What does the weather mean on March 9?

As a method to record the cold winter, China folks divide the winter to 8 1 day in the future into 9 stages, each of which lasts for 9 days, which is called "Winter 99", which is often called "Nine Cold". Among them, the solstice from 0/9 to 27 days after beginning of winter every year is called "Sanjiu".

Zhao Zhi Heng, director of Tianjin Astronomical Society, said that from the astronomical point of view, the degree of warmth and coldness in a place is related to the altitude angle of the sun at noon. On the day of winter solstice, the height angle of the sun is the lowest, and Beijing is only 26 degrees. The height angle of the sun is small, and the degree of oblique sunlight is large. It reaches the ground through the thick atmosphere, and a large part of the heat is absorbed by the atmosphere.

On the day of winter solstice, the northern hemisphere gets the least sunshine, 50% less than the southern hemisphere. Beijing's daylight saving time is only nine hours. But this day is the first day of counting nine, and it is not the coldest time. This is because there is atmosphere and water vapor on the surface of the earth, which can store heat, not "save or lose" but "accumulate heat".

From winter to the future, although the solar altitude angle gradually increases, it is a slow recovery process, and the heat lost every day is still greater than the heat received, showing a situation of "making ends meet".

In the "March 9th" weather, the accumulated heat is the least and the temperature is the lowest, so the weather is getting colder and colder. If there is the influence of cold air at this time, the weather will be even colder. After this "cold front", the weather will gradually get warmer.