page_title: High-pressure area
hierarchical_section_title: High-pressure area
caption_attribution_description: English: The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired this view of a hole in a cloud formation at 3:00 p.m. local time (05:00 Universal Time) on June 5, 2012. The weather system over the Great Australian Bight cut out the oval-shaped hole from a blanket of marine stratocumulus clouds in Southern Australia at Great Australian Bight. Satellite loop at the the time the image above was taken, showed the Anticyclone was spinning anticlockwise, as it is in the Southern Hemisphere. Sea-level pressure maps published by the Australian Bureau of Meteorology on June 5 showed that the shape of the cloud hole matched the shape of the high-pressure area. However, the center of high pressure and the cloud hole didn't match precisely; the center of the high was near the western edge of the clear area, about 100 kilometers from the cloud edge. The area within the spot, which marks the High Pressure area, marks the boundary of 1036hpa pressure. The center of the spot was 1039hpa at the time the image was taken-more proof that this is a High Pressure area-http://earthobservatory.nasa.gov/IOTD/view.php?id=78208 The cloud hole, with a diameter that stretched as far as 1,000 kilometers (620 miles) across, was caused by sinking air associated with an area of high pressure near the surface. Globally, the average sea-level pressure is about 1013 millibars; at the center of this high, pressures topped 1,040 millibars.
context_page_description: A high-pressure area, high, or anticyclone, is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment.
  Winds within high-pressure areas flow outward from the higher pressure areas near their centers towards the lower pressure areas further from their centers. Gravity adds to the forces causing this general movement, because the higher pressure compresses the column of air near the center of the area into greater density – and so greater weight compared to lower pressure, lower density, and lower weight of the air outside the center.
  However, because the planet is rotating, the air flow from center to periphery is not direct, but is twisted due to the Coriolis effect. This is an apparent, but fictitious, force that arises when an observer is in a rotating reference frame, due to the conservation of angular momentum of the air as it moves towards or away from the Earth's axis of rotation. Viewed from above this twist in wind direction is in the opposite direction as the rotation of the planet.
context_section_description: A high-pressure area, high, or anticyclone, is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment.
  Winds within high-pressure areas flow outward from the higher pressure areas near their centers towards the lower pressure areas further from their centers. Gravity adds to the forces causing this general movement, because the higher pressure compresses the column of air near the center of the area into greater density – and so greater weight compared to lower pressure, lower density, and lower weight of the air outside the center.
  However, because the planet is rotating, the air flow from center to periphery is not direct, but is twisted due to the Coriolis effect. This is an apparent, but fictitious, force that arises when an observer is in a rotating reference frame, due to the conservation of angular momentum of the air as it moves towards or away from the Earth's axis of rotation. Viewed from above this twist in wind direction is in the opposite direction as the rotation of the planet.
  The strongest high-pressure areas are associated with cold air masses which push away out of polar regions during the winter when there is less sun to warm neighboring regions. These Highs change character and weaken once they move further over relatively warmer water bodies.
  Somewhat weaker but more common are high-pressure areas caused by atmospheric subsidence, that is, areas where large masses of cooler, drier air descend from an elevation of 8 to 15 km after the lower temperatures have precipitated out the water vapor.
  Many of the features of Highs may be understood in context of middle- or meso-scale and relatively enduring dynamics of a planet's atmospheric circulation. For example, massive atmospheric subsidences occur as part of the descending branches of Ferrel cells and Hadley cells. Hadley cells help form the subtropical ridge, steer tropical waves and tropical cyclones across the ocean and is strongest during the summer. The subtropical ridge also helps form most of the world's deserts.
  On English-language weather maps, high-pressure centers are identified by the letter H. Weather maps in other languages may use different letters or symbols.
caption: Satellite image of an unusual high-pressure area south of Australia, evidenced by the clearing in the clouds[1]
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