### Abstract

A long unresolved issue in nonorographic gravity wave generation is whether there is significant emission from Kelvin-Helmholtz (KH) shear instability in the lower stratosphere, for instance, just above tropopause jets. Such emission has often been suggested as significant for the angular momentum budget and hence for the wave-driven circulation of the middle atmosphere, most crucially in the summer mesosphere. An idealized model thought experiment is studied in which it is assumed that the KH shear instability rapidly mixes a thin layer, producing a "pancake" of three-dimensional clear-air turbulence, and emitting low-frequency inertia-gravity waves whose aspect ratio matches that of the turbulent layer and whose horizontal wavelength is large enough to avoid back-reflection and hence reach the summer mesosphere. The wave emission is modeled as a linear initial-value problem in which the rapid mixing of mass and momentum achieved by the turbulence is treated as instantaneous, and hence as determining the initial conditions. Care is taken to cast the problem into a form that permits well-conditioned numerical evaluation of the analytical solution, in both rotating and nonrotating cases, which behave very differently. Comparison with fully nonlinear numerical simulations in two dimensions of the same initial-value problem indicates that the linear theory is much better than might be expected on order-of-magnitude grounds. A companion paper (Part II) investigates the transmission of the emitted waves to the mesosphere subject to refraction and radiative damping.

Original language | English (US) |
---|---|

Pages (from-to) | 3749-3763 |

Number of pages | 15 |

Journal | Journal of the Atmospheric Sciences |

Volume | 56 |

Issue number | 21 |

State | Published - Nov 1 1999 |

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### ASJC Scopus subject areas

- Atmospheric Science

### Cite this

*Journal of the Atmospheric Sciences*,

*56*(21), 3749-3763.

**On shear-generated gravity waves that reach the mesosphere. Part I : Wave generation.** / Buhler, Oliver; McIntyre, Michael E.; Scinocca, John F.

Research output: Contribution to journal › Article

*Journal of the Atmospheric Sciences*, vol. 56, no. 21, pp. 3749-3763.

}

TY - JOUR

T1 - On shear-generated gravity waves that reach the mesosphere. Part I

T2 - Wave generation

AU - Buhler, Oliver

AU - McIntyre, Michael E.

AU - Scinocca, John F.

PY - 1999/11/1

Y1 - 1999/11/1

N2 - A long unresolved issue in nonorographic gravity wave generation is whether there is significant emission from Kelvin-Helmholtz (KH) shear instability in the lower stratosphere, for instance, just above tropopause jets. Such emission has often been suggested as significant for the angular momentum budget and hence for the wave-driven circulation of the middle atmosphere, most crucially in the summer mesosphere. An idealized model thought experiment is studied in which it is assumed that the KH shear instability rapidly mixes a thin layer, producing a "pancake" of three-dimensional clear-air turbulence, and emitting low-frequency inertia-gravity waves whose aspect ratio matches that of the turbulent layer and whose horizontal wavelength is large enough to avoid back-reflection and hence reach the summer mesosphere. The wave emission is modeled as a linear initial-value problem in which the rapid mixing of mass and momentum achieved by the turbulence is treated as instantaneous, and hence as determining the initial conditions. Care is taken to cast the problem into a form that permits well-conditioned numerical evaluation of the analytical solution, in both rotating and nonrotating cases, which behave very differently. Comparison with fully nonlinear numerical simulations in two dimensions of the same initial-value problem indicates that the linear theory is much better than might be expected on order-of-magnitude grounds. A companion paper (Part II) investigates the transmission of the emitted waves to the mesosphere subject to refraction and radiative damping.

AB - A long unresolved issue in nonorographic gravity wave generation is whether there is significant emission from Kelvin-Helmholtz (KH) shear instability in the lower stratosphere, for instance, just above tropopause jets. Such emission has often been suggested as significant for the angular momentum budget and hence for the wave-driven circulation of the middle atmosphere, most crucially in the summer mesosphere. An idealized model thought experiment is studied in which it is assumed that the KH shear instability rapidly mixes a thin layer, producing a "pancake" of three-dimensional clear-air turbulence, and emitting low-frequency inertia-gravity waves whose aspect ratio matches that of the turbulent layer and whose horizontal wavelength is large enough to avoid back-reflection and hence reach the summer mesosphere. The wave emission is modeled as a linear initial-value problem in which the rapid mixing of mass and momentum achieved by the turbulence is treated as instantaneous, and hence as determining the initial conditions. Care is taken to cast the problem into a form that permits well-conditioned numerical evaluation of the analytical solution, in both rotating and nonrotating cases, which behave very differently. Comparison with fully nonlinear numerical simulations in two dimensions of the same initial-value problem indicates that the linear theory is much better than might be expected on order-of-magnitude grounds. A companion paper (Part II) investigates the transmission of the emitted waves to the mesosphere subject to refraction and radiative damping.

UR - http://www.scopus.com/inward/record.url?scp=0039183564&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0039183564&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0039183564

VL - 56

SP - 3749

EP - 3763

JO - Journals of the Atmospheric Sciences

JF - Journals of the Atmospheric Sciences

SN - 0022-4928

IS - 21

ER -