Why is there summer drought in the middle and lower reaches of the Yangtze River in China?

The reason for the "summer dry weather" in the middle and lower reaches of the Yangtze River is that around April every year, warm and humid air from the Pacific Ocean begins to land in China and meet the Mongolian high pressure entrenched in Chinese mainland. The interface between cold and warm air is called front. When cold and warm air meet, it will rise because of the low density of warm air. With the increase of height, the ability of air to contain water vapor will decrease, so it is easy to form precipitation, which is called frontal rain. In early April, the rain belt was in South China. In June, it is called Meiyu in Jianghuai area. Since then, with the direct point of the sun moving northward, the temperature in the northern hemisphere has been rising, the power of warm air has become stronger and stronger, and the cold air has been retreating northward, so the front has not moved northward. At this time, the warm and humid air flow controls the south of China, including the middle and lower reaches of the Yangtze River. The weather under the control of warm and humid airflow will not produce drought. Therefore, it cannot be said that the northward movement of the front caused the summer drought in the middle and lower reaches of the Yangtze River. The lower reaches of the Yangtze River are also hot and rainy in July and August in normal years. However, if the western Pacific subtropical high is stronger than in previous years, it will extend westward to the mainland and control the middle and lower reaches of the Yangtze River in China. Under the control of subtropical high, downflow prevails, and the weather is dry and rainy. At the same time, because of its powerful force, it will push the front northward ahead of time, making the south extremely dry, which is the summer drought in the lower reaches of the Yangtze River. At this time, the rain belt moved northward in advance, which made the rain belt stagnate for a long time. there is a