In the subtropical regions of the northern and southern hemispheresSubtropical high belt。The subtropical high is mainly located on the ocean and exists all the year round. It is calledNorth Pacific High, South Pacific High, North Atlantic High, South Atlantic High and South Indian Ocean High.The high pressure in the Pacific Ocean is also called the Pacific High.
The subtropical high is one of the important members that restrict the change of atmospheric circulation.stayGround mapThe Pacific region is often controlled by a high pressure, called the Pacific subtropical high.The Pacific high exists all year round, and it is a warm and deep system with stability and little movement.In summer, the Pacific High is very strong and has a wide range;In winter, the intensity is weakened and the scope is narrowed, mostly in the shape of east-west flat and long, with two centers located in the eastern and western Pacific Ocean respectively.The Western Pacific High is one of the persistent large-scale weather systems that control the tropics and subtropics, and directly controls and affects thetyphoonThe western ridge in summer can extend to the mainland of China, which has an important impact on the weather characteristics of China.
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Temperature field and humidity field
The Pacific subtropical ridge mainly refers to the situation of 500 hPa and below. Its strength increases with height because of the significant temperature difference between land and sea.The heat source on the ocean is located on the south side of the Pacific high, and the heat source on the continent is located on the north side of the high.In summer, the temperature on the mainland and coastal areas is relatively high, and the high pressure above it increases rapidly with height, while the high pressure over the ocean is not.There is usually a temperature inversion layer in the lower layer of the Pacific ridge. The humidity in the lower part of the temperature inversion layer is high, while that in the upper part is low.The high pressure ridge is generally dry, with the driest area overlapping with the ridge line, and the south and north edges of the high pressure have wet areas.
Wind field
The horizontal wind speed near the ridge line of the Pacific subtropical high is small, and the horizontal wind speed on the north and south sides is large, and also increases with the height. When reaching a certain height, a westerly jet stream forms on the north side, and an easterly jet stream forms on the south side.When the ridge of subtropical high moves southward and northward, the position, height and intensity of easterly and westerly jet streams change accordingly.
Vorticity field and divergence field
Within the Pacific subtropical high, the vorticity field is evenly distributed, while the divergence field is more complex.At the lower level of the high pressure area, the southern part is mainly divergent, and the northern part is mostly convergent;The northern part of the upper level is divergence, and the southern part is convergence and diffusion to the high pressure center. The intensity of convergence and divergence is large.
vertical velocity
In the middle and upper troposphere, the southern side of the high pressure ridge is dominated by subsidence, while the northern side and the ridge line are dominated by upward movement;Subsidence movement near the ridge line in the lower troposphere[1]。
The relationship between the western pacific high and the weather in china
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Relation with rainy season
The activity of the Pacific ridge is closely related to the precipitation in China.The warm air mass generated and sent out by the Pacific High meets the cold air mass of the mid high latitude continent, forming a front and causing a lot of precipitation.With the south-north advance and retreat of the ridge line of the Pacific High, the rain belt in eastern China also moves with it.
Before June, the western ridge line of the subtropical high in the middle and lower troposphere was mainly active south of 20 ° N, and the rain belt hovered in the area south of the Yangtze River;In the middle of June, the ridge line often jumps to the north near 25 ° N, forming a quasi quiet front in the high altitude, and the ground rain belt hovers in the Yangtze Huaihe River basin, forming a plum rain weather;In the middle of July, the ridge line jumped northward for the second time, maintained around 30 ° N, and the rain belt moved northward to North China;After September, the ridge line moved southward, and the rain belt moved southward;After mid October, the ridge line returned to the position before June.
In summer, all provinces (cities and autonomous regions) in southern China can be directly controlled by the western ridge line of the Pacific High, which is located in its southwest, so the wind is generally southeasterly.Although the southeast wind brings warm and humid air at sea, the air layer is relatively stable under the action of downdraft, and there is no cloud or rain during the day, so the weather is extremely hot.If it lasts for a long time, it often causes summer drought in the middle and lower reaches of the Yangtze River.
Relation with typhoon moving path
Typhoons that affect China are mostly formed over the Pacific Ocean, the southern edge of the Western Pacific subtropical high, and then move along the edge of the high pressure. Therefore, the movement and deformation of the high pressure will have an impact on the path of typhoon movement. The main forms of impact are as shown in Figure 1.When the subtropical high forms an east-west belt with strong intensity, the typhoon will travel westward along the edge of the subtropical high (Figure 1a);When the ridge retreats eastward, the typhoon turns northward (Fig. 1b);After the typhoon crosses the high pressure ridge line, the high pressure ridge extends westward, and the typhoon moves eastward along the edge of the high pressure (Figure 1c).If the subtropical high is weak, the typhoon located at the south side of the subtropical high can directly cross the ridge of high pressure, cut it off and move north directly (Figure 1d).
Figure 1 Relationship between Pacific subtropical high and typhoon track
