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High pressure area facts for kids

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High pressure symbol
The letter H is used to stand for a high pressure area.

A high pressure area (also called a high or high-pressure) is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment. In the northern hemisphere, winds within high pressure areas circulate outward and clockwise, whereas winds circulate outward and counter-clockwise (BE: anticlockwise) in the southern hemisphere. Regions of high pressure are alternatively referred to as anticyclones.

High pressure areas are generally associated with cooler, drier air as well as clearing skies due to their formation within areas of atmospheric subsidence, or areas of large scale air descent. The area of high pressure associated with the descending branch of the Hadley cell, known as the subtropical ridge, steer tropical waves and tropical cyclones across the ocean. The subtropical ridge also helps form the world's deserts. On english weather maps, high pressure centers are associated with the letter H. On spanish weather maps, high pressure centers are associated with the letter A, for alta.


Surface analysis
A surface weather analysis for the United States on October 21, 2006.

High pressure systems form due to downward motion through the troposphere. Preferred areas within a synoptic flow pattern in the mid to upper levels are on the western side of troughs. On weather maps, these areas show converging winds (isotachs), also known as confluence, or converging height lines near or above the level of non-divergence, which is near the 500 hPa pressure surface about midway up through the troposphere.

High pressure systems are alternatively referred to as anticyclones. On weather maps, high pressure centers are associated with the letter H in english, or A in spanish, where alta is the word for high within the isobar with the highest pressure value. On constant pressure upper level charts, it is located within the highest height line contour.

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