Can the second solar term "rain" in the twenty-four solar terms be called "cooling"?
In dry air, people's temperature equilibrium state (that is, feeling neither cold nor hot) is about 27 degrees Celsius. If the humidity is higher, it will be at least about 24 degrees. If the average temperature is kept at this temperature, it is within the summer range according to the waiting temperature method. In other words, if the waiting temperature method is used, all three seasons should be considered "cold". From this point of view, for the people in the central plains of the Yellow River, the average temperature of a day began to drop below 24 degrees at the end of August, I believe; But the temperature can reach 24 degrees at the end of February. I absolutely don't believe it. Not to mention the Central Plains, Hainan may not reach this standard at the end of February!
There is also warm and humid air flow in winter in China, but it enters China from the southwest Indian Ocean through the Hengduan Mountains. The warm and humid air flow of China's real summer monsoon comes from the southeast Pacific Ocean, which is brought by the southerly air flow on the west side of the subtropical high. When the warm and humid airflow comes, the cold air is heavier than the warm air, so the cold air at the bottom and the warm air at the top climb to form rainfall. Therefore, the warm air of summer monsoon comes for the first time, which brings not warmth, but rain. From this point of view, it is very correct to describe the end of winter with rain, which shows this climate feature.
From May to August in summer, the ridge line of the subtropical high slowly rises northward and collapses thousands of miles in September, so the process of the Central Plains entering autumn is quite fast. In contrast, the process of entering the spring for half a year is much slower. It can be considered that "a spring rain and a warmth" before the rainy season, but the cold in late spring occurs from time to time, and the temperature rises with twists and turns.
From this point of view, people's perception of temperature is asymmetric with the seasons; Rain can better express seasonal characteristics; The process of turning cold is completely different from that of warming, which is why "rain" is used instead of "keeping cold".