Why is there first frost in autumn?

The rotation of seasons is like this every year, and it is never late. Autumn becomes autumn and winter. In frost and snow season, autumn leaves fall, and autumn colors pass by. Snow and frost always come in a hurry and surprise. This tells us that the year is coming to an end and everything is back to its original state. In autumn and winter on Beishanliang, the first frost comes, and several old elms on campus seem to be covered with frost overnight.

On the way of pedestrians, there is a sense of harvest inadvertently. Cold dew comes early, beginning of winter comes late, and the first frost season always brings back childhood memories. There were no out-of-season vegetables and fruits in those days. Before the first frost, corn stalks and potatoes look like alfalfa grass, and they are placed on the roof as supplementary feed for cattle and sheep in winter. Vegetables, fruits, etc. They are all hidden in the cellar, as a supplementary food for family members, and are usually eaten in the spring of next year.

Extended data:

The arrival of winter solstice solar terms marks the beginning of winter. On this day, although the northern hemisphere received the least solar radiation, it was about 50% less than the southern hemisphere. However, this is not the coldest time, so-called "March 9, April 9 cold." This is because there is atmosphere and water on the surface of the earth, which can store heat, not "save or lose" but "accumulate heat"

Therefore, the weather is usually not very cold before the winter solstice. 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". On the day of "March 9 and April 9", the accumulated heat is the least, the temperature is the lowest, and the weather is getting colder and colder.