Using geographical knowledge to explain the causes of "Shu dogs barking at the sun", "late rain" and "Ya 'an leaking the sky"

Sichuan basin is a closed basin. The mountains in the north are relatively high, and the mountains and plateaus in the south are relatively low, which is beneficial to the southeast and southwest airflow to bring in water vapor, but the water vapor brought in is not easy to be brought out from the north, which leads to the high humidity state in Sichuan Basin all the year round (including winter), and the relative humidity reaches or approaches the critical saturation state for many days.

In this kind of high humidity weather, when night falls, the temperature drops, the air humidity will exceed the saturation limit, and the water vapor will condense into rain fog, so many nights in Sichuan Basin are rainy and foggy.

There is a popular misconception that the temperature drop in Sichuan Basin is relatively fast at night, and the temperature difference between day and night is relatively large, so water vapor is easy to condense into rain. This is not correct. The fact is that the temperature drop in Sichuan Basin is not fast at night. On the contrary, the temperature drop in Sichuan Basin is very slow, which is one of the regions with the smallest temperature difference between day and night in China, smaller than that in most coastal maritime climate regions.

Rainy nights in Sichuan Basin are due to high relative humidity, which is usually close to saturation during the day. When the temperature drops slightly at night, it will condense into rain. At the same time, due to the condensation of water vapor, the temperature difference between day and night is very small, which will release a lot of heat.

2, shu dog barking at the sun:

Sichuan Basin has humid air and cloudy sky. Surrounded by mountains, the water vapor in the central plain is not easy to disperse. Dogs there don't often see the sun. They feel strange when they see the sun, so they bark. Therefore, there is a saying in Shu that "it will be sunny for three days" and "Shu dogs bark at the sun". This idiom usually means that it is rare and strange.

3. Ya 'an Tianlou:

To the west of Ya 'an is the Qinghai-Tibet Plateau known as the roof of the world, and to the east is the Sichuan Basin thousands of miles away. Ya 'an is located between these two completely different landforms, and is often influenced by the warm and humid airflow flowing downward from the plateau and basin. In addition, the westerly winds from the South Indian Ocean are often forced to move eastward around the plateau into Ya 'an. These air currents interact, leading to more rainy days, longer rainfall and more heavy rain.