2-D Gyre Models
File last modified 23 November 1998
21.1 Introduction and Goals
Certainly, one of our goals in oceanography is to understand how material moves through the ocean. By "move" we mean not only the direct advection of substance by ocean currents, but also how this material is dispersed by chaotic, random motions characteristic of turbulent flow. Further, if we are to understand the large scale biogeochemical processing of material, we must understand how biological and chemical processes combine with these physical motions to affect geochemical distributions.
One of the ways to do this is to study the distributions of properties for which we have a clear idea about their biogeochemical properties, perhaps to the extent of them being inert If we can then use them to distinguish the physical processes first, we can later go beyond them to infer rates of biological and chemical processing. An example of this approach can be seen in our treatment of the one-dimensional open ocean advection-diffusion equations: first solve the "physics" and then solve the "chemistry".
Transient tracers (those tracers which are man-made and changing with time) and radioactive tracers offer the time-clock information we can use to solve these problems. Watching transient tracer distributions evolve represents a very powerful tool for diagnosing rates of ocean processes (and in particular ventilation). However, how do we go from these observations back to the basic process rates? One answer lies in performing model simulations with idealized circulation schemes, introducing the tracer to the model in the same way as you think occurs in nature, and then compare the model simulations to observations. We did a little of this, not with transient tracers, but cyclically varying tracers (gases) with the pwp-model.
In our progress from one-dimensions to higher dimension models, we will first study a simple two-dimensional model calculation, one which is similar, but of course much more polished, than the gyre model we study in problem set #10. We'll sketch a little history of how and why the model was developed. Second, we'll discuss a very interesting paper on tracer "ages" which uses a 2-D gyre model to explore non-ideal behavior of certain tracer age systems. As a preface to that effort, we'll digress into the concept of tracer age dating.
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