Articles and pictures about weather changes

subtropical high

Located in the subtropical zone (latitude about 20? ~30? ) of the high pressure system. It is oval, and its long axis is roughly parallel to the latitude circle. It is a warm dynamic system, which is most obvious on the isobars of 700 hectopascals and 500 hectopascals, and belongs to a planetary scale system. Subtropical high plays an important role in the transport and balance of water vapor, heat, energy and angular momentum between middle and high latitudes, and is an important system of atmospheric circulation. Subtropical high is mainly located in the ocean and exists all the year round. According to different geographical locations, they are called North Pacific High, North Atlantic High, South Pacific High, South Atlantic High and South Indian Ocean High respectively. Because these high-pressure packages surround the whole subtropical region, they are collectively called subtropical high-pressure areas. Sometimes, the subtropical high can be divided into smaller high-pressure units, and some small units can also be located on the mainland. The monomer located in the South China Sea in winter is called the South China Sea High.

The main cause of the characteristic subtropical high pressure belt is the action of power, and its high pressure ridge line (the line connecting the isobar or contour line with the maximum anticyclone curvature) is located in the downflow area of Hadley meridional circulation and Ferrer meridional circulation, and the weather is clear. According to legend, when the horse-carrying sailboat from the Atlantic Ocean to the West Indies entered the latitude where the subtropical high was located, it was calm for several weeks, and finally it had to be thrown into the sea because of the exhaustion of water and food. Therefore, horse latitude is often regarded as synonymous with subtropical high in Europe and America. As far as the subtropical high is concerned, the vertical motion of the atmosphere between the east and the west is quite different: in the east of the high, the sinking motion is particularly strong, and the descending airflow is heated by adiabatic compression, resulting in a strong subsidence inversion, which is called trade wind inversion. This strong inversion stratification is very stable, which inhibits the development of vertical movement of the atmosphere, makes the weather continue to be fine, and forms a dry climate zone on the west coast of the subtropical continent. In the west of high pressure, the downdraft and inversion layer are weak, which makes the warm and humid air converging and rising in the lower layer easily break through the inversion layer to form convection, so there are many thunderstorms.

With the change of seasons, the direct solar area moves north and south, and the intensity and position of subtropical high pressure area and high pressure unit also change obviously with seasons. Whether in the southern hemisphere or the northern hemisphere, 1 By July, the main body of high pressure moved northward and westward, and its intensity increased. From July to 65438+1October, it moved to the south-east direction, and its intensity also weakened. This seasonal change also has obvious slow and jumping stages.

In summer, the western Pacific high and the north Pacific high are generally divided into two large units: the large unit located in the western Pacific is called the western Pacific high and the large unit located in the eastern Pacific is called the eastern Pacific high. In the westerly belt on the north side of the ridge line of high pressure in the western Pacific, the front is active frequently, and rainy or rainstorm weather often occurs. The main rain belt in eastern China is often located at a distance of 5 ~ 8 latitudes north of the ridge line of high pressure. The seasonal variation of the ridge line of high pressure in the western Pacific corresponds to the seasonal displacement of the main rain belt in eastern China. On average, the ridge line of high pressure in May is located at 15? Nearby, the main rain belt is located in South China. In June, the ridgeline crossed the latitude of 20? The main rain belt is located in the middle and lower reaches of the Yangtze River and Huaihe River basin, which makes the Jianghuai area enter a period. In mid-July, the ridgeline crossed the latitude of 25? The main rain belt moved to the Yellow River basin, making North China enter the rainy season. At this time, the Jianghuai Basin was controlled by the ridge line of high pressure, and the rainy season ended and it entered the summer drought period, with hot weather and little rain. On the south side of the ridge line is the easterly belt, where there are often easterly waves and typhoons, which produce a lot of precipitation. So after mid-July, another rain belt appeared in South China. The mutual configuration of the western Pacific high and typhoon determines the moving path of typhoon. When the high pressure is strong and the ridge line is east-west, the typhoon is stable to the west; When the ridge line of high pressure is northwest-southeast, the typhoon is easy to move to the northwest and land in China. If the high pressure weakens and breaks, typhoons usually land or turn north. [Gradual change of subtropical high ridge position on 500 HPA isobaric surface in northern hemisphere]

The intensity, advance, retreat and movement of the western Pacific high are closely related to the weather, drought and flood in eastern China, and it is one of the weather systems that need to be analyzed and studied emphatically in summer half a year.

Qinghai-Tibet High and Mexico High In the warm season, there are two other large-scale warm high-pressure systems in the upper troposphere of Asia and southern North America, which are called Qinghai-Tibet High (or South Asia High) and Mexico High respectively. The horizontal scale of Qinghai-Tibet high can reach more than 10,000 kilometers, belonging to the ultra-long wave system. Although both of them are located in the subtropical zone, they are very different from the subtropical high in the middle and lower troposphere in terms of structure, nature and formation process. They are mainly formed by plateau or continental heating. This system is characterized by thermal low pressure below 500 hectopascals and high pressure above 500 hectopascals, and the higher the pressure, the greater the strength, and the highest strength is at the height of 200 ~ 100 hectopascals. Its high pressure center area is updraft, and there are many convective activities. These high-pressure centers often swing from east to west, and when they swing eastward, they overlap with the subtropical ridge of the western ocean, strengthening the latter. The intensity of ocean subtropical high in the northern hemisphere is stronger in summer than in winter, which is closely related to the existence and function of these high pressures.