What solar terms are frozen in Beijing?

The winter solstice is the 22nd solar term among the 24 solar terms in the lunar calendar, and it is the shortest day and the longest night in the northern hemisphere. After this day, the days will get longer and the nights will get shorter. The winter solstice in 2020 will be February 2 1 65438, but the temperature will not be too cold. People can't help asking, what is the coldest day in winter in a year?

There is a folk song: "1929 Don't shoot; Walking on the ice in 3949; See the willows by the river in May and June, the frozen river opens in July and September, the geese return in August and September, and the cattle are ploughed in September and September. "

Every winter, there is strong cold air heading south, causing sudden cooling, which is also the lowest temperature in a year. This folk song shows the ups and downs of temperature. We often hear the words "the cold is in March 9th, the heat is in the middle, count nine winters, March 9th, and the twelfth month of winter". People in China have the habit of counting to nine. Starting from the winter solstice, every nine days count as nine days. Once winter comes to 18 days from 36 days to 54 days in the future, willows along the river will sprout new buds and the climate will get warmer; From winter to 54 to 72 days in the future, the frozen river began to melt, and geese flew back to the north from the south; 72-8 1 winter solstice and the days after that, the weather will be completely warm when spring ploughing is ready.

Why is this happening? Why is today the coldest day? Due to the increase of the direct angle of the sun and the slow growth of sunshine time, the daily heat loss of the earth is still greater than the heat received from winter to the future. In the "three or nine days", the accumulated heat reaches the lowest point, which is the coldest time; Beginning of winter began to "harvest everything". When it reached its extreme, winter arrived, so it was called the winter solstice solar term. In addition, the cold air mass in Siberia also developed to a very strong stage around March 9, and gradually weakened with the increase of sunshine time in the later period, which is also the reason why it may be the coldest around March 9.

Therefore, the annual "March 9th" is the coldest time of the year.