Autumn, also known as autumn, is the third season throughout the year, and the transition season from summer to winter is from 9 to 1 1 month in the northern hemisphere, from March to May in the southern hemisphere, and from autumnal equinox to winter solstice in astronomy. Meteorologists study phenology according to the following criteria: after the heat, the five-day average temperature is stable below 22 degrees, which means it enters autumn, and it ends when it is below 10 degrees.

There are six solar terms in autumn, namely beginning of autumn, Chushu, Bailu, Autumnal Equinox, Hanlu and first frost.

The temperature in autumn will gradually drop, but it is generally slower than that in winter. Due to the difference of wet and dry conditions, cold and rainy weather conditions or dry and cool weather conditions will appear in different regions. In the cold late autumn, due to the large temperature difference between day and night, the water vapor transpiration during the day will condense at night, either for dew or frost.

In autumn, the direct point of the sun gradually moves south from the northern hemisphere, crosses the equator after the autumnal equinox, and the sun directly shines in the southern hemisphere. From the perspective of the northern hemisphere, the angle of the sun gradually becomes lower, and the gap between day and night becomes smaller. At the autumnal equinox, day and night are equal in length. In autumn, the distance between the earth and the sun approaches from far away. Seen from the ecliptic plane, the sun is located on the background of Leo, Virgo and Libra.

Extended data beginning of autumn is the 13 solar term among the 24 solar terms. On August 7th or 8th every year, beginning of autumn is regarded as the time when the sun reaches the longitude135. "Autumn" means that the summer is cool, which means the beginning of autumn. But in beginning of autumn, the weather in Jianghuai area is still very hot. According to the standard of dividing seasons by average temperature, it must be that the average temperature of 5 days is below 22℃ to be considered as autumn.

According to this standard, the Jianghuai area generally enters autumn in the middle and late September. After beginning of autumn, although the summer heat is hard to disappear for a while, there is still the afterglow of "autumn tiger", but the general trend is that the weather is getting cooler. The daily range of temperature is gradually obvious, which is often very hot during the day and cool at night.

Baidu Encyclopedia-Autumn