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20 14 The Second Mode of Shanghai History
(1) Shanghai is located in the meiyu distribution area, so the weather system in Shanghai is a quasi-static front. The characteristics of quasi-static front are that the cold and warm air currents on both sides of the front are evenly matched, and the front stays for a long time, resulting in continuous rainy weather.

(2) The Meiyu belt in the figure is located on the north side of the edge of subtropical high. When the subtropical high is strong, Wuhan area is controlled by the subtropical high, and the rainy season is shortened or "empty", with less precipitation. When the subtropical high is weak, Wuhan is located on the north side of the subtropical high, with a long rainy period and a lot of precipitation.

(3) The main frontal rain belt in eastern China is usually located at 5-8 latitudes north of the ridge line of the western Pacific subtropical high, and moves with the northward advance and southward retreat of the western Pacific subtropical high. The reasons for the slow advance to the north are as follows: in early summer, the warm air from the low-latitude ocean heats up slowly, and the summer monsoon is weak; The cold air force in the mainland is still strong, and the subtropical high (ridge) blocks it, so it is slow to go north and fast to go south. Reason: In early autumn, the cold air from high latitude Eurasia (Asian high pressure) cools down quickly and the wind is strong in winter; The warm air power of the mainland is already very weak; The terrain with high northwest and low southeast further strengthens the influence of winter wind southward, forcing the rain belt to withdraw southward quickly.

So the answer is:

(1) quasi-static stop loss?

? The cold and warm air currents (temperature and air pressure) on both sides of the front line (surface) are evenly matched, and the front line stays for a long time, resulting in continuous rainy weather.

(2) Meiyu belt is located at the northern edge of subtropical high.

When the subtropical high is strong, Wuhan area is controlled by the subtropical high, so the rainy season is shortened or "empty" and the precipitation is less; When the subtropical high is weak, Wuhan is located on the north side of the subtropical high, with a long rainy period and a lot of precipitation.

(3) Reasons for slow northward movement: the warm air from the low-latitude ocean warms up slowly in early summer, and the summer monsoon is weak; The cold air force on the mainland is still strong, blocked by subtropical high (ridge) and moving slowly northward.

The reasons for the rapid withdrawal from the south are as follows: in early autumn, the cold air from high latitude Eurasia (Asian high) cools faster and the winter wind is stronger; The warm air power of the mainland is already very weak; The terrain with high northwest and low southeast further strengthens the influence of winter wind southward, forcing the rain belt to withdraw southward quickly.