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- Title
Baroclinic Instability in High Latitudes Induced by Polar Vortex: A Connection to the Arctic Oscillation.
- Authors
Tanaka, H. L.; Tokinaga, Hiroki
- Abstract
In this study, baroclinic instability of the northern winter atmosphere is investigated in the context of the dynamical interpretation of the Arctic oscillation. The unstable solutions, obtained by a method of 3D normal mode expansion, are compared for observed zonal basic states with strong and weak polar vortices in reference to the Arctic oscillation index. As a result of the eigenvalue problem of the linear stability analysis, a characteristic unstable solution is obtained that dominates in high latitudes when the polar vortex is strong. The mode is called a monopole Charney mode M[sub 1] , which is similar to an ordinary Charney mode M[sub C] in midlatitudes. In order to understand the origin of the M[sub 1] mode, a hypothetical zonal basic state that has only the polar jet with no subtropical jet is analyzed. It is found that the M[sub 1] mode in high latitudes is excited by the baroclinicity associated with the polar vortex. The M[sub 1] mode in high latitudes is dynamically the same Charney mode as M[sub C] but is excited by the baroclinicity of the polar jet instead of the subtropical jet. As the M[sub C] mode intensifies the subtropical jet by the eddy momentum transfer, the M[sub 1] mode transfers eddy momentum to high latitudes to intensify the polar jet. Since M[sub 1] mode appears during the strong polar jet and feeds the westerly momentum to the polar jet, there is a positive feedback between the M[sub 1] mode and the polar vortex. This positive feedback would produce a persistent strong polar jet, which may in tern result in the occurrence of the annular mode of the Arctic oscillation.
- Subjects
ARCTIC regions; ATMOSPHERIC research; BAROCLINICITY; OSCILLATIONS; POLAR vortex
- Publication
Journal of the Atmospheric Sciences, 2002, Vol 59, Issue 1, p69
- ISSN
0022-4928
- Publication type
Article
- DOI
10.1175/1520-0469(2002)059<0069:BIIHLI>2.0.CO;2