Hydrodynamics of Large Lakes

Abstract

difficult nonlinear terms in the equations of motion could be neglected. The resulting linearized equations are akin to those of acoustics, and solutions could be found with a variety of realistic boundary conditions. The same equations adequately describe some other large-scale atmospheric and oceanic motions, and it is therefore no surprise that much can be learned with their aid about large-scale motions in lake s. The equations of tidal theory were in fact used with great success in elucidating the properties of seiches and internal seiches in small and moderate size lakes. A seiche is a back-and-forth oscillation of lake level, much like the sloshing of water in· a bathtub. There is a large literature on seiches (for a recent review see Wilson 1972) and its dynamics is well understood. An internal seicpe is a similar motion of the cold, bottom layer of a stratified lake, the interface between cold and warm layers (the thermocline) playing the role of a free surface, although the interface displacements are very much larger in an internal seiche than surface dis­ plac ements in an ordinary seiche. Internal seiches in small lakes have also been understood for three quarters of a century (see e.g. Mortimer 1953). During the last decade or so considerable further advances have been made in the understanding of motions in lakes so large that the effects of the earth's rotation play an important role. These advances were also achieved with the aid of linearized equations (containing Coriolis force terms), with some assist from the conservation of potential vorticity. Platzman (1963) ha s treated in detail the effects of Coriolis force on seiches in large homogeneous lakes. Here we discuss some other in teres ting hydrodynam ic phenomena involving density stratification, which occur in large lakes and for which we have recently acqu ired a reasonable degree of dynamical insight. Originally this review started out with the tentative title circulation and