Why is the rainy season in some years in Shanghai obviously longer than normal, and there are few rainy days in some years?

In terms of air pressure, because Shanghai is controlled by subtropical high, in some years, the subtropical high (whose center is the Hawaiian islands in the Pacific Ocean, the scientific name is Hawaiian high) or the subtropical high is too strong, which leads to the decrease of rainy days in Shanghai and other places due to the prevalence of downdraft. On the contrary, the time will be too long.

As far as atmospheric circulation is concerned, because the Yangtze River basin (including Shanghai and other places) is between low-latitude circulation and mid-latitude circulation, cold air from the north and warm air from the south meet and meet here. If it is evenly matched, a quasi-static front will be formed, with rain on one side and sunny on the other. In the final analysis, the rainy days in Meiyu are related to the position and moving speed of the quasi-static front.

The climate and weather of a place should be analyzed from the aspects of solar radiation (atmospheric circulation), latitude, land and sea position, altitude and underlying surface. In short, physical geography is the most difficult and the best to learn! I wish you new progress and breakthrough in geography.