Subtropical high pressure - Anetai high pressure

A type of high pressure system that exists almost constantly in the latitude band of about 20 to 40 degrees in both the northern and southern hemispheres. It is thought that the cause of this is the accumulation of air moving from the equator to the subtropics due to the vertical circulation (large-scale convection) of the atmospheric general circulation scale, which causes updrafts in the equatorial zone and downdrafts in the subtropics, and increases the pressure in the lower layers. It mainly appears in a line from east to west over the ocean, and the belt of high pressure or pressure ridge is called the subtropical high pressure belt. Structurally, it is a tall warm high pressure system. It is dominant in the summer, and appears at higher latitudes in the summer. Individual subtropical high pressure systems are named after the ocean area where they exist, such as the North Pacific high pressure system, the North Atlantic high pressure system, and after the names of representative islands within the zone, such as the Ogasawara high pressure system, the Hawaii high pressure system, the Azores high pressure system, and the Bermuda high pressure system. The clear skies and heat of midsummer in Japan are brought about by the subtropical high pressure system (Ogasawara high pressure system).

[Atsushi Kurashima]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

南北両半球の20度から40度ぐらいの緯度帯にほぼ定常的に存在する高気圧。成因としては、赤道地帯で上昇流、亜熱帯で下降流となる大気大循環規模の垂直循環（大規模な対流）によって、赤道上空から亜熱帯に向かう空気が亜熱帯上空で蓄積、下層の気圧を高めるためと考えられる。主として海洋上に東西に並んで現れるが、その一連の高気圧または気圧の尾根のベルトを亜熱帯高圧帯とよぶ。構造的には背の高い温暖高気圧である。夏季に優勢で、出現緯度も夏季のほうが高い。個々の亜熱帯高気圧は、それが存在する海域により北太平洋高気圧、北大西洋高気圧、また圏内の代表的な島の名前から、小笠原高気圧(おがさわらこうきあつ)、ハワイ高気圧、アゾレス高気圧、バーミューダ高気圧などと名づけられる。日本の盛夏の晴天と暑さは亜熱帯高気圧（小笠原高気圧）によってもたらされる。

［倉嶋　厚］

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