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Dense fog, long-term low temperature and damp heat appear.

In spring, water will come out from the walls and floors in the southern sky, which is actually very similar to the principle of sea fog. Warm and humid ocean air flows from the warmer sea surface to the colder sea surface, and the water vapor in the air condenses into water droplets and accumulates in the air to form fog. If the temperature difference between the sea surface through which the airflow passes is large, there is a greater chance of forming fog. Similarly, due to the cold weather in winter, the walls and floors are very cold inside and outside. If warm and humid air flows through the walls and floors at this time, the water in the air will condense into water droplets and adhere to the walls and floors, just as water seeps from the walls and floors. In summer, even if there is humid ocean airflow, the walls and floors are not cold enough inside and outside, and the walls and floors will not get out of water.

The tropic of cancer in the south is more serious, which is related to the sea and humid air in the south. When Return to the South Sky appeared, the air humidity was close to saturation, and the walls and even the ground would "bubble". Everywhere is wet, and the air seems to be able to wring water out. Dense fog is the most distinctive appearance of "returning to the south sky"