Aviation Weather

full text of the classic FAA guide

HEAT AND TEMPERATURE

Heat is a form of energy. When a substance contains heat, it exhibits the property we measure as temperature—the degree of “hotness” or “coldness.” A specific amount of heat absorbed by or removed from a substance raises or lowers its temperature a definite amount. However, the amount of temperature change depends on characteristics of the substance. Each substance has its unique temperature change for the specific change in heat. For example, if a land surface and a water surface have the same temperature and an equal amount of heat is added, the land surface becomes hotter than the water surface. Conversely, with equal heat loss, the land becomes colder than the water.

The Earth receives energy from the sun in the form of solar radiation. The Earth and its atmosphere reflect about 55 percent of the radiation and absorb the remaining 45 percent converting it to heat. The Earth, in turn, radiates energy, and this outgoing radiation is “terrestrial radiation.” It is evident that the average heat gained from incoming solar radiation must equal heat lost through terrestrial radiation in order to keep the earth from getting progressively hotter or colder. However, this balance is world-wide; we must consider regional and local imbalances which create temperature variations.

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