Is the vernal equinox solar term of 202 1 equal to day and night? Hydrometeorological characteristics?

The vernal equinox is an important solar term in spring. With the continuous development of time, the vernal equinox solar terms have formed many cultures. So, is the vernal equinox solar term 202 1 equal to day and night? What are the hydrometeorological characteristics of the vernal equinox solar terms?

Does 202 1 vernal equinox solar terms equal day and night? Yes

The vernal equinox is divided equally between day and night, and the direct point of the sun at the vernal equinox is above the equator, so the time between day and night at the vernal equinox is similar. The alternation of day and night is produced by the rotation of the earth. Because the earth is not luminous and opaque, at the same time, the sun can only illuminate half of the earth, the illuminated hemisphere is daytime, the unlighted hemisphere is night, and the earth rotates day and night. The dividing line between day and night is called the terminator line. Spring equinox solar terms, the sun reaches the yellow meridian 0? (Above the equator), the sun points right at the equator. At this time, the terminator line passes through the north and south poles and coincides with the meridian of the earth, dividing all latitudes into two parts, half in the day hemisphere and the other half in the night hemisphere, so the day and night around the world are almost equal.

Hydrometeorological characteristics of vernal equinox

aeolian sand

During the vernal equinox, the northwest, the northern part of North China and most of the northeast are still in the transitional stage from winter to spring, with sunny and windy days, and it is warm and cold at first sight. According to the statistics of dusty weather in recent years, April is the most frequent, followed by March, and 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 from high altitude, especially the air pollution caused by dust storms, have always been the focus of attention and become a hot topic for some time.

Low temperature and humid weather

At the vernal equinox, cold air constantly invades the south of China, and there will be cold weather in spring with low temperature. At this time, the continuous rain will have a great impact on crops. If the average temperature is lower than 10 12℃ for more than 5-7 days, it may cause serious rice seedling rot. Because rice and cotton are both thermophilic crops, when the temperature is above 10 12 and the minimum temperature in sunny days is above 5℃, it will be beneficial to all seedlings. Conversely, if there is low temperature and rainy weather, you can imagine. First frost is the product of cold wave and strong cold air in spring. In the case of warmer climate, cold waves are relatively rare, but we should not be careless.

Pre-flood season in southern China

There are two periods of concentrated rainfall in South China, one is the first flood season in April, and the other is the second flood season formed by typhoon rainfall in July. The first flood season begins in early April and reaches its peak in mid-May, with an average of 20 rainstorms per year, with the most in June, accounting for more than half of the total rainstorms. It lasts for a long time and the rain is fierce. Because the vernal equinox only touches the beginning of the flood season, I won't go into details here.