dàhán.
Introduction to solar terms:
Dahan is the last solar term among the twenty-four solar terms. The sun reaches 300 longitude on January 20-21 of the Gregorian calendar every year. ° is "big cold". "Shishi Tongkao·Tianshi" quoted from "Sanliyi Zong" and explained: "The big cold is the middle one, and the upper shape is better than the minor cold, so it is called big... The cold air is the reverse extreme, so it is called big cold." Extreme refers to the coldness of the great cold.
This season falls between March and April, when cold waves frequently move southward. It is the coldest season of the year and the period with the least rain. Folk proverb goes: "Small cold and big cold are cold when there is no wind." Dahan means that the weather is extremely cold. It is a season when vitality is latent and everything is dormant.
Although the winter solstice is the time when the sun is at its lowest in the northern hemisphere, the coldest time of the year is the minor cold and major cold periods after the winter solstice, especially the major cold period.
This is because after the winter solstice, the direct point of the sun will gradually move northward, but for a period of time thereafter, the direct point of the sun will always be in the southern hemisphere, and the heat in the northern hemisphere will always be lost. , the heat absorbed during the day is still less than the heat released at night, so after the winter solstice, the temperature in the northern hemisphere continues to decrease, and the temperature drops to the lowest during the Great Cold period.
Because China has a vast territory and a large span from north to south, there are great differences in climate between the north and south. According to China's long-term meteorological records, there is no mild cold in the Great Cold solar term in the north; but for some coastal areas in the south, the coldest is during the Great Cold solar term.