Irv gives rainv climateoff sea

gives rainy climate

Figure 1.9. How the rain-making machine of the tropics works. The heating of the ITCZ causes water to condense out and fall as rain. When the air descends again, no water vapor can condense out and there is an arid climate.

it cools, and water droplets condense out as clouds and then fall as rain. This gives the moist tropical rainforest climate down below.

A typical morning in the equatorial tropics begins clear and sunny. As the sun climbs high in the sky. the day becomes hot, but by mid-afternoon clouds begin to build and cover the sky as the heat of the sun sets olT convection in the atmosphere. Eventually, by late afternoon the heat of the day is broken by a thunderstorm, leaving the air fresh and mild, and the vegetation moist with rain.

Hundreds of kilometers farther north and south, the air carried aloft in the ITCZ descends back down to earth. It has lost its moisture, which fell as rain as it first rose up from the surface, and now it also warms as it descends (Figure 1.9). The air is already dry, and the warming makes it hold onto its small amount of water vapor even more tightly, so there is no chance of rain falling from it. These bands of descending air. north and south of the Equator, tend to give desert climates with hardly any rainfall. Ilcncc the same mechanism that produced very wet climates along the equator also produces arid climatcs to the north and south.

The ITCZ does not just stay static. It wavers north and south during the year, because the earth is tilted relative to the sun (this giving winter and summer, as explained earlier). So the highest point of sun in the sky, relative to your point of view on the ground, moves north and south of the equator. Thus, the strongest zone

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