Why is there a "return to the south sky" in winter?

southerly days are also called returning to the south. Generally speaking, it happens in the spring in the south and occasionally in the north. It usually happens in April of Gregorian calendar or after the rainy season. The north calls this kind of weather a return tide, which usually lasts for a short time.

There are four distinct seasons in the north, and the indoor air is often heated in the cold season, so the indoor humidity is much higher than that of the outdoor air. Therefore, in spring, after the outdoor temperature rises, the indoor temperature is still higher than that of the outdoor air, so it is difficult to have a southerly day, because the water vapor condenses more easily in the outdoor air with lower temperature.

In the south, it is different. After going south because of strong cold air or the rainy winter season, the indoor temperature often drops to a lower level.

The main damage of southerly days is that the rapidly increasing steam changes phase when it meets a cold object, and quickly condenses and adheres to the cold object. The greater the temperature difference, the faster the adhesion speed.

Therefore, once there is too much water vapor in the air, a large number of water droplets will easily condense on cold objects. Water droplets breed algae and mold, causing a large area of mildew; Water droplets lead to the decrease of insulation value, resulting in short circuit or poor contact;