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Fundamentals Of Geophysical Fluid Dynamics Part 9

Phương pháp Euler: Nghiên cứu vận tốc của phần tử chất lỏng tại nhiều điểm trong dòng chảy ở những thời điểm khác nhau. (Hình vẽ trên) Ví dụ: Xét một điểm M có toạ độ x,y,z cố định trong không gian chứa chất lỏng chuyển động và một phần tử chất lỏng chuyển động với vận tốc u qua điểm M tại thời gian t. | 6.2 Oceanic Wind Gyre and Western Boundary Layer 261 Fig. 6.19. A meridional cross-section at mid-longitude in the basin in an 8-layer model of a double wind-gyre. Top Mean zonal velocity u y z . The contour interval is 0.05 m s 1 showing a surface jet maximum of 0.55 m s 1 a deep eastward flow of 0.08 m s and a deep westward recirculation-gyre flow 0.06 m s 1. Bottom Eddy kinetic energy 1 u0 2 y z . The contour interval is 10 2 m2 s 2 showing a surface maximum of 0.3 m2 s 2 and a deep maximum of 0.02 m2 s 2. Holland 1986. 262 Boundary-Layer and Wind-Gyre Dynamics eddies because of the averaging. The Sverdrup gyre circulation is evident cf. Fig. 6.14 primarily in the upper ocean and away from the strong boundary and separated jet currents. At greater depth and in the neighborhood of these strong currents are recirculation gyres whose peak transport is several times larger than the Sverdrup transport. These recirculation gyres arise in response to downward eddy momentum flux by isopycnal form stress cf. Sec. 5.3.3 . The separated time-mean jet is a strong narrow surface-intensified current Fig. 6.19 top . Its instantaneous structure is vigorously meandering and has a eddy kinetic energy envelope that extends widely in both the horizontal and vertical directions away from the mean current that generates the variability Fig. 6.19 bottom . Overall the mean currents and eddy fluxes and their mean dynamical balances have a much more complex spatial structure in turbulent wind gyres than in zonal jets. While simple analytic models of steady linear gyre circulations Sec. 6.2.2 and their normal-mode instabilities e.g. as in Secs. 3.3 and 6.2 provide a partial framework for interpreting the turbulent equilibrium dynamics obviously they do so in a mathematically and physically incomplete way. The eddy-mean interaction includes some familiar features e.g. Rossby waves and vortices barotropic and baroclinic instabilities turbulent cascades of energy and enstrophy and .