Types of Anti-Cyclones
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. The types of anticyclones display different patterns of movement.
High-latitudes maritime type
In the months of winter, many strong cyclones appear at high latitudes. Rising air in them eventually descends to form anticyclones. Tall anticyclones appear at some places each year during the coldest months. They may exceed 35,000 feet or 10,200 meters in height. The position of each anticyclone is at about the same place on the surface as it is far above the surface. The sea-level pressure may exceed 1040 millibars (hectopascals) (hPa) (SI). They tend to linger close to the place at which they had appeared.
The Denmark Strait along the east coast of Greenland is a place where they appear, often, during the winter. They form part of the North Atlantic Oscillation that affects the weather much. The Beaufort Sea is an arm of the Arctic Ocean that exists north of northwestern Canada. An anticyclone called the Arctic High or the Beaufort High forms there.
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 warm dry air type of anticyclone is usually described as being semipermanent. Frontal activity is not associated with it. Transoceanic in extent, in Europe it is called the Azores High, and in the United States it is known by the name Bermuda High.
Since it has a tropical origin, its most proper name is extratropical anticyclone(but see the last paragraph, below). It has a characteristic "vertical displacement" that shifts its center away from its surface position towards the equator and westwards, too. Far above the surface of the North Atlantic ocean at a height of 3-4 miles (5-7km), the center of the high-pressure cell may be seen about 3,000 miles (5,000km) southwestwards of its surface position (which is in the general vicinity of the Azores Islands).
The maximum sea-level pressure in this type of anticyclone is not very high. It may reach, perhaps, 1025 millibars (hectopascals) or thereabouts during the summertime, which is a mere twelve millibars above the average sea-level pressure of 1013 millibars.
Similar anticyclones that are built of warm dry air exist over other oceanic areas of the world, such as the South Atlantic ocean. The anticyclone that is located there is practically a mirror-image of the anticyclone that is located over the North Atlantic ocean. Its "vertical displacement" is also towards the equator and westwards, too. The warm dry air is continually being produced in the Intertropical convergence zone by thunderstorms.
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. Except for the wordage, there is no difference; there are no separate or different types of warm dry air anticyclones being generated by the ITCZ. Both extratropical cyclones and extratropical anticyclones are seen in the Northern Hemisphere, year-round.
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