Why is it getting colder and colder in Kunming?

Because of the quasi-static front station activity in Kunming

Quasi-static Front in Kunming and Yunnan-Guizhou Weather

Kunming quasi-static front, also known as Yunnan-Guizhou quasi-static front, was formed under the influence of special terrain and certain weather system in the northeast of Yunnan-Guizhou Plateau. It is a climate front with constant position, which has great influence on the weather and climate in Yunnan-Guizhou area.

I. Characteristics of the activity

Except in July, the areas with the highest frequency of quasi-static front activity in Kunming are located in southwest Sichuan, northeast Yunnan and southwest Guizhou.

The quasi-static frontal activity in Kunming has obvious seasonal characteristics. It mainly appears in June 1 1 to April of the following year, and often lasts for 10 ~ 15 days. Among them, 12 ~ 2 months, about half of the days appear; In April, May, 10, 1 1 appear less frequently, ranging from 10- 12 days per month. From July to August in summer, the influence of cold air is greatly weakened, and the activity position is also northward. Yunnan-Guizhou area is controlled by equatorial air mass and tropical air mass, so it rarely appears, only about 3 days. In the whole year, the activity frequency is the highest in June 5438+ 10, followed by April, with less in June 5438+ 10, and basically does not exist in July.

The quasi-static front in Kunming is not "static", it often swings around a certain position, and it also retreats to the north during the day and advances to the south at night, which is more obvious when the static front is weak.

Second, the formation mechanism

The causes of quasi-static fronts in Kunming can be divided into two categories:

1, and the cold front weakens into a quasi-static front.

Most of the cold air that hits the southwest in winter comes from the Arctic Ocean, Barents Sea and Lake Kara, and a small part comes from the ocean surface south of Iceland. This deep cold air generally accumulates in northern Siberia and Mongolia first, which strengthens the cold high pressure on the mainland. When the strong fluctuation of westerly belt pushes eastward, it will often break the low-level continental high, leading to the outbreak of cold air to the south. The main path of cold air affecting southwest China is from Siberia to Xinjiang; Blocked by the large terrain of the Qinghai-Tibet Plateau, it flows around the plateau, crosses the Hexi Corridor, crosses the Qinling Mountains, enters the south of the Sichuan Basin, and then climbs the Yunnan Plateau and the northeast of the Guizhou Plateau along the east side of Daliangshan Mountain. Due to the blocking of a series of mountains on the Yunnan-Guizhou Plateau, the cold air gradually quieted down, that is, it changed from a cold front to a quasi-static front, which is the famous quasi-static front in Kunming. (Figure 1)

What must be explained is the source and nature of warm air on the front. After entering the winter half year, the planetary wind belt moves south, the subtropical high center moves south to the north latitude15 ~ 20, and the westerly wind belt also moves south. Blocked by the Qinghai-Tibet Plateau, the west wind is divided into north and south. The westerly airflow of the northern branch flows to the Pacific Ocean through the northwest, north China, northeast China and east China. The southerly westerly airflow flows eastward along the southern edge of the plateau, that is, from the tropical deserts and inland areas of Arabian Peninsula, Iran, Pakistan and northern Indian Peninsula to Yunnan. Because Jinniu Mountain, Caucasus Mountain and Iranian Plateau form a strong barrier to the cold air from Europe and Central Asia from west to east, the airflow in the south branch is very dry and warm. Although there is a certain uplift along the front, it can not form obvious cloud system and precipitation. In the process of cold air heading south, a lot of water vapor was added along the way. After entering the Yunnan-Guizhou Plateau, it gradually cools and turbulently mixes along the slope, showing a cloud system structure dominated by middle and low clouds.

About 85% of the quasi-static front in Kunming lies between Kunming and Guiyang (Figure 2). On the ground map, Mongolia is a strong cold high pressure, southwest Yunnan is a hot low pressure, and the ground front line is slightly northwest-southeast. If the cold air is strong, the front can be located in the south of Kunming; When the cold air activity range is large, the southeast can be connected with the quasi-static front in South China (Figure 3). If the cold air is weak, the quasi-static front may also be located in the north of Guiyang.

2. The southwest vortex moves eastward to form a quasi-static front.

This quasi-static front is formed by the eastward movement of southwest vortex and the strengthening of cold advection after vortex. Compared with the former, the scope is smaller, the maintenance time is shorter and the strength changes faster.

It can be clearly seen from the satellite cloud picture that it is roughly consistent with the topographic contour line, and the cloud belt is located at the back of the front.

Third, the impact on the weather and climate in Southwest China

As mentioned above, the quasi-static front in Kunming is the interface between the polar metamorphic continental air mass and the tropical continental air mass. The front slope is very small, generally below 1/250, covering a wide area. Meteorological factors such as temperature, sunshine, wind and relative humidity on both sides of the front are obviously discontinuous, and the weather characteristics are quite different. Most parts of Yunnan, located on the southwest side of the front, are controlled by a single warm air flow, with blue sky, bright sunshine and high temperature. For example, the average temperature in Kunming in June 5438+10 was 7.7℃, and there was no severe cold in winter. Most of Liangshan Prefecture, Sichuan, Northeast Yunnan and Guizhou under the front are located on the cold air side, with northerly winds and low temperatures. For example, in June 5438+10/October, the average temperature in Guiyang was 5.0℃, and it rained continuously; The number of days of precipitation ≥ 0. 1mm per month is more than/kloc-0 ~15 days, so it is said that there are no three sunny days.

When the cold air is strong and the front is located to the west of Kunming, the eastern part of Yunnan is below the static front, the temperature drops suddenly, and the weather turns cloudy or there is light rain. Therefore, there is also a saying in Yunnan that "there is no cold and heat in four seasons, and it becomes winter when it rains".

This front is the northern boundary of the dry and warm continental air mass that controls Yunnan, and it is also the northern boundary of the monsoon climate in Yunnan. During this period, northeastern Yunnan and most parts of Guizhou were controlled by cold air moving at mid-latitude. Now take Kunming and Guiyang as representatives to illustrate their differences.

First of all, the four seasons in Kunming are not clear. According to the standard of dividing the four seasons proposed by Mr. Zhang Baokun (that is, the average climate temperature < 10℃ is winter, 10 ~ 22℃ is spring and autumn, and > 22℃ is summer), it can be seen from Figure 4 that there is no summer in Kunming all the year round, and spring and autumn are connected for about 9 months. Guiyang has four distinct seasons.

Secondly, Kunming has the characteristics of small temperature annual range and large daily range; In Guiyang, however, the annual range is larger, and the daily range is smaller (table 1).

Third, the dry and wet seasons in Kunming are more distinct than those in Guiyang. As can be seen from Table 2, the dry season in Kunming is from June to April, and the precipitation only accounts for 1 1.2% of the whole year. The precipitation ≥0. 1mm is only 3 1 day, 50 days less than Guiyang, and the relative humidity is 66% less than rainy season.

2006 South China Industrial Engineering Annual Meeting (4th) 40% Detailed Rules for the Development of Science and Technology in Yangzhou during the 11th Five-Year Plan of Chengdu University of Traditional Chinese Medicine The quasi-static front stop in Kunming and the quasi-static front stop in Yunnan-Guizhou weather, also known as the quasi-static front stop in Yunnan-Guizhou Plateau, were formed under the influence of special terrain and certain weather system in the northeast of Yunnan-Guizhou Plateau. It is a climate front with constant position, which has great influence on the weather and climate in Yunnan-Guizhou area. I. Activity characteristics Except in July, the areas with the highest frequency of quasi-static front activity in Kunming are located in southwest Sichuan, northeast Yunnan and southwest Guizhou. The quasi-static frontal activity in Kunming has obvious seasonal characteristics. It mainly appears in June 1 1 to April of the following year, and often lasts for 10 ~ 15 days. Among them, 12 ~ 2 months, about half of the days appear; In April, May, 10, 1 1 appear less frequently, ranging from 10- 12 days per month. From July to August in summer, the influence of cold air is greatly weakened, and the activity position is also northward. Yunnan-Guizhou area is affected by quasi-static front of equatorial Kunming and Yunnan-Guizhou weather.