Intertropical convergence zone

Japanese: 熱帯収束帯 - ねったいしゅうそくたい（英語表記）intertropical convergence zone

A convergence zone (→ front) formed in the tropical regions near the equator. It was formerly called the tropical front, equatorial front, equatorial convergence zone, or equatorial low pressure zone, but today it is generally called the ITC. It is often abbreviated as ITC or ITCZ. It is called the convergence zone because it is formed by the convergence of trade winds (wind direction difference) between the northern and southern hemispheres, without much temperature difference like the frontal zones in the mid- and high-latitudes. It is used to refer to the convective cloud line (cumulonimbus cloud) that surrounds the equator in a band-like shape based on observations by meteorological satellites. Even if the wind convergence is weak, the sea area with cumulonimbus clouds that occurs due to active convection activity caused by high sea water temperature is also called the ITCZ. In summer, it moves to both hemispheres depending on the season to create a convergence zone between the trade winds flowing in across the equator and the trade winds in the summer hemisphere. One notable phenomenon within the convergence zone is intraseasonal variation, in which the cyclone develops and disappears repeatedly as it moves eastward from the Indian Ocean region to the central equatorial Pacific Ocean in a cycle of 30 to 60 days. This phenomenon is said to be closely related to the strength of the monsoon and the El Niño phenomenon.

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

Japanese:

赤道付近の熱帯域に形成される収束帯（→前線）。かつては熱帯前線，赤道前線，赤道収束帯，赤道低圧帯とも呼ばれたが，今日では一般的に熱帯収束帯と呼ぶ。ITC，ITCZと略されることも多い。中・高緯度の前線帯のように気温差をあまり伴わず，南北両半球の貿易風の収束（風向差）によって形成されることから収束帯と呼ばれる。気象衛星の観測などから，赤道付近を帯状にとりまく対流雲列（積乱雲）に対して使用される。風の収束が弱くても，高い海水温による活発な対流活動等で発生する積乱雲群の海域なども，熱帯収束帯と呼ばれる。夏季には赤道を越えて流入する貿易風と夏半球側の貿易風との間に収束帯をつくるため，季節によって両半球へ移動する。収束帯内で注目すべき現象として 30～60日の周期でインド洋域から赤道中部太平洋域を東進しながら発達と消滅を繰り返す季節内変動といわれる現象があり，モンスーンの強弱やエルニーニョ現象などと深く関係しているといわれる。

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