Mathematics – Logic
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........52f&link_type=abstract
Thesis (PhD). UNIVERSITY OF COLORADO AT BOULDER, Source DAI-B 58/10, p. 5441, Apr 1998, 143 pages.
Mathematics
Logic
Scientific paper
The polar stratosphere in winter is influenced by planetary wave forcing and by radiative exchange with the underlying troposphere and surface. These affect the structure of the polar-night vortex, surf zone mixing, and the Brewer-Dobson circulation. The roles of mechanical and radiative forcing are examined through three-dimensional coupled dynamical- radiative simulations. The isentropic Primitive Equations are solved semi-spectrally on the sphere using vector Hough harmonics, a natural application of the well- developed theory of shallow-water motion to the analysis of baroclinic flow. Radiative influences are computed in detailed fashion under cloud-free conditions, with chemical distributions specified climatologically, consistent with the simulation's mechanistic viewpoint. Antarctica introduces a significant radiative equilibrium temperature anomaly in the lower polar stratosphere. This results from the radiative coupling of the lower stratosphere to the surface and troposphere through the 9.6 μm O3 band, in the atmospheric window. The anomaly drives significant changes in wind, temperature and diabatic transport during mean austral winter. These changes lower temperatures and increase descent rates within the vortex, while strengthening winds near the vortex edge. Antarctica's influence on polar dynamics follows from the symmetry between winds and radiative forcing in the southern hemisphere during southern winter. During northern winter this symmetry does not exist, and the radiative influence of the northern continents on the northern circulation is small. Hemispheric differences introduced by these disparate radiative influences have magnitudes locally comparable to observed hemispheric differences. During northern winter, large amplitude planetary wave forcing dominates tropospheric radiative influences. The primary role of the northern continents is wave generation through orography and diabatic effects. In southern winter, smaller planetary wave amplitudes allow the radiative influence of Antarctica to be expressed, so that radiative and planetary wave forcing both contribute significantly to the stratosphere's mean state during southern winter.
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