tailieunhanh - Physical Processes in Earth and Environmental Sciences Phần 9

Chương 6 Các mô hình chính của dòng chảy dốc từ mặt biển tính năng động. Lưu ý sự kiểm soát của các vectơ hiện tại (cả độ lớn và hướng) bởi độ lớn của gradient không gian trong địa hình nước. | 258 Chapter 6 Fig. The remarkable satellite-measured topography of the mean sea surface with wave and tidal wave effects subtracted . Fig. The major pattern of gradient flow from the computed dynamic sea surface. Note the control of current vectors both magnitude and direction by the magnitude of the spatial gradients in water topography that is OBL flow is parallel to the gradient lines with an intensity proportional to grayscale thickness. Note western intensification of Pacific Kuroshio KS and Atlantic Gulf Stream GS currents and the strong circumpolar Antarctic current AC . though complex meandering filament of warm Caribbean water in transit to the shores of northwest Europe Figs and . In the mid-twentieth century Stommel explained these most striking features of the general oceanic circulation by a consideration of both lateral friction and conser vation of angular momentum. We have seen that all moving fluid masses possess vorticity appropriate to the latitude in which they find themselves Section and that the total or absolute vorticity Ỉ must be conserved. Thus a northward-moving mass of water impelled by wind shear to spin clockwise will gain planetary vorticity as it moves. In order to keep Outer Earth processes and systems 259 Fig. The Gulf Stream is usually a continuous though complex meandering filament of warm Caribbean water in transit to the shores of northwestern Europe. In these satellite images an unusually strong north wind has driven cool waters from the Mid Atlantic Bight across the track of the Gulf Stream breaching it as a cool tongue that is eventually itself transported north and east in the main current. Main northern margin to Gulf Stream is a boundary shear layer sl . 80 w 70 w 60 w 45 N 39 N 33 N 27 N I I J I 0 I I I -50cm -30cm -10 10 30 50 cm sea surface height 1 m of topography over a typical eddy length of c. 250 km gives a mean slope of 1 250 000 note the asymetric slopes caused by radial flow around