The coldest solar term in sunshine

No. The temperature was the lowest on March 9th.

On the day of winter solstice, the northern hemisphere gets the least solar radiation, about 50% less than the southern hemisphere. Beijing's daylight saving time is only over 9 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".

Coldest:

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 the winter solstice to the "March 9" period, the average daily growth is only about one minute. At the same time, the angle between the direct angle of the sun and the ground is slowly increasing. 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 deficit of total heat balance on the ground only reaches the maximum in the season of March 9. Because the temperature is mainly affected by the ground temperature, it leads to the lowest temperature in March 9 (of course, this is not the case all over the country, but every year, depending on the region and age). 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.

Extended data

Winter solstice:

The winter solstice (the node of Gregorian calendar 65438+February 2 1-23) is one of the 24 solar terms in the Gregorian calendar, indicating the change of seasons. Fingers are the solstice in winter, that is, the sun runs to 270 degrees of the yellow meridian (the solstice in winter), and the solstice in winter marks the arrival of winter.

On the solstice of winter, the sun shines directly on the ground and reaches the southernmost tip of the year. The sun is almost directly on the tropic of Capricorn (also known as the winter solstice daily line), and the sun is most biased towards the northern hemisphere. Therefore, the winter solstice is the shortest day in the northern hemisphere, and the farther north, the shorter the day.

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 "three or nine days", the accumulated heat is the least, the temperature is the lowest, and 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. So it is said to be "cold in March", but "September 9" is already January and February in the summer calendar, and most parts of China have entered spring, so "September 9 is sunny".

Baidu encyclopedia-winter solstice

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