2011118 What day is it today?
The calculation method of the number of nine: from the solstice in winter to the unhealed day in winter (the first unhealed day is called "crossing nine", which means the beginning of cold), every nine days is a "nine", the first nine days are called "one nine", the last nine days are called "two nine", and so on, to "nine nine nine nine" and "nine peach blossoms".
As the saying goes, "Summer solstice is three years old, and winter solstice is nine years old." . It is generally the coldest in April and September, which is the coldest period of the year; By the ninth five-year plan, the cold has disappeared and spring is getting warmer and warmer.
The mechanism of the number nine
During the winter solstice, the daytime is the shortest, the angle of direct sunlight on the ground is the smallest, and the sunshine intensity per unit area on the ground is also the smallest, so the ground gets the least solar heat every day, and the daily heat budget deficit on the ground has not reached the maximum. On the solstice after winter, although the day is growing day by day, the growth rate is very slow.
From winter to March 9, the average daily increase is only about one minute, and the direct angle between the sun and the ground increases slowly. The daily heat budget of the ground is still in a deficit state, so it continues to lose heat and the ground temperature continues to drop. The total heat budget deficit on the ground only reached the maximum during the "April 9" period, and the temperature was mainly affected by the ground temperature.
This resulted in the lowest temperature during "March 9th and April 9th". In addition, around March 9, the cold air mass in Siberia also developed to a very strong stage, and the frequent invasion of strong cold air is also one of the reasons for the low temperature.