontogenesis and Turbulence: A Numerical Simulation

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  • 1 College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
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Abstract

A numerical simulation is analyzed that resolves the full range of motions from rotationally dominated, growing baroclinic waves to quasi-isotropic, three-dimensional shear instabilities. The results confirm a 40-yr-old prediction, made by B. Hoskins and F. Bretherton, that frontogenetic collapse of cross-frontal spatial scales, driven by baroclinic-wave deformation fields, will continue to the Kelvin–Helmholtz (K–H) turbulent transition. This process of frontal collapse followed by K–H transition provides a mechanism for spontaneous loss of balance in an initially geostrophic flow, and a direct, spectrally nonlocal pathway for downscale energy transfer that is phenomenologically distinct from traditional concepts of turbulent cascades and can contribute substantially to total kinetic energy dissipation. These results, which neglect surface drag and several other potentially relevant atmospheric processes, would suggest that the turbulence associated with collapsing fronts in the atmosphere can extend upward from the surface through roughly one-third of the troposphere.

© 2016 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author address: R. M. Samelson, College of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Admin. Bldg., Oregon State University, Corvallis, OR 97331-5503. E-mail: rsamelson@coas.oregonstate.edu

Abstract

A numerical simulation is analyzed that resolves the full range of motions from rotationally dominated, growing baroclinic waves to quasi-isotropic, three-dimensional shear instabilities. The results confirm a 40-yr-old prediction, made by B. Hoskins and F. Bretherton, that frontogenetic collapse of cross-frontal spatial scales, driven by baroclinic-wave deformation fields, will continue to the Kelvin–Helmholtz (K–H) turbulent transition. This process of frontal collapse followed by K–H transition provides a mechanism for spontaneous loss of balance in an initially geostrophic flow, and a direct, spectrally nonlocal pathway for downscale energy transfer that is phenomenologically distinct from traditional concepts of turbulent cascades and can contribute substantially to total kinetic energy dissipation. These results, which neglect surface drag and several other potentially relevant atmospheric processes, would suggest that the turbulence associated with collapsing fronts in the atmosphere can extend upward from the surface through roughly one-third of the troposphere.

© 2016 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author address: R. M. Samelson, College of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Admin. Bldg., Oregon State University, Corvallis, OR 97331-5503. E-mail: rsamelson@coas.oregonstate.edu
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