Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: Earth knowledge Bureau (ID:diqiuzhishiju), text: cold Night Cold Star, revised manuscript: Koo Hanying, Editor: chestnut, clear

Since May 4, heavy rainfall has occurred in many provinces and regions in southern China, such as Jiangxi, Fujian, Guangdong, Guangxi, Hunan and Guizhou. On May 6, the daily rainfall in Shaowu, Fujian broke the record extreme value of more than 250mm. Jiangxi Yihuang is more than 300mm, equivalent to 1/6 of the average annual rainfall in one day.

(photo: central Meteorological Station) ▼

It has been raining heavily, and floods have followed. 21 rivers in Jiangxi, Fujian and other places have experienced over-warning floods, and 2 rivers have experienced the largest floods since the measured records.

Cities such as Guangzhou and Heyuan in Guangdong, Fuzhou, Ganzhou and Xinyu in Jiangxi, Sanming and Longyan in Fujian have all suffered from waterlogging. Cities have issued guidelines for avoiding waterlogging to their citizens, and countless villages and towns have been threatened by floods. as of May 8, the number of people affected in Jiangxi Province alone has exceeded 500000.

Fuzhou and other places in Jiangxi Province were seriously affected by the disaster.

National Rescue Force Star Night Rescue (Video: CCTV) ▼

Why do Guangdong, Fujian and Jiangxi have such violent torrential rains and disasters at the beginning of summer? Today we will analyze it.

Torrential rain under the duel between cold and warm is high-intensity precipitation, the standard is 24-hour precipitation of more than 50 mm, lasting for many days may cause serious disasters. Compared with other countries, this kind of intensive precipitation is especially common in China, which is directly related to our unique monsoon climate.

From East Asia to South Asia, there is the largest monsoon climate region ▼ in the world.

In the previous East Asian Monsoon region, we mentioned that due to the thermal differences between land and sea (large ocean heat capacity and small land heat capacity, ocean heating and cooling is slower, land heating and cooling is faster) and the seasonal variation of solar direct points, there are East Asian and South Asian monsoons in the western Pacific and the northern Indian Ocean.

East Asian monsoon and South Asian monsoon ▼

In addition, the Qinghai-Tibet Plateau of China has formed a huge area of surface low pressure inland. Drawing the surrounding air inland, this strengthens the summer monsoon, and the scope of the East Asian monsoon is even pulled to Heilongjiang, which is 50 °north latitude, from Pakistan to the largest surface monsoon area of the Heilongjiang River basin. the huge precipitation brought by the monsoon has also become the survival basis of nearly 3 billion people.

The Qinghai-Tibet Plateau is a powerful ▼ for the formation of the East Asian monsoon.

Map of monsoon area ▼

However, the annual precipitation is not uniformly distributed in the whole monsoon area, and there are still great differences in region and time. The "West Pacific subtropical high" on the east side of the monsoon area will bring the warm and humid air from the south to the north and meet with the cold and warm front near the north. The cold air sinks and the warm and humid air rises to form rainfall.

The location of the Western Pacific subtropical high has a great influence on the distribution of rain belts ▼

As the "West Pacific Subtropical High" will move seasonally from north to south, and the accompanying rain belt will also move from north to south, so that all parts of China can precipitation in different periods, and agricultural production can also be arranged accordingly. The precipitation stage of the first flood season in South China is from March to May every year.

It's time to go out with water again, ▼.

But there are also many kinds of precipitation, either continuous rain or high winds and showers. How the frontal rain falls depends on the specific frontal situation.

If the warm and humid air is strong, the warm air mass will actively move to the cold air mass, and a warm front will be formed at this time. There will be continuous precipitation in the warm wind transit, but the intensity is relatively small, and the local temperature rises after the transit.

Warm frontal rain ▼

When the cold air mass is strong, it will actively move to the warm air mass, and the cold air will move faster, and the front will rise sharply and stimulate convection, which will cause gale showers and strong winds to cool down in a short period of time, resulting in strong precipitation weather. After transit, the temperature and humidity will drop.

Cold frontal rain ▼

Judging from the results, the two models have their strengths and weaknesses, but what the southern provinces have encountered recently is neither a cold front nor a warm front, but a "quasi-stationary front."

Hot and dry response under excessive provocation if the cold and warm air masses are equally powerful and the front rarely moves or moves very slowly, there will be a quasi-static front, which is equivalent to stopping on your head and will not go.

When the cold and warm air masses are evenly matched.

The quasi-static front appeared.

(quasi-stationary front diagram, figure: bigmantova) ▼

The slope of the cold and warm front of the quasi-stationary front is very gentle, and the warm air sliding along the front can extend far away from the front, so the cloud and precipitation areas are also very wide. This kind of continuous rainy weather lasts for a long time, but the intensity is also relatively small, as the saying goes, "it rains and does not open for days."

The quasi-static front hangs overhead, and it may be rainy for more than ten days or even a month.

In the two seasons of winter and spring and the end of autumn, the cold air from Mongolia and Siberia weakens until it is blocked by the Nanling Mountains, forming an important weather system affecting South China-the quasi-stationary front.

Several important mountains that distinguish the climate and environment of China

Yinshan is a, Qinling is a, Nanling is a

The position of the quasi-stationary front in South China is also different in different seasons. in the winter half year, the cold high pressure on the north side of the front is strong, so it is located in the south, and the Winter Solstice will even advance to the north of the South China Sea. At this time, under the control of cold air in South China, the precipitation is not very strong.

In the summer half year after the Spring Equinox, the force in the south became stronger, the frontal zone gradually moved northward, and South China entered a long-lasting but low-intensity precipitation process.

The quasi-stationary front in South China will also swing seasonally.

The north side is cold air, and the south side is warm and humid air ▼.

But what is special about this year is that while the quasi-stationary front in South China continues to rain, warm and cold air from the north and south are providing a steady stream of reinforcements to the front.

Since mid-April, extremely hot temperatures of more than 40 ℃ have been seen from Yunnan, Guangxi and Hainan in China to Vietnam, Laos and Thailand on the Indo-China Peninsula, with a record temperature in Vietnam reaching 44.1 ℃. The somatosensory temperature in Bangkok and Phuket in Thailand once reached 54 ℃, while the somatosensory temperature in parts of the Philippines approached 50 ℃.

The temperature difference is huge, but the cold and warm air is stalemated for a time.

Lead to the ▼ of high intensity precipitation on the north side of the quasi-stationary front and frontal line.

However, in the Yangtze River basin, after some precipitation and cooling in Shanghai, Hangzhou, Nanchang and other cities, the temperature on May 7 is still hovering around 20 ℃, 20 °lower than that in Hainan, which is caused by proper cold air.

As a result, the temperature difference between the north and south sides of the "quasi-static front in South China" was too large, but it was stalemated, and a period of "short-term high-intensity precipitation" was forcibly inserted into the "long-term low-intensity precipitation". In the mountainous area of Nanling-Wuyi Mountains, the precipitation intensity is particularly strong. Yihuang, Jiangxi Province, rained 300 mm a day, directly causing a series of flood disasters.

It can be said that you are in the center of the rain belt.

After one day's 300mm, Yihuang's annual average is about 1900mm ▼.

Therefore, whether it is the torrential rain in Jiangxi and Fujian since the 5th, or the strong winds and showers in Guangdong since the 7th, it is actually the result of strong convection in the front line of two extremely strong cold and warm air at the quasi-stationary front.

However, as the sun's direct point continues to move northward and the land heats up rapidly, the cold air in Mongolia and Siberia will become weaker and weaker.

According to the forecast, the South China Sea summer monsoon will break out before May 16, and the southwest current will transport more water vapor from the tropical Indian Ocean and the South China Sea to the East Asian continent, and the convective heavy precipitation in the south will increase significantly. The front of the standoff between cold and warm air will also shift from South China to the Jianghuai region, and the so-called "Jianghuai quasi-stationary front" will generally be formed in June-July, and China's seasonal precipitation will enter the next stage-Meiyu.

The Jianghuai quasi-stationary front forms Meiyu ▼.

However, according to the current forecast of the Central Meteorological Bureau, from the 10th to the 13th, due to the combined influence of cold and warm air, there will be a heavy rainfall process in South China, the central south of the Yangtze River and the south-southwest, mainly heavy to torrential rain, and there will be heavy rain in some areas. The heavy rainfall in South China will continue until mid-May, and it will take some time for it to end completely.

If we look at the cycle of several degrees between cold and summer over a longer period of time, the excessive cold air moving southward this spring and the extreme heat in South China and Indo-China Peninsula may have something to do with the La Nina phenomenon in the "receding process".

As we have said before, the abnormal warming in the eastern Pacific is El Nino, and the abnormal cooling is La Nina. Together, the two and the derived meteorological changes are called the ENSO cycle, which is a long-term interannual variation. Although it is on the other side of the earth, it will also affect the monsoon climate of China through a series of causal chains.

El Nino + La Nina + derived meteorological change, ENSO cycle

This is an age change across the Pacific Ocean.

And China is on the edge of the Pacific Ocean, ▼.

Generally speaking, in La Nina years, cold air activity is relatively more frequent, while La Nina has been going on for three years, which is related to the frequent cold waves and sandstorms from winter to spring this year.

Whether it's a cold wave in winter or a sandstorm in spring

Are all related to the large fluctuations of the westerly belt in the middle latitudes.

The westerly belt is indirectly related to the ENSO cycle in the Pacific Ocean.

(sandy weather from April 9 to 14 this year) ▼

However, whether it is the sandstorm in March or the torrential rain in May, everything will pass. On April 21, the World Meteorological Organization (WMO) said in its Global Climate report 2022 that the abnormally persistent La Nina phenomenon has now ended after three years, and that the tropical Pacific is currently in a neutral warm state of the ENSO cycle, neither El Nino nor La Nina.

La Nina is retreating.

(sea surface temperature in the tropical Pacific from early January 2023 to early March 2023)

(figure: climate.gov) ▼

Predicted ▼ of ENSO probabilities in the next 8 overlapping 3 months

The National Climate Center combines monitoring data, climate models and statistical methods to predict that the equatorial Middle East Pacific will enter a state of El Ni ñ o in the summer of 2023.

El Ni ñ o is the exact opposite of La Nina, and its impact is basically the opposite. According to conventional speculation, we may have to face abnormal weather and meteorological disasters such as warm winter, droughts in the north and floods in the south. The last super strong El Ni ñ o in 2014-2016 led to a new global record in 2016.

Tropical Pacific warms up in summer in the southern hemisphere

El Ni ñ o is the cause of global climate change.

(figure: NOAA) ▼

The abnormal high temperature of the lower surface water in the east-central Pacific Ocean from February to April this year

It indicates that the El Ni ñ o state in this region is coming.

(ocean temperature anomaly map of La Nina phenomenon, figure: NOAA) ▼

But the ENSO cycle has already spawned a variety of unconventional operations, such as the middle El Nino; and the transition from La Nina to El Ni ñ o, which will take time for feedback to affect China; and whether the equatorial eastern Pacific will successfully enter El Ni ñ o?

There are a large number of unknown factors, and it is still extremely difficult to predict the weather a few months later.

If we compare October last year, January and April this year,

You will find that the equatorial eastern Pacific is indeed shifting from La Nina to El Ni ñ o ▼.

In short, due to the characteristics of China's monsoon climate, temperature and precipitation may have a great range of changes, which of the many elements that constitute our climate characteristics may cause great disasters, which shows the importance of meteorological knowledge.

And, with regard to this year's El Nino forecast, we will also publish a special article to interpret it later.

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