## NTRS - NASA Technical Reports Server

Propagation and Breaking at High Altitudes of Gravity Waves Excited by Tropospheric ForcingAn anelastic approximation is used with a time-variable coordinate transformation to formulate a two-dimensional numerical model that describes the evolution of gravity waves. The model is solved using a semi-Lagrangian method with monotone (nonoscillatory) interpolation of all advected fields. The time-variable transformation is used to generate disturbances at the lower boundary that approximate the effect of a traveling line of thunderstorms (a squall line) or of flow over a broad topographic obstacle. The vertical propagation and breaking of the gravity wave field (under conditions typical of summer solstice) is illustrated for each of these cases. It is shown that the wave field at high altitudes is dominated by a single horizontal wavelength; which is not always related simply to the horizontal dimension of the source. The morphology of wave breaking depends on the horizontal wavelength; for sufficiently short waves, breaking involves roughly one half of the wavelength. In common with other studies, it is found that the breaking waves undergo "self-acceleration," such that the zonal-mean intrinsic frequency remains approximately constant in spite of large changes in the background wind. It is also shown that many of the features obtained in the calculations can be understood in terms of linear wave theory. In particular, linear theory provides insights into the wavelength of the waves that break at high altitudes, the onset and evolution of breaking. the horizontal extent of the breaking region and its position relative to the forcing, and the minimum and maximum altitudes where breaking occurs. Wave breaking ceases at the altitude where the background dissipation rate (which in our model is a proxy for molecular diffusion) becomes greater than the rate of dissipation due to wave breaking, This altitude, in effect, the model turbopause, is shown to depend on a relatively small number of parameters that characterize the waves and the background state.
Document ID
19990007911
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Prusa, Joseph M.
(Iowa State Univ. of Science and Technology Ames, IA United States)
Smolarkiewicz, Piotr K.
(National Center for Atmospheric Research Boulder, CO United States)
Garcia, Rolando R.
(National Center for Atmospheric Research Boulder, CO United States)
Date Acquired
August 19, 2013
Publication Date
August 1, 1996
Publication Information
Publication: Journal of the Atmospheric Sciences
Volume: 53
Issue: 15
Subject Category
Geophysics
Funding Number(s)
CONTRACT_GRANT: NASA Order L-99120-C
CONTRACT_GRANT: NAGw-4060
Distribution Limits
Public