What studies did China have on clouds in ancient times?

China has attached great importance to the change of cloud since ancient times. It is mentioned in "Pipe Scrap" that the change of weather can be inferred from the change of the shape or color of clouds, and the book writes: "If the clouds are relatively flat, there will be no heavy rain. When it rains, if there is no cloud water supply, the rain will not last long and will end soon. " Only by observing the cloud very carefully and raising it to a certain level of rational understanding can ancient people come to such a conclusion. In Lu's Poems of Wandering in the Spring and Autumn Period, clouds are divided into four types according to their shapes: mountain clouds, water clouds, dry clouds and rain clouds.

In China, there have been many weather proverbs about clouds for a long time. For example, in the book A Supplement to National History in the Tang Dynasty, it was recorded that "there are cannon clouds when there is wind and rain". Another book in the Tang Dynasty, Xiang, also said: "If the cloud is like a fish scale, the wind will be the strongest the next day." There is such a weather proverb in the book "Yuan Tan" in the Song Dynasty: "Clouds go south, rain pools; Yun Qi faces north, and the old crane cries for the river; The clouds are heading west, and the rain is not cultivated; The clouds are going east, and the dust is not old. " This sentence connects clouds with sunny rain, which is very scientific.