How did sauna days come into being?

Generally speaking, hot and humid weather appears in the area controlled by the subtropical high in the northwest Pacific and the ridge or edge area of the subtropical high, which is easy to produce sauna days. In these areas, the downward flow makes the temperature rise, the temperature is high, the ground water vapor evaporates quickly, and the air humidity is high; At the edge of subtropical high, there is always warm and humid air input, and the air humidity is also high. The general temperature of sauna days is above 32℃, and the lowest relative humidity reaches 80%. "Sauna day" generally refers to the weather where the temperature is above 32℃ and the lowest relative humidity reaches 80%. The reason for sauna days is that rainfall increases the relative humidity of the air and the ground temperature is low, while the upper air temperature is relatively high, the wind is small and the air circulation speed is slow. Taking the sky refers to the weather phenomenon of high temperature and high air humidity. High air humidity (often accompanied by still wind) will make human sweat unable to be discharged, and at the same time lead to the inability to dissipate heat in the body, which makes people feel particularly uncomfortable. Comparatively speaking, dry and hot weather can make sweat evaporate quickly, but people won't feel too uncomfortable. In meteorology, there is no standard and clear definition of the so-called "sauna day". According to the data of previous years, when the highest temperature exceeds 32℃ and the average daily humidity exceeds 65%, it can be called sauna days.

The "sauna days" in the south are often due to the rainy season in the south of China. It's hot and humid at this time, and it often happens when it doesn't rain. Jiang Nanyu belt moves with the position of subtropical ridge. And mobile, because "sauna days" have a greater impact on the middle and lower reaches of the Yangtze River (first, the Yangtze River Delta has a large population and a great impact. The subtropical high that affects China is located in the western Pacific Ocean, which is referred to as the western Pacific subtropical high for short, and sometimes directly called the subtropical high, which will not cause misunderstanding. As the protagonist of summer weather life in central and eastern China, subtropical high directly controls the rain belt and sunny and hot weather.