tailieunhanh - Environmental Fluid Mechanics - Chapter 9

Cơ học chất lỏng Địa vật lý thường giao dịch với dòng chảy của phạm vi không gian lớn. Có nhiều đối tượng nằm trong thể loại này, bao gồm các dòng hải lưu, thủy triều, cửa sông, dòng chảy ven biển, và những người khác. Trong chương này, chúng tôi tập trung vào chuyển động vòng xoay của trái đất, đặc biệt là hạn Coriolis, quan trọng là trong các phương trình của chuyển động. Tình trạng này phát sinh vấn đề với quy mô lớn không gian, mà kết quả trong số Rossby gần một hoặc ít hơn | 9 Geophysical Fluid Motions INTRODUCTION Geophysical fluid mechanics generally deals with flows of large spatial extent. There are many subjects that fall within this category including ocean currents tides estuaries coastal flows and others. In the present chapter we focus on motions for which the rotation of the earth in particular the Coriolis term is important in the equations of motion. This condition arises in problems with large spatial scales which result in Rossby numbers approaching one or less. Recall from Chap. 2 that the Rossby number is defined as the ratio of characteristic velocity to the product of characteristic length and rotation rate. This is derived from the ratio of the relative magnitude of the nonlinear acceleration terms to the Coriolis terms in the equations of motion as shown in Sec. . Here we modify this definition slightly to be more consistent with the literature in this field using U fL where Ro Rossby number U characteristic velocity L characteristic length and f Coriolis parameter or planetary vorticity 2Q0 sin Ỷ where Q0 is the angular rotation rate of the earth and Ỷ is the latitude. The magnitude of f varies between X 10 4 s 1 at the poles to zero at the equator. Referring back to Table Rossby numbers that are sufficiently small that rotation effects become important are associated with large lakes estuaries coastal regions and oceanic currents. Atmospheric motions also are subject to Coriolis effects but the present discussion focuses on aqueous systems. In addition to the inclusion of the Coriolis terms an interesting feature of the analysis of fluid motions in very large systems is the relative unimportance of solid boundaries. This sometimes poses difficulties in specifying boundary conditions since the location of the boundaries is not well-defined. Copyright 2001 by Marcel Dekker Inc. All Rights Reserved. The only clear boundary in the deep oceans for instance is the air water interface. Boundaries do