What happened to nature on the vernal equinox?

The vernal equinox is one of the solar terms reflecting the changes of the four seasons. In ancient China, beginning of spring, Changxia, beginning of autumn and beginning of winter were used to express solar terms.

It indicates the beginning of the four seasons. The vernal equinox, summer solstice, autumn equinox and winter solstice are in the middle of each season. On the vernal equinox, the sun shines directly on the equator, and the time between day and night is equal all over the earth. Therefore, the ancient vernal equinox and autumnal equinox are also called "equinox", and there is a folk proverb that "vernal equinox and autumnal equinox are equally divided day and night". After the vernal equinox, the overwintering crops in most parts of China entered the spring growth stage. There is an agricultural proverb in Central China, "Wheat starts at the vernal equinox, and every moment is worth a thousand dollars". The temperature in all parts of Sichuan Province continues to rise, but it is generally not as fast as the rainfall to the vernal equinox. In late March, the average temperature in the north of the basin was mostly 13℃ to 15℃, and in the south of the basin was mostly 15℃ to 16℃. Most of the plateau has been melted by snow, and the ten-day average temperature is about 5℃ to 10℃. The Jinsha River and Anning River basins in southwest Sichuan have the highest temperatures, with an average of 18℃ to 20℃. Except in marginal mountainous areas, the average daily temperature in the basin has steadily increased to above 65438 02℃ in the past seven or eight years, which is beneficial to planting crops such as rice and corn, and is also very suitable for afforestation. However, before and after the vernal equinox, strong cold air often invades the basin, and the temperature drops obviously, and the lowest temperature can be as low as 5℃. Sometimes a small stream of cold air comes one after another, forming a low temperature and rainy weather that lasts for several days, which is not good for agricultural production. According to this feature, we should make full use of the fourth solar term in a year. At this time, the day and night are equally divided, that is, the time when the sun is on the ecliptic is from 0 to 15 (about 15.2 days), from March 20th (or 2 1) to April 4th (or 5th) every year. At this time, the direct point of the sun moved from the equator to 5 57 ′ n, which in a narrow sense refers to the beginning of the vernal equinox, depending on the moment when the sun passes through the 0 intersection point (ascending intersection point) of the equator on the celestial sphere; That is, March 20th (or 2 1). Because this moment coincides with the vernal equinox, this intersection is also called the vernal equinox. The vernal equinox and autumnal equinox are collectively called vernal equinox.

The ancient vernal equinox is divided into three stages: "wait for the dark sky to come, wait for the thunder to start, and wait for the electricity to start." In other words, after the vernal equinox, swallows will fly from the south, and when it rains, the sky will thunder and lightning. "Twenty-four solar terms" has: "In mid-February, half a minute is half of 90 days, so it is called half." "Spring and Autumn Story? "Yin and Yang in and out" has: "In the Spring Festival, Yin and Yang are also half-phase, and it is good to be hot and cold day and night. "On this day, the sun points directly at the equator, almost as long as day and night in the world. After that, the position of direct sunlight moved northward, with long days and short nights in the northern hemisphere and short days and long nights in the southern hemisphere. According to astronomy, spring begins in spring.

During the vernal equinox, most of northwest China, northern North China and northeast China are still in the transitional stage of winter and spring, with many sunny days and windy days, and it is warm and cold at first sight. According to the statistics of weather in this area in recent years, April is the most, followed by March. The vernal equinox is 15 days, that is, from the end of March to the beginning of April. In these areas, dust blown by strong winds and floating dust at high altitude, especially the air pollution caused by dust storms, have always been concerned by everyone and become a hot topic for some time. Perhaps this is also the culprit of smog.