migratory (traveling) anticyclone

Japanese: 移動性高気圧 - いどうせいこうきあつ（英語表記）migratory (traveling) anticyclone

A moving high pressure system. There are two types of high pressure systems: migratory high pressure systems, which are paired with low pressure systems, and migratory high pressure systems caused by the inundation of polar air masses. The former are more common in spring and autumn around Japan, while the latter are in winter. The shape of a migratory high pressure system is close to a circle or ellipse on the ground, but not as round as a typhoon. Its diameter is about 500 to 2000 km, with an average of 1000 km. The pressure gradient is weaker toward the center, and the wind speed increases almost in proportion to the distance from the center. In a migratory high pressure system, the wind is weak, and clouds are less likely to form due to downdrafts, so the weather is good and the amount of water vapor is small. As a result, radiation is significant at night, and it becomes significantly cold near the ground at dawn, so late frosts can be seen in spring. Clouds appear soon after the center passes, and the weather often deteriorates. In the vicinity of Japan, they are carried by the westerly winds, so they often move east at a speed of about 40 km per hour. A migratory high pressure system is followed by a low pressure system, and then another high pressure system appears. This cycle usually lasts 3 to 4 days. The route of the migratory high pressure system often passes through northern Japan or along the Pacific coast, and has its maximum at latitudes of around 28° and 38°, which correspond to the positions of the subtropical jet stream and the polar jet stream.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

移動する高気圧。低気圧と対をなす移動性高気圧と極気団の氾濫による移動性高気圧がある。日本付近に春と秋によく現れるのは前者で，後者は冬に現れる。移動性高気圧の形は地上では円または楕円に近いが，台風ほど丸くはない。直径は 500～2000kmほどで，平均 1000km。気圧傾度は中心ほど弱く，風速は中心からの距離にほぼ比例して強くなる。移動性高気圧の中では風が弱く，下降気流により雲ができにくいため天気がよく，水蒸気の量が少ない。このため夜間の放射が著しく，地面付近では明け方著しく冷えるため，春には晩霜をみることがある。中心が通過するとまもなく雲が出て，天気が崩れることが多い。日本付近では偏西風に流されるため毎時 40kmくらいの速さで東に移動することが多い。移動性高気圧のあとには低気圧が続き，そのあとまた高気圧が現れる。この周期は 3～4日のことが多い。移動性高気圧の経路は日本北部を通る場合と，太平洋沿岸を通る場合が多く，緯度では 28°付近と 38°付近に極大がある。これは亜熱帯ジェット気流と寒帯ジェット気流の位置に対応する。

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