rainy season


July 5, 2022

The rainy season is a unique meteorological phenomenon found in a wide range of East Asia, including Japan excluding Hokkaido and the Ogasawara Islands, the southern part of the Korean Peninsula, the coastal areas from the southern part of China to the Changjiang River, and Taiwan. The cloudy and rainy season that comes from March to July. It is a kind of rainy season.

Rainy season in the four seasons of East Asia

When the climatological seasonal changes are compared with the world, the changes in the five seasons with the rainy season added to spring, summer, autumn and winter in East Asia, and the changes in the six seasons with the additional autumn rain in Japan are clearly visible. In East Asia, extratropical cyclones and mobile highs alternate in spring and autumn, and the weather changes periodically. On the other hand, in midsummer, it is covered with hot and humid air mass under the influence of subtropical high pressure (Pacific high pressure). Then, between spring and midsummer, and between midsummer and autumn, the rainy season occurs due to the stagnation of fronts from the eastern part of mainland China to the eastern offshore of Japan. Among them, the rainy season between spring and midsummer is the rainy season, and the rainy season between midsummer and autumn is the autumn rain. The rainy season is clear throughout East Asia, while the autumn rain is weak in the direction of mainland China and clear in the direction of the Japanese archipelago. In addition, as a breakdown of the rainy season between midsummer and autumn, the rain caused by typhoons has a considerable influence. The beginning of the rainy season is called the rainy season or the beginning of the summer (early summer), which is the end of spring and the beginning of summer (early summer) in terms of social conventions and meteorology. In addition, one of the miscellaneous clauses in Japan is Iriume (around June 11th), which is referred to as Iriume on the calendar, but this is a guideline for the time of rice planting that requires water. In addition, the end of the rainy season is called the end of the rainy season or Shutsubai, and this is often the arrival of full-scale summer (midsummer). In most areas, meteorological authorities have announced the start of the rainy season and the end of the rainy season. The period of the rainy season is usually about one to one and a half months. In the rainy season, precipitation is about 500 mm in Kyushu, which is about one-fourth of the year, and in Kanto and Tokai, it is about 300 mm, which is about one-fifth of the year. In western Japan, the rainy season has more rainfall than in autumn, but in eastern Japan, on the contrary, there is more rainfall (with the contribution of typhoons). The time of the rainy season and the amount of rainfall may fluctuate greatly depending on the year. For example, it may rain only about 150 mm, or the end of the rainy season may be delayed by two weeks from the normal year. In such years, the summer weather is not good and meteorological disasters are likely to occur, such as intense heat and light rain, and cold summer and heavy rain. East Asia is located at mid-latitudes. It is possible that the climate will be dry under the influence of subtropical high pressure, such as in the Middle East at the same latitude, but the eastern coast of the continent tends to have a lot of rain because it becomes the margin of the subtropical high pressure that covers the ocean in summer. .. This is the same on the east coast of the North American continent, but in Kyushu, the annual rainfall is about 2,000 mm, which is as much as the rainfall in the tropical convergence zone. The contribution of the rainy season and autumn rain to this abundant rainfall is large. One of the factors that cause a large amount of rainfall in the rainy season is that it is influenced by the hot and humid Asian monsoon that connects India to Southeast Asia. Occasionally, the rainy season is described as "raining slowly" and "rainy season and cloudy weather continue". This is correct in eastern Japan, but not so much in western Japan. This is because there are regional differences in the way the rainy season rains. Especially in western Japan and China (near the middle and lower reaches of the Yangtze River), water called a cloud cluster where cumulonimbus clouds gather.