| Regions of sinking air are called highs, high pressure regions or anticyclones. Clear skies and fair weather usually occur in theseregions.Regions of rising air are called lows, low pressure regions, depressions or cyclones. Clouds rain and strong winds often occur in these regions.See high pressure system, low pressure system, coldfronts and parcels of air for more detailed and information.Look at the map below (Figure 1). This shows a typical pattern of high and low pressure regions. The curved blue lines are called isobars.These pass through areas with the same air pressure.Air pressure is measured in hectopascals. On this weather map the isobars are at 4 hectopascal intervals.The black arrows show the wind direction. Highand low pressure regions do not stay in the same place. They move over the Earth's surface.The purple line with barbs is a cold front. The barbs point in the direction the front is moving. In thediagram below (Figure1) the cold front is moving in an easterly direction.Figure 1
A simple weather map showing low (L) and high (H) pressure regions, wind direction,
a ridge of high pressure and acold front (the purple barbed line). The animations given below show the movement of air (wind) in and between, high and low pressure regions. They use the map above (without Australia and New Zealandincluded).The balls represent parcels of air. Blue = colder air, orange = warmer air. The air warms up as it falls from above and cools down as it rises.Go to top |
Animation 1 |
| Noticehow the sinking air spirals outward in an anticlockwise direction, in the high pressure region (only in the southern hemisphere).In the low pressure region the rising air spirals inward, in a clockwisedirection (only in the southern hemisphere).
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Animation 2 |
| This animation shows how a small part of the air may flow across the isobars from high to low pressure. Go to top |...