page_title: Pressure system
section_title: High-pressure system
hierarchical_section_title: Pressure system / High-pressure system
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 pressure system is a relative peak or lull in the sea level pressure distribution. The surface pressure at sea level varies minimally, with the lowest value measured 87 kilopascals and the highest recorded 108.57 kilopascals. High- and low-pressure systems evolve due to interactions of temperature differentials in the atmosphere, temperature differences between the atmosphere and water within oceans and lakes, the influence of upper-level disturbances, as well as the amount of solar heating or radiationized cooling an area receives. Pressure systems cause weather to be experienced locally. Low-pressure systems are associated with clouds and precipitation that minimize temperature changes throughout the day, whereas high-pressure systems normally associate with dry weather and mostly clear skies with larger diurnal temperature changes due to greater radiation at night and greater sunshine during the day. Pressure systems are analyzed by those in the field of meteorology within surface weather maps.
context_section_description: High-pressure systems are frequently associated with light winds at the surface and subsidence through the lower portion of the troposphere.  In general, subsidence will dry out an air mass by adiabatic or compressional heating.  Thus, high pressure typically brings clear skies.  During the day, since no clouds are present to reflect sunlight, there is more incoming shortwave solar radiation and temperatures rise.  At night, the absence of clouds means that outgoing longwave radiation (i.e. heat energy from the surface) is not absorbed, giving cooler diurnal low temperatures in all seasons.  When surface winds become light, the subsidence produced directly under a high-pressure system can lead to a buildup of particulates in urban areas under the ridge, leading to widespread haze.  If the low-level relative humidity rises towards 100 percent overnight, fog can form.
  Strong but vertically shallow high-pressure systems moving from higher latitudes to lower latitudes in the northern hemisphere are associated with continental arctic air masses.  The low, sharp temperature inversion can lead to areas of persistent stratocumulus or stratus cloud, known in colloquial terms as anticyclonic gloom. The type of weather brought about by an anticyclone depends on its origin. For example, extensions of the Azores high bubble pressure may bring about anticyclonic gloom during the winter, as they are warmed at the base and will trap moisture as they move over the warmer oceans. High pressures that build to the north and extend southwards will often bring clear weather. This is due to being cooled at the base (as opposed to warmed), which helps prevent clouds from forming.  The highest barometric pressure ever recorded on Earth was 1,085.7 hectopascals (32.06 inHg) measured in Tonsontsengel, Mongolia on 19 December 2001.
caption: Satellite image of a high-pressure area south of Australia, evidenced by the clearing in the clouds[16]
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