Add to Basket. Book Description Princeton University Press, Condition: New. More information about this seller Contact this seller. The Cryosphere Princeton Primers in Climate. Publisher: Princeton University Press , This specific ISBN edition is currently not available. View all copies of this ISBN edition:. Synopsis About this title The cryosphere encompasses the Earth's snow and ice masses. From the Back Cover : "Distinguished glaciologist Shawn Marshall leads a lucid tour through the essentials of ice in the environment, with more than enough information to satisfy the casual student, and additional pointers to steer the serious scientist.
Be the first to write a review. Add to Wishlist. Ships in 7 to 10 business days. Link Either by signing into your account or linking your membership details before your order is placed. Description Table of Contents Product Details Click on the cover image above to read some pages of this book! Industry Reviews "In this work, part of the Princeton Primers in Climate series, glaciologist Marshall examines the nature of ice and snow the cryosphere in all its various forms In Stock.
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Reeds Maritime Meteorology Reeds Professional. Reeds Weather Handbook. The Cloudspotter's Guide. Reading the Clouds. A Short Introduction to Climate Change. Stage 1. The Cloud Collector's Handbook. The Antarctic Circumpolar Current At high latitudes, the Southern Hemisphere has a qualitatively different geometry than the Northern Hemisphere: the other continents do not connect to Antarctica, and so the oceans are free to circulate all the way around the globe, forming the Antarctic Circumpolar Current ACC.
The flow is predominantly zonal east—west and in that sense resembles that of the atmosphere. An enormous transport of water is sustained over great lengths, comparable to that of the great gyres. The strength of ocean currents is traditionally measured in sverdrups Sv , which are named after Harald Sverdrup, a famous Norwegian oceanographer working in the first half of the twentieth century. A sverdrup was originally defined as a volume transport of m3 s-1 of water, although nowadays it is also commonly used as a measure of mass flow, namely kg s-1 of water or 1 million metric tons of fluid per second.
The two definitions are not exactly equivalent because the density of water is not exactly 1, kg m-3, but in any case, the sverdrup is usually used in an informal, approximate way. In comparison, the Gulf Stream varies from about 30 Sv off the coast of Florida, increasing in strength as it flows northward and water joins it from the Atlantic, eventually peaking at about Sv after it 32 T h e O c e a n s: A D e s c r i p t i v e O v e r v i e w leaves the coast near Cape Hatteras in North Carolina. To give some perspective, the flow of the mighty Amazon River is about 0.
The overturning circulation and the vertical structure The meridional overturning circulation MOC of the ocean is the name commonly given to the circulation in the meridional i. Horizontal variations in this circulation can be important, but let us put them aside for now.
This circulation comes about as a consequence of various factors: the temperature gradient between equator and pole, the temperature difference between high northern latitudes and high southern latitudes, the winds, especially over the southern ocean, and turbulent mixing in the ocean interiors; we will discuss all of these more in chapter 4.
Suffice it to say now that the dense water at high latitudes sinks and moves equatorward in the deep ocean, filling the abyss in both hemispheres with water that is very cold and dense. The overturning circulation is much stronger in the Atlantic than in the Pacific because the water at high northern latitudes is saltier, and hence denser, in the Atlantic than in the Pacific, but in both basins the deep water is cold and dense. However, the upper ocean at lower latitudes contains warmer water circulating in the gyres, and this water extends down almost a kilometer deep.
The zonally averaged density in the Atlantic Ocean. Note the break in the vertical scale at 1, m. A typical vertical profile passing through the subtropical gyre might look something like the schematic shown in figure 2.
Schematic of the vertical structure of the ocean, emphasizing the mixed layer. In the mixed layer, typically 50— m deep, turbulence and convection act to keep the temperature relatively uniform in the vertical.
source url Below this layer, temperature changes over a depth of a few hundred meters, in the thermocline, before becoming almost uniform at depth, in the abyss. Adapted from Marshall and Plumb, The mixing comes about through mechanical stirring from the wind and by convection that occurs when the water becomes statically unstable—that is, when a denser patch of water lies on top of a lighter patch of water. The differences in density normally arise because of the temperature differences warmer water is light 35 chapter 2 but might also arise because of salinity effects saltier water is denser , for example, if evaporation produces salty water at the surface.
Typically, the mixed layer is about 50— m thick, but in places it might go much deeper if there is intense convection, which mostly occurs in high latitudes.
The thermocline and the abyss The thermocline is the layer of water in which temperature varies quite rapidly from the warmth of the mixed layer to the cold of the abyss, and typically it is —1, m thick. The abyss is a very thick layer of water that stretches from the base of the thermocline to the bottom of the ocean. The water in the abyss has its origins at high latitudes in both Northern and Southern hemispheres and so is cold and dense.
The thermocline may thus be regarded as a transition region, or boundary layer, connecting the cold abyss with the warm surface layers. It is a rather complicated transition region because a number of interacting physical processes occur there. First, the thermocline has a seasonal component because the temperature in the mixed layer varies with the seasons, whereas the abyssal temperature is almost constant year round. The temperature difference across the thermocline is thus larger in summer than in winter.
In the upper thermocline, the seasonal variations manifest themselves most. This region is called the seasonal thermocline, and it may be several tens of meters thick. The lower, unchanging part of the thermocline is called 36 T h e O c e a n s: A D e s c r i p t i v e O v e r v i e w the permanent thermocline, and this part is up to several hundred meters thick. The thermocline is not just a static transition between cold and warm waters; rather, it contains the circulating waters of the great gyres. Finally, we note that the thermocline is rather different in the subpolar gyres than in the subtropical gyres.
Typically, it is weaker in the former because the surface waters are already quite cold there, so there is less of a transition region—that is, a much less distinct thermocline. Nevertheless, the upper waters are still circulating and over most of the subpolar gyre there is still a thermocline, albeit a somewhat weak one. Global Ocean Circulation and Ocean Eddies Let us conclude this chapter with a short discussion of two important and rather different aspects of the ocean: if and how the ocean circulates as a whole and, at the opposite extreme, the role of mesoscale eddies.
How does it all fit together?
There is no universally accepted picture, and certainly no quantitative theory. Rather, observations and numerical simulations have been used to put together a qualitative picture, as illustrated in figure 2. The circulation illustrated should be regarded as a highly schematic representation, perhaps even as a metaphor, of the real ocean circulation, in part because of the presence of ocean eddies discussed below.
However, the figure does illustrate the main features of the global circulation: a meridional overturning circulation, the sinking of cold dense water in the North Atlantic and off Antarctica, and the western boundary currents. Ocean eddies We are all familiar with the fact that the weather differs from the climate, the difference arising because the atmospheric flow is unsteady, and we talk more about this in chapter 6.
In spite of their small scale, the ocean eddies are energetic—the total kinetic energy associated with the eddies in the ocean is about ten times larger than the kinetic energy in the mean currents. Nevertheless, the eddies do not completely destroy the mean flows or make them meaningless, although they can obscure them from easy view and straightforward measurement.
A full reconciliation of these contrasting views and an understanding of how they fit together are perhaps now coming into our reach, although tantalizingly beyond our grasp. The current chapter is a little more mathematical than the others in this book, but it requires no more sophistication on the part of the reader—perhaps less in fact. Nevertheless, some readers may prefer to read the later chapters first, referring back to the material here as needed.
The atmosphere and ocean are both fluids and, although one is a gas and the other a liquid, their motion is determined by similar physical principles and described by similar equations: the Navier—Stokes equations of fluid dynamics. It turns out that for most geophysical applications, the Coriolis force is much more important than centrifugal force, but we need to understand the latter to understand the former, so that is where we begin.
Centrifugal Force Suppose that you are riding in a train that starts to go around a bend rather quickly. You feel like you are being thrust outward toward the side of the car, and if you are really going quickly around a tight curve, you might have to hang onto something to stay put. The outward force that you are feeling is commonly known as centrifugal force. What is going on?
That is, to change either direction or speed, a body must be acted upon by a force. Thus, in order for you to go around a bend, a force must act and act on the train too , and this force, whatever it may be in a particular situation, is called the centripetal force. Without that force, you would continue to go in a straight line. The centrifugal force that you feel is caused by your inertia giving you a tendency to try to go in a straight line when your environment is undergoing a circular motion, so you feel that you are being pushed outward.
You do end up going around the bend because your seat pushes against you, providing a real force the aforementioned centripetal force that accelerates you around the bend. The centripetal force that makes the train go around the bend comes from the rails pushing on the train wheels. With this discussion in mind, we see that there are two ways to think about the force balance as you go around the bend literally.
There appear to be two forces acting on you: the centrifugal force pushing you out and the seat pushing back the centripetal force in the other direction. There is a simple formula for this force that is derived in appendix A to this chapter. A quite analogous situation occurs for us on Earth. Sitting on the surface of Earth, we must therefore experience a centrifugal force that is trying to fling us off into space.
The reason that we stay comfortably on the surface is that the force of gravity overwhelms the centrifugal force, as a quick calculation shows. The radius of Earth is about 6, km, so that using equation 3. The centrifugal effect is therefore quite small, although not so small that we cannot measure it.
The distance from the center of Earth to the surface is in fact some 30 km larger at the equator than at the poles.
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The centrifugal force is otherwise not terribly important, and its effect can be taken into account by slightly modifying the value of the gravitational force as necessary. It turns out to be much more important than the centrifugal force for currents and winds, although its effects are rather subtle. To gain an intuitive idea of what the coriolis force is, consider the hopefully fanciful situation in which a missile is launched from the North Pole toward the equator, as illustrated in figure 3.
Suppose the missile is initially aimed at Africa and that it takes about six hours for the missile to reach the equator. When the missile reaches the equator, Earth has rotated a quarter turn, but the missile has not and so it will land in South America!
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