The meridional structure of the atmosphere

5.1. Radiative forcing and temperature

5.1.1. Incoming radiation

5.1.2. Outgoing radiation

5.1.3. The energy balance of the atmosphere

5.1.4. Meridional structure of temperature

5.2. Pressure and geopotential height

5.3. Moisture

5.4. Winds

5.4.1. Distribution of winds

5.5. Further reading

5.6. Problems

In previous chapters we considered those processes that play a role in setting the vertical distribution of atmospheric properties. Here we discuss how these properties vary horizontally, on the global scale. We shall see that geometrical effects play a major role in setting the observed horizontal distribution. The spherical Earth intercepts an essentially parallel beam of solar radiation, and so the incoming flux per unit surface area is greater at the equator than at the poles. An obvious and important consequence is that the atmosphere in the equatorial belt is warmer (and hence more moist)

than the atmosphere over the polar caps. As we will discuss in this and subsequent chapters, these horizontal temperature gradients induce horizontal pressure gradients and hence motions, as sketched in Fig. 5.1. The resulting atmospheric wind patterns (along with ocean currents) act to transport heat from the warm tropics to the cool high latitudes, thereby playing a major role in climate.

In this chapter then we will describe the observed climatology1 of atmospheric temperature, pressure, humidity, and wind.

1Here "climatology" implies some appropriate long-term average, such as the annual mean or seasonal mean, averaged over many years. In many of the figures shown here, the data are also averaged over longitude.

FIGURE 5.1. The atmosphere is warmer in the equatorial belt than over the polar caps. These horizontal temperature gradients induce, by hydrostatic balance, a horizontal pressure gradient force "P" that drive rings of air poleward. Conservation of angular momentum induces the rings to accelerate eastwards until Coriolis forces acting on them, "C," are sufficient to balance the pressure gradient force "P," as discussed in Chapters 6 and 7.

FIGURE 5.1. The atmosphere is warmer in the equatorial belt than over the polar caps. These horizontal temperature gradients induce, by hydrostatic balance, a horizontal pressure gradient force "P" that drive rings of air poleward. Conservation of angular momentum induces the rings to accelerate eastwards until Coriolis forces acting on them, "C," are sufficient to balance the pressure gradient force "P," as discussed in Chapters 6 and 7.

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