It is the coldest climate on Earth, with low temperatures at high latitudes that make it impossible for trees to grow. It is located on the polar side of the subpolar climate, but in the Southern Hemisphere, there is almost no land at the corresponding latitude, so the subpolar climate does not exist, and the polar climate and temperate climates directly border each other. Near the poles, the sun is above the horizon all year round in summer, and a considerable amount of solar energy is used to melt snow and ice. However, the sun's altitude is low and the atmospheric layer it passes through is thick, so the actual amount of sunlight is not much. In winter, there is almost no daylight, so the temperature does not rise and it is very cold all day. Most of the precipitation is snow, and the total annual amount is extremely small. It is subdivided into snow and ice climates, which are covered with ice and snow all year round, such as Greenland and Antarctica, and tundra climates, where mosses and lichens can grow. In the Köppen climate classification, it refers to a climate with an average monthly temperature of less than 10°C in the warmest month, and 0°C is the border between tundra climates (Köppen ET climates) and snow and ice climates (EF climates). In addition, much of the cold region is permafrost, and the climate in this region is also called a permafrost climate. [Shuji Yamashita] [Reference items] | | | | | |Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
高緯度にあるため低温で樹木の生育が不可能な、地球上でもっとも寒冷な気候である。亜寒帯気候の極側に位置するが、南半球では対応する緯度にほとんど陸地がないために亜寒帯気候は存在せず、寒帯気候と温帯気候とが直接境を接している。極付近では夏季は一年中太陽が地平線上にあり、かなりの量の太陽エネルギーが氷雪の融解に使われる。しかし、太陽高度が低く、通過する大気層も厚いので、実際の日射量は多くはない。冬は昼の時間がほとんどないので気温は上昇せず、一日中非常に低温である。降水のほとんどが雪で、年総量はきわめて少ない。グリーンランドや南極大陸のように一年中氷や雪で覆われている氷雪気候と、コケ植物や地衣類が生育できるツンドラ気候に細分される。ケッペンの気候分類では最暖月の月平均気温10℃未満の気候をさし、0℃を、ツンドラ気候(ケッペンのET気候)と氷雪気候(EF気候)の境とした。また、寒帯地方の多くは永久凍土帯であり、この地域の気候を永久凍結気候ともよぶ。 [山下脩二] [参照項目] | | | | | |出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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