Other
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........95c&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF ILLINOIS AT URBANA -CHAMPAIGN, 1992.Source: Dissertation Abstracts International, Volume: 53-01,
Other
Tropopause, Ep Flux
Scientific paper
The following problems: (1) The effects of wave transience on the propagation of planetary waves in the stratosphere; (2) The coupling of the equatorial and extratropical quasi-biennial oscillations; and (3) The propagation of planetary waves between the troposphere and stratosphere; are investigated in this thesis. Two distinct maxima in the EP-flux convergence, one below the stratospheric polar jet and the other north of the zero wind line in the tropics, are found for steady and transient waves in a variety of realistic zonal flows in the Northern Hemisphere winter stratosphere, suggesting that the bimodal structure in the EP-flux convergence in observations (e.g., Randel and Held 1991) is a general feature of the winter stratosphere. The maximum in the tropics is due to the linear critical line absorption of meridionally propagating waves (e.g., Dickinson 1970), and the maximum in high latitudes is caused by the dissipation of highly non-WKBJ waves at local maximum of the refractive index at a jet. The existence and location of the maximum in the EP-flux convergence in high latitudes are insensitive to transience. Its strength, however, is very sensitive to transience, and the sensitivity is much larger for wave 2. The equatorial wind QBO affects strongly the propagation of planetary waves, and produces a significant QBO in the EP-flux divergence in high latitudes. The QBO in high latitudes reveals a layered structure in the vertical, and its vertical patterns agree well with the vertical shears of the wind QBO at the equator. The QBO in the EP-flux divergence in high latitudes is primarily due to the change of the refractive index there. The change of the refractive index in high latitudes is mainly caused by the change of the zonal-mean thermal anomalies there, which, in turn, are induced by the changes of the equatorial winds through the thermal wind balance. There is also a maximum in the EP-flux convergence in the upper troposphere in high and middle latitudes. The formation of this maximum is due to the dissipation of non-WKBJ waves near a local maximum of the refractive index at the tropopause. The local maximum in refractive index at the tropopause is caused by the vertical gradient of the buoyancy frequency and the vertical shear of the zonal flow there. The tropopause acts like a valve for the upward propagation of planetary waves. The key controlling parameters are the vertical gradient of the buoyancy frequency and the vertical shear of the zonal winds at the tropopause. A smaller vertical gradient of the buoyancy frequency and a smaller vertical shear of the zonal flow at the tropopause enhance the upward propagation of planetary waves.
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