On the other hand, the spring equinox has a fixed period of time every year. According to the calculation formula, the time of the spring equinox in 2019 is 05:58:20 on March 21.
Spring equinox time of 2019: Thursday, March 21, 2019 (February 15, year of the pig)
Calculation formula:
[Y*D+C]-L
Interpretation of the formula: multiply the last two digits of the year by 0.2422 plus 20.646, take the integer minus the number of leap years, and the C value of the spring equinox in the 21st century is 20.646.
For example, the date of the equinox in 2092 = [92 & times; 0.2422 + 20.646] - [92 / 4] = 42-23 = 19, and March 19 is the vernal equinox.
Exception: calculation results in 2084 plus 1 day.
According to the collection of the seventy-two orders of the month: "in the middle of February, there are half points, and this is the half of the ninety days, so it is called the division. In addition, it is said in the first and second chapters of the spring and Autumn Annals: in the vernal equinox, yin and yang are in half phase, so the cold and heat are even day and night. According to Li Yi in the history of the Ming Dynasty, the point where the yellow and the red intersect, the sun goes here, and the day and night are divided equally. Therefore, the meaning of vernal equinox is: first, the day and night of a day are equally divided, each of which is 12 hours; second, in ancient times, from the beginning of spring to the beginning of summer, the vernal equinox is equal to the spring in the three months of spring.
In ancient China, the vernal equinox was divided into three periods: the first was the arrival of yuanniao, the second was the sound of thunder, and the third was the beginning of electricity. That is to say, after the vernal equinox, swallows fly from the south, and when it rains, the sky will thunder and send out lightning.
Climatic characteristics of vernal equinox
Sunlight: on the vernal equinox, the sun is almost directly at the equator of the earth, and the length of day and night is almost equal all over the world. After the vernal equinox, the direct point of the sun begins to enter the northern hemisphere, and the days begin to lengthen and the nights begin to shorten all over the northern hemisphere. Vernal equinox is an important solar term. It not only has astronomical significance: the northern and southern hemispheres equinox, but also has obvious climatic characteristics. At the vernal equinox, except for the Qinghai Tibet Plateau, Northeast China, Northwest China and northern North China, China has entered a beautiful spring. On the vast land of Liaoning, willows are green, yingfeicao is long, wheat is jointing, and rape is fragrant.
Atmospheric pressure: during the spring equinox solar term, the East Asian trough is obviously weakened, and the activity of the trough ridge in the westerly belt is obviously increased. There are low pressure activities and cyclone development from Mongolia to Northeast China. The movement of low pressure leads the cold air to the south, and there are more gales and sand blowing weather in the north. When the long wave trough moves eastward and is affected by the convergence of cold and warm air masses, there will be continuous rain and cold weather in late spring.
Temperature and precipitation: during the spring equinox, the daily average temperature in all parts of China rises steadily above 0 ℃ except for the alpine mountain areas where winter is the whole year and the area to the north of the north latitude 45 DEG. At this time, the severe cold had passed away, and the temperature rose rapidly, especially in North China and Huanghuai Plain. The daily average temperature rose to more than 10 ℃ at the same time as the rainy Jiangnan area along the river, and entered the bright spring. On the vast land, willow green shore, warbler flying grass, wheat jointing, rape flower fragrance, peach red, plum white, welcome spring yellow, and South China is a school of late spring scene. According to the climate law, the precipitation in the south of the Yangtze River increased rapidly and entered the spring 'Peach Blossom flood' period. In the vast areas of northeast, North and Northwest China where the spring rain is as expensive as oil, the precipitation is still very little, and resisting the threat of spring drought is the main problem in agricultural production.