The influence of planetary-wave transience on horizontal air motions in the stratosphere
- Univ. of Colorado, Boulder, CO (United States)
The influence of large-scale transience on horizontal air motions and tracer distributions in the stratosphere is explored in equivalent barotropic calculations. Planetary waves are excited by steady and unsteady components of mechanical forcing that are assigned variances typical of variability in the stratosphere. Two classes of transience are considered. A monochromatic traveling wave, representative of discrete components such as the 5- and 16-day waves, is imposed as unsteady mechanical forcing. The response of each of these forms of unsteady forcing is investigated in terms of the characteristic time scale of the transience. For monochromatic transience, eddy transport is concentrated inside the critical region of the traveling wave. During constructive interference, eddy displacements of the traveling wave reinforce those of the stationary wave. The nonlinear interaction that takes place between the two components leads to an expanded critical region and more extensive transport. Eddy transport is weaker locally than that concentrated inside the critical region of a monochromatic traveling wave with the same variance. Transience distributed over a wide range of frequency produces less overall transport than transience concentrated at low frequencies (e.g., spectrally [open quotes]red[close quotes]). Stochastic forcing also excited westward-propagating transients that radiate into the summer hemisphere and disperse globally into planetary normal modes. Favored in the response to broadband forcing, those discrete components lead to behavior similar to that of traveling waves excited by monochromatic forcing. By introducing nonconservative behavior in regions where they reinforce large displacements of the stationary wave and where they themselves are Doppler shifted to small intrinsic phase speeds, these unsteady components can contribute to the momentum budgets of both the wintertime and the summertime circulations. 17 refs., 33 figs.
- OSTI ID:
- 5583645
- Journal Information:
- Journal of the Atmospheric Sciences; (United States), Vol. 49:5; ISSN 0022-4928
- Country of Publication:
- United States
- Language:
- English
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