Genesis and characteristics of quasi-static front in Kunming

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)

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.