What is the vacuum zone in rainy areas in the middle and lower reaches of the Yangtze River in July and August? And how did the rain belt from the ocean form in March and April? geography

1 Controlled by the Pacific subtropical high, the middle and lower reaches of the Yangtze River have strong solar radiation, high temperature, low humidity and large evapotranspiration.

In March and April every year, the warm and humid air current (that is, the rain belt) on the surface of the Southern Ocean begins to move northward, and there is continuous rainy weather from south to north in China. The rain belt moves to the middle and lower reaches of the Yangtze River, usually in May and June, that is, the rainy season, commonly known as "yellow mold" days, and then the rain belt continues to move northward. To the north of Huaihe River, usually in July and August. At the same time, under the control of subtropical high, there will be hot and sunny weather in the middle and lower reaches of the Yangtze River for nearly two months, which is the cause of "summer drought" you want to know. Due to the periodicity of the earth's revolution, there will be dry days in July and August every year. After August, the dry weather in the middle and lower reaches of the Yangtze River will come to an end because of the rain belt returning to the south.

Under the condition of uniform ground, the subtropical high belt is distributed in a strip shape around 30 degrees north and south latitude, but due to the north-south movement of the direct point of the sun, the subtropical high also moves north and south, moving north in summer and south in winter. Under the control of subtropical high, the airflow sinks and the weather is hot and dry.

Because the surface is uneven, especially in the northern hemisphere, there are many continents and few oceans, and the zonal subtropical high is destroyed, leaving only the oceans. When the North Pacific subtropical high moves northward in summer, its western end just controls the middle and lower reaches of the Yangtze River. So it is hot and dry, and no precipitation can be formed. Because this phenomenon appears in the dog days, people call it summer drought.