중위도 대기 대순환의 역학적 메커니즘 규명: 이론적 틀 제시

Abstract

The general circulation in mid-latitudes is characterized by planetary geostrophic motion, where heat and momentum fluxes from synoptic eddies play a crucial role. The poleward heat flux, produced by baroclinic eddy growth, reduces the meridional temperature gradient and is parameterized as eddy diffusion. Similarly, eddy momentum flux, driven by barotropic wave breaking, is assumed proportional to the horizontal shear of the zonal mean zonal wind, intensifying upper-level westerlies. Incorporating turbulent eddy parameterizations into the planetary- scale heat equation, a balance is achieved between the two fluxes, resulting in eddy-driven circulations in mid-latitudes akin to the Farrell cell. The meridional domain is governed by a fourth-order characteristic equation, exhibiting two primary features related to anomalous potential temperature. The first feature is a linear decline in anomalous potential temperature, inducing westerly winds in midlatitudes. The second feature, represented by a trigonometric function, corresponds to jet streams generated by eddy momentum flux. The meridional structure of the circulation is influenced by three factors. The first factor is a structural number D/SM, where D represents eddy diffusivity, S signifies dry static stability, and M is the proportionality constant for momentum flux, summarizing the life cycle of synoptic eddies. The second factor relates to planetary size relative to the external Rossby deformation radius. Finally, a vertical structure of the atmosphere, associated with eigenvalues of the vertical mode in the main heat equation, constitutes the third factor. The combination of these three factors within the characteristic equation determines the location and number of eddy-driven circulations in mid-latitudes.