The general damping of climate variability by the ocean

N> t only does the ocean provide a moderating influence on the march of the seasons, but it also can provide a moderating influence on the variability of climate on other timescales too. We talk more about the mechanisms that give rise to climate variability in the next chapter, but for now let us just suppose that the climate system excluding the ocean is able to vary on multiple timescales, from days to years. Then, just as the ocean is able to damp the seasonal variability, the ocean damps...

The mechanism of El

The mean state of the atmosphere and the ocean Before discussing what processes conspire to produce El Ni o events, let us discuss what the mean state of the atmosphere and ocean are, beginning with the atmosphere. The trade winds throughout the equatorial region blow predominantly from higher latitudes toward the equator, and from the east to the west. The low-level convergence at the equator forces the air to rise and then, several kilometers above the surface, move poleward, sinking in the...

THE CORiOLiS FORCE

Another apparent force is caused by Earth's rotation, one that only arises when bodies are in motion relative to the rotating Earth, and this force is known as the Coriolis force after the French engineer and scientist Gaspard-Gustave Coriolis (1792-1843). It turns out to be much more important than the centrifugal force for currents and winds, although its effects are rather subtle. The sphericity of Earth is not important in the coriolis force itself, and until we get to the section on...

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.e., north-south and up-down in water depth) plane. 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...

Loss Of Sea iCE

Sea ice is formed by the freezing of seawater and so is to be found at high latitudes in both the Northern and Southern hemispheres, especially in their respective winters and springs. Sea ice is important to the climate system because it has a higher albedo than seawater (and therefore reflects back more solar radiation to space), because it affects the way the atmosphere and ocean exchange heat and water vapor, and because when sea ice forms, salt is extruded into the ocean, and when it...

A simple radiation model

Let us put aside the spatial variation of solar radiation for a while and try to obtain an estimate of the average surface temperature on Earth, given the average solar radiation coming in at the top of the atmosphere. Solar radiation causes Earth's surface to warm and emit its own radiation back to space, and the balance between incoming and outgoing radiation determines the average temperature of Earth's surface and of the atmosphere. To calculate the temperature, we need to know a few pieces...

The horizontal structure and the ocean currents

A schematic of the main horizontal ocean currents at the ocean surface is shown in figure 2.3. In most regions of the world, these currents extend a few hundred meters into the ocean, with the exception of the equatorial region. Here there is a shallow westward-flowing surface current and a more substantial eastward flow beneath (as well as narrow countercurrents on either side of the westward flow, not shown in the schematic). At first glance, the circulation seems complicated, especially as...

Torques and interior flow

If the wind stress acting on the ocean varies with latitude as we see that it does in figure 4.3 then the wind provides a torque that tends to spin the ocean. In a steady state, not only do the forces on the ocean have to balance but so do the torques otherwise the ocean would spin faster and faster. The torques on the ocean are provided by the wind, by friction, and by the Coriolis force (the pressure gradient does not provide a torque).2 Integrated over the entire ocean basin, the wind torque...

A simple mathematical model of the greenhouse effect

Let us now construct a simple mathematical model illustrating the greenhouse effect. our purpose in doing so is to see somewhat quantitatively, if approximately, whether the atmosphere might warm the surface up to the observed temperature. Let us make the following assumptions 1. The surface and the atmosphere are each characterized by a single temperature, Ts and Ta, respectively. 2. The atmosphere is completely transparent to solar radiation. 3. Earth's surface is a blackbody. 4. The...