chapter  11
12 Pages

Electricity from the wind

Winds are generated by uneven heating of the Earth and its atmosphere by the sun. The Earth is generally warmest at the equator. As the air there is heated, it expands. (Remember Charles and GayLussac-increasing the temperature of a gas increases its volume.) The same mass of air now occupies a larger volume, another way of saying that the density of that portion of air has decreased. Because the density has decreased, the air will rise. This expansion by heating and reduction of density is the origin of the bit of folk wisdom that ‘hot air rises.’ Two effects follow from the rising of heated air. First, cooler air

from elsewhere will flow into the region, to replace the heated air that has ascended into the atmosphere. This flow of air is felt as a wind. The second effect is that the heated air will travel at high altitudes until it cools. As it cools, its volume decreases (Charles and Gay-Lussac again) and it becomes more dense. In doing so, it sinks to lower elevations. Essentially, a gigantic ‘conveyor belt’ of air movement has been

established. Air masses that benefit by being warmed by the sun rise, and are replaced by cooler air flowing into the region. At the same time, the warmed air travels away from the equator, cools,

and sinks, replacing some of the cooler air that had moved toward the equator. These large circulation patterns owe their origin to the differential heating of Earth by the sun.