Atmospheric Cycle

Heat from the Sun warms the Earth. As we saw in our discussion of heat, air which is so heated will rise, which results in a low pressure area. Nearby colder air higher up in the atmosphere will subsequently fall, resulting in a high pressure area. Air then flows between high and low pressure areas of the earth, resulting in what is called the atmospheric cycle. This movement can be on a local or a global scale.

  High and low pressure areas are indicated on weather maps, such as in the following example.

 

Figure 14.7: Weather map

High pressure areas are usually associated with clear skies and stable weather. Low pressure areas, on the other hand, are usually associated with unstable weather, due to a high pressure area moving in, and also with cloudy skies, due to the increased evaporation of moisture in the upper atmosphere coming from the rising air. Also on this map are indicated fronts: a cold front, with cold air behind it, is indicated by lines with triangles, and a warm front, with warm air behind it, is indicated by lines with semi-circles. The fronts move in the direction shown by the triangles or circles, and where two fronts meet usually changing weather, such as a storm, results.