Why are there empty plums?

In normal years, from mid-June to early July, the subtropical high zone is stable at 20 ~ 25 north latitude in Chinese mainland, bringing continuous precipitation to the northern Jianghuai area, which is called "Meiyu". However, in some years, due to the overall changes of global atmospheric circulation (such as El Ni? o phenomenon and La Ni? a phenomenon), the position change of subtropical high will be affected (because the global climate is interactive, one change cannot be seen in isolation). Therefore, in some years, the subtropical high will jump northward (move northward) too quickly. At this time, the Jianghuai area will be controlled (it should be July and August), and the downward flow will prevail, so naturally it will not rain. There is no rain in the rainy season, so it is called "empty plum". At this time, North China will be miserable. Entering the rainy season ahead of time will often lead to floods, and the Jianghuai area will be affected by drought.

Further expansion, in some years, the subtropical high becomes very stable, and the rainy season stays at 20 ~ 25 north latitude for a long time. In this case, the rainfall time in the Jianghuai area will become particularly long, which will often lead to floods in the Yangtze River, but the South China area controlled by the high pressure area will be particularly dry.

PS: Rain belts are all formed in the northern part of the subtropical high. Because the airflow sinking to the north meets the cold air mass in the north to form a front, and because the humid summer monsoon blowing from the Pacific Ocean prevails in eastern China in summer, rainfall is formed.

Let's answer so many questions first I have a paper to catch up on. I don't know if you are a high school student or a teacher, so let's answer so much first. I believe you can understand everything. Talk to you later, 88~