What are the coldest days of the year?
In people's perception, "March 9th" is the coldest time, that is, starting from March 9th, it enters the coldest stage among the nine cold days. Sanjiu days refers to the third "nine days" counting from the winter solstice, which is the 19th to 27th days after the winter solstice.
During the winter solstice, the day is the shortest, the angle between the direct sunlight angle and the ground is the smallest, and the intensity of sunlight per unit area of the ground is the smallest. Therefore, the ground receives the least solar heat every day, and the daily heat budget deficit on the ground has not yet reached maximum value.
After the winter solstice, although the days are increasing day by day, the growth rate is very slow. From the winter solstice to the "March 9th" period, the average daily growth is only about one minute. At the same time, the direct angle of the sun is different from that of the ground. The included angle also increases slowly. The daily heat budget of the ground is still in deficit, so it continues to lose heat and the ground temperature continues to drop.
The total ground heat budget deficit reaches its maximum value only during the "March 9th" season. Since the temperature of the air is mainly affected by the ground temperature, this leads to the lowest temperature in the "March 9th" season. In addition, around the "March 9th" season, the cold air mass in Siberia has also developed to an extremely strong stage, and the frequent intrusion of strong cold air has also caused One of the reasons for the low temperature.
Extended information:
Extreme "low temperature" in China:
The Bendu River in Daxinganling, Inner Mongolia Autonomous Region, China, observed -50.1 on January 16, 1922 The temperature is ℃, which is the lowest value in the temperature record before the founding of New China. ?
After the founding of the People’s Republic of China, the Fuyun Weather Station in northern Xinjiang broke the record for free crossing of the river for the first time on January 20, 1960 with a low temperature of -50.7°C, and then again on January 21 with a low temperature of -51.5°C. ℃ once again set a new national record.
The northernmost weather station in China, the Mohe Meteorological Station in Heilongjiang Province, measured a temperature of -50.9°C in the early morning of December 27, 1968.
On February 13, 1969, Mohe once again set the extreme lowest temperature record in China's existing meteorological data - -52.3℃.
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