What is a subtropical high? I can't read the geography notes of senior one.

The subtropical high here refers to the subtropical high. The meteorological term of subtropical high (also known as subtropical high, subtropical high and subtropical ridge) refers to the warm and high pressure system located in subtropical areas. In the subtropical region of the northern and southern hemispheres, a discontinuous high pressure area along the latitude circle is often maintained, which is the subtropical high pressure area. Due to the influence of land and sea, it is often divided into several high-pressure units, which are collectively called subtropical high.

Subtropical high pressure plays an important role in the transport and balance of water vapor, heat and energy between middle and high latitudes.

classify

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. Subtropical high can also be divided into smaller high-pressure cells, and some small cells can also be located on the mainland. For example, the monomer located in the South China Sea in winter is called the South China Sea High.

Case analysis

In this paper, the Pacific high, the Qinghai-Tibet high and the Mexican high are taken as examples to analyze:

1, Pacific High School

Summer is 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, there are frequent cyclones and fronts, which often produce rainy or rainstorm weather. 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, in May, the ridge line of high pressure is located near north latitude 15, and the main rain belt is located in South China. In June, the ridge line crossed 20 north latitude, and the main rain belt was located in the middle and lower reaches of the Yangtze River and Huaihe River basin, which made the Jianghuai area enter the Meiyu period. In mid-July, the ridge line crossed 25 north latitude, and 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 Meiyu period ended and 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. 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 in the summer half-year weather forecast.

2. Qinghai-Tibet high and Mexico high

In warm season, there are two other large-scale warm and high-pressure systems in the upper troposphere of Asia and southern North America, which are called Qinghai-Tibet High (or South Asia High) and Mexican 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.

Influence of Subtropical High on China

The warm high which has an important influence on the weather and climate in China is the western Pacific subtropical high. The location of the western Pacific subtropical high changes with the seasons, generally moving between10 ~ 40 N.

In winter, the ridge line of subtropical high is located near15 N, and slowly moves northward with the seasonal warming. In April and May, the ridge line of subtropical high was at15-20 N, and the polar front rain belt landed in South China in April. From May to mid-June in Nanling, the subtropical ridge line jumped northward for the first time, crossing 20 N and hovering between 20-25 N; The polar front rain belt reached the Yangtze River basin, forming plum rain, when South China turned into sunny, hot and dry summer. In the middle and late July, the subtropical high ridge jumped northward for the second time. The ridge line quickly jumps over 25 N, then swings between 25 N and 30 N. The rainy season in the middle and lower reaches of the Yangtze River ends and the hot and dry weather begins. The Huanghuai area entered the rainy season under the influence of the polar front rain belt, while the tropical cyclones and typhoons in South China entered the second flood season, that is, the "late flood season", due to the convergence of the equator to the north. From the end of July to the beginning of August, the subtropical ridge jumped northward for the third time, crossed 30 N to reach the northernmost position and stayed there, and North China and Northeast China entered the rainy season. In late August, with the strong cold air moving southward, the subtropical high in the northwest Pacific weakened and the ridge line began to retreat rapidly from north to south. At the beginning of September, the ridge line retreated to about 25 N for the first time, and the weather in China changed from north to south to crisp in autumn. 10 year1early October, the subtropical ridge retreated to the south of 20 N, ending the seasonal north-south movement with a one-year cycle.

Subtropical high prevailing downdraft, sunny weather. When the subtropical high controls a certain area for a long time, it often causes drought in this area. The northern side of the western Pacific subtropical high is the mid-latitude westerly belt, which is also the location of the subtropical front. The southerly airflow on the west side of the subtropical high can bring rich water vapor from the sea surface and transport it to the lower layer of the front, forming a warm and humid conveyor belt in the edge area from the west side to the north side of the subtropical high, and continuously transporting high-temperature and high-humidity airflow to the front area on the north side of the subtropical high. When the west wind moves through the front area in a trough or vortex, rich water vapor condenses under the combined action of the ascending motion of the system caused by unstable energy release, resulting in a wide range of precipitation and rain belts, usually accompanied by heavy rain. According to statistics, the position of rain belt is generally 6 ~ 10 latitude north of the ridge line of subtropical high, and its trend is roughly parallel to the ridge line.

The position of subtropical high is closely related to the position of rain belt, so the abnormal change of subtropical high will often cause drought and flood disasters in various regions, such as 1954, 1980, 199 1 year, where the ridge of subtropical high hovers for 20 ~ 25 N for a long time, and the rain belt is stable in the Jianghuai basin, resulting in Jianghuai. However, in 1978 and 1983, the ridge line of subtropical high quickly crossed 20 ~ 25 N, reaching about 30 N, and the rain belt basically did not stabilize in the Jianghuai basin for a period of time, and the Jianghuai area was under the control of subtropical high for a long time, resulting in drought in this area.