How is the heavy rainfall in North China and other places formed?
Expert: subtropical high pressure system, warm and humid airflow * * * with "director"
On 20th, the No.3 typhoon "Tian Ge" was generated in the northwest Pacific. During the day on the 23rd, it will land in the coastal area from Shenzhen to Maoming, Guangdong, with a peak landing. When the typhoon ravaged the south, there was a strong rainfall process in the eastern part of northwest China and north China from 2/kloc-0 to 23/north China. What is the scope and intensity of rainfall, and what causes it? In this regard, the Science and Technology Daily reporter interviewed Ma Xuekuan, chief forecaster of the Central Meteorological Observatory.
On August 22nd, it was influenced by the periphery of Typhoon Tian Ge. On the same day, Fujian Meteorological Observatory continued to issue a yellow warning signal for typhoon. China News Service reporter Zhang Bin photo
When it comes to the causes of rainfall, Ma Xuekuan's analysis is mainly the western extension of the subtropical high in the western Pacific, the interaction between warm and humid airflow around the subtropical high and cold air at mid-latitude. There are two warm and humid air currents at the bottom of troposphere, one is the southwest ring humid air current formed at the periphery of subtropical high, and the other is the southeast air current at the lower level, which transports water vapor to the northwest and north China. At the same time, there are high-altitude short-wave troughs in the Qinghai-Tibet Plateau and the mid-latitude westerly belt, which lead to the development of low-altitude systems such as vortex, shear line and southwest jet, leading to the strengthening of convergence and uplift.
"With abundant water vapor and strong convergence and uplift, there will be relatively strong precipitation, in which convective weather is dominated by short-term heavy precipitation, accompanied by thunderstorms and strong winds in the local area. The main rainfall areas appear in northern Shaanxi, northern Hebei, Beijing and Tianjin, and Heilongjiang, Jilin. The rainfall is generally between 30 and 80 mm, and the local processes in northern Shaanxi and central Shanxi will reach about 100- 130 mm, "Ma Xuekuan said.
As far as Beijing is concerned, Ma Xuekuan said that the main rainfall occurred from the night of the 22nd to the morning of the 23rd, and the accumulated rainfall in most areas was moderate to heavy rain and local heavy rain. The strongest precipitation period appeared on the night of the 22nd.
"It's always raining recently. It seems that there is more rain this year. " In response to this problem, Ma Xuekuan explained that the rainy season in Northeast China is from the middle and late July to August every year, and it is normal to have heavy rainfall during this period. However, the rainfall varies from year to year, with more or less. At present, it is not obvious that there is too much precipitation in North China this year.
From the night of August 18 to the morning of August 19, Luohe City, Henan Province suffered a torrential rain. Photo by Li Junfeng
Judging from the precipitation anomaly map of recent 10 days, compared with the same period in history, the precipitation in eastern Inner Mongolia and western Northeast China is about 1 times higher than that in previous years, 50% more in eastern North China, and less in most other northern areas. Judging from the precipitation anomaly map in recent 20 days, the precipitation in eastern North China, western Northeast China and eastern Inner Mongolia is relatively high, and most parts of central and western North China are basically flat or less. The precipitation range in northern China in recent 30 days is close to that in recent 30 days, and it is close to normal in general.
"For Beijing, the precipitation in the past 30 days is 20%-30% less; In the past 20 days, the precipitation in Beijing has been flat in the central and western regions and more in the east. In recent 10 days, the precipitation in most parts of Beijing is about 50% more. Therefore, on the whole, since the rainy season, the precipitation in North China and Beijing has been close to normal or slightly less. " Ma Xuekuan said.