In midsummer, there is a folk saying that July and August are-

Qiao Yun refers to strange and changeable clouds.

Qiao Yun in July refers to the overlapping convective clouds formed in July due to the evaporation of water vapor on the ground caused by high temperature and scorching sun. Clouds in the sky change into various shapes. Seeing the strange and changeable white clouds in the sky in July is a holiday custom and one of the pleasures of the festival.

Clouds are a symbol of sunny days and a harbinger of rainy days. In ancient times, people learned about the weather by looking at the clouds, accumulated a lot of experience, and left many related proverbs, such as "cotton clouds, rain showers are fast", "gray cloth hangs in the sky, rain will continue", "don't go out at sunrise, travel thousands of miles at sunset" and so on.

In the long-term careful observation of natural images, people find that the sky in July is clearer and bluer, wider and higher, and the clouds are changing and charming. As a result, there is a folk custom of "seeing a clever cloud in July and August".

First, why is the cloud changeable?

This mainly depends on the air flow. For example, when the airflow is stable and the water vapor rises slowly, a flat and wide layered cloud will be formed; When the airflow is strong, the moisture rises rapidly.

It will form vertical cumulonimbus clouds, just like a natural aerodynamic laboratory. Every change in airflow may create a new cloud shape.

We can see clouds of various shapes because our brains have an innate ability to discover and interpret shapes, which is what we call "pattern recognition".

Sometimes we can see animals, faces and even all kinds of strange images in the clouds, which are all our brains interpreting visual information.

Second, the meteorological changes of summer solar terms

After the summer solstice solar terms, although the subtropical high strode south, it would never give up its dominant position easily and easily retreat into the sea of the western Pacific. In the southern region under its control, it is often late summer, and it feels hot weather. This is the short-term regenerative weather "autumn tiger".

The duration of autumn tigers varies from year to year, usually lasting from half a month to two months. The reason for the formation of the autumn tiger is that the western Pacific subtropical high that controls China in autumn gradually moves southward, but then moves northward. Controlled by subtropical high, it is cloudy locally, cloudy between sunny days, strong sunshine and rising temperature.