A meteorological term for a high pressure system. Anticyclones are areas of generally clear skies and stable weather conditions. They occur in a variety of sizes and modes of origin, and warm anticyclones are a semi-permanent feature of subtropical areas (eg the Azores and Hawaiian high pressure zones). A blocking anticyclone may persist for several weeks, travelling very slowly and diverting depressions around it. In the N hemisphere, surface winds blow in a clockwise direction out of an anticyclone; in the S hemisphere the direction is anticlockwise.
opposite to a cyclone) is a weather phenomenon in which there is a descending movement of the air and a relative increase in barometric pressure over the part of the earth's surface affected by it.Terminology
Confusion may be created by the fact that the term "subtropical anticyclone" is used by meteorologists in Australia in place of "extratropical anticyclone", which is the term that used in the United states. there are no separate or different types of warm dry air anticyclones being generated by the ITCZ.
Formation
All anticyclones are produced by dry air that settles to the surface of the earth and accumulates, forming air masses. The absence of aqueous vapor (water vapour) increases the density of air which means that each volumetric unit of dry air weighs more than the same volumetric unit of humid air at the same temperature, and vapour pressure.
Anticyclogenesis
Cool or cold dry air type
Cool or cold dry air settles onto land and forms shallow anticyclones or high-pressure cells which often move across the terrain and create fair weather with little cloudiness or precipitation, then dissipate and vanish after reaching the open sea. Rising air in them eventually descends to form anticyclones. The position of each anticyclone is at about the same place on the surface as it is the air far above the surface. NSIDC
Warm, dry air type
An anticyclone composed of warm dry air may be situated over much of the North Atlantic ocean during most of the year. The warm dry air type of anticyclone is tall and may be observed on weather charts above three miles (5km) in height.
The maximum sea-level pressure in this type of anticyclone is not very high.
Similar anticyclones that are built of warm dry air exist over other oceanic areas of the world, such as the South Atlantic ocean.
Structure
At the surface the air tends to flow outwards in all directions from the central area of high pressure, and is deflected on account of the earth's rotation (see Coriolis effect) so as to give a spiral movement. The rotation is caused by the movement of colder higher pressure air that is moving away from the poles towards the equator being affected by the rotation of the earth. Since the air in an anticyclone is descending, it becomes warmed and dried, and therefore transmits radiation freely whether from the sun to the earth or from the earth into space.
Anticyclones generally bring fair weather and clear skies as the dynamics of an anticyclone lead to downward vertical movement which suppresses convective activity and generally lowers the mean relative humidity, in contrast to the upward vertical movement in a cyclone. However as the anticyclone moves over the earth surface it may heat up locally, acquire water from the land or oceans or encounter warmer wet air.
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Evolution
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Motion
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Effects
In winter anticyclonic weather is characterized by clear air with periods of frost, causing fogs in towns and low-lying damp areas, and in summer by still cloudless days with gentle variable airs and fine weather.
Local geography may cause a range of localised weather phenomena specific to anticyclones, while the interaction of the different air masses, which occurs at weather fronts, may cause a range of weather events.
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Anticyclonic storms
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