The large-scale persistent high temperature weather in the south has basically ended, and the high temperature this summer has set a new record
Why is the subtropical high abnormal this summer?
Our reporter Li Hongmei
core reading
At present, the large-scale persistent high temperature weather in the south has basically ended.
The unusually strong subtropical high in the western Pacific is the most direct cause of this summer's high temperature weather.
This is related to the general trend of global warming, but also to factors such as the SST anomaly in the Northwest Pacific on a seasonal scale.
At 18:00 on August 30, the Central Meteorological Observatory lifted the high temperature yellow warning, and the persistent high temperature weather in the south basically ended.
This round of high temperature is the strongest high temperature in comprehensive intensity since complete meteorological observation records began in 1961. The duration, the range above 40 degrees Celsius, and the extremeness have all set new historical records.
This year, the western Pacific subtropical high is unusually strong and is the most direct cause of persistent high temperature weather.
What is a subtropical high?
Why is the subtropical high in the western Pacific so strong this year?
The abnormal subtropical high pressure is the most direct cause of persistent high temperature weather
Recently, the Sichuan Basin, Shaanxi, Chongqing and other places have ushered in continuous heavy precipitation, and the high temperature has finally subsided.
This summer's high temperature and heat wave events started early, lasted for a long time, affected a large area and had a strong comprehensive intensity.
Meteorological monitoring shows: From June 13 to August 30, the regional high temperature event lasted for 79 days, covering an area of more than 5 million square kilometers. High temperatures above 40 degrees Celsius occurred in 23 provinces across the country, and the daily maximum temperature at 366 national weather stations Reach or break historical extremes.
Due to the long duration of high temperature, some rivers dry up during the main flood season.
In the Yangtze River Basin, the water level in many places has reached the lowest level since records began, and Dongting Lake and Poyang Lake "dry" ahead of schedule.
At the same time, high temperature weather also brings various adverse effects on people's production and life, such as surge in electricity demand, decline in hydropower production capacity, obstruction of agricultural production, and forest fires.
Chen Tao, chief forecaster of the Central Meteorological Observatory, said that this year's western Pacific subtropical high has a large range and strong intensity, which is the most direct cause of persistent high temperature weather.
Under its control, the entire southern part of my country is controlled by downdraft airflow, and the sky is clear and less cloudy.
Under the influence of solar radiation during the day, the heating near the ground is intense, and the hot air stays on the ground, which cannot be blown away or dissipated, so a wide range of persistent high temperature weather occurs.
Not only my country, but also in the northern hemisphere this summer, the western Pacific subtropical high, the Atlantic subtropical high and the Iranian high have all intensified in stages, forming a large-scale global warm high pressure belt, and forming high temperature weather in many places in the northern hemisphere.
"The occurrence of high temperature and heat wave events in summer is normal from a climatic point of view. However, the duration, intensity and scope of influence of high temperature and heat wave events in summer have reached super strong levels." Chen Lijuan, chief forecaster of the National Climate Center, analyzed, Persistent atmospheric circulation anomalies are the "culprit" of persistent high temperatures.
This year, the western Pacific subtropical high is abnormally strong and extends westward, reaching the eastern part of the Qinghai-Tibet Plateau on the west side.
At the same time, both the south and north boundaries of the subtropical high have expanded outward, and the area is very large.
In summer, the high temperature events in most parts of southern my country lasted for a long time and ended significantly later than normal.
Powerful subtropical high belt blocks water vapor from low-latitude oceans to the south
What is a subtropical high?
Why is it often seen in high temperature and heat events?
Why is it so strong this year?
Zhang Daquan, senior engineer of the Climate Prediction Office of the National Climate Center, introduced that the well-known subtropical high generally refers to the subtropical high that has a greater impact on my country and is located in the northwestern Pacific Ocean in the northern hemisphere. It exists all year round and is located in the middle and lower layers of the atmospheric troposphere. And less moving warm deep system.
Due to the strong solar radiation in the equatorial region, the atmosphere is heated up and flows to the north and south poles where the temperature is lower.
Under the influence of the earth's rotation, it subsides near 30 degrees north-south latitude, and then the airflow returns to the equator, forming an atmospheric circulation called the Hadley Circulation.
The subtropical high is formed when the airflow sinks in the subtropical region near 30 degrees north and south latitude.
Affected by factors such as the distribution of land and sea, the subtropical high pressure belt in the northern hemisphere splits into several high-pressure cells, namely the North Pacific High, the North Atlantic High, and the Iranian High. Climate has an important influence, and its periodic "jumping north" is directly related to the start and end time of the rainy season and the position of the rain belt in the eastern monsoon region of my country. Abnormal advance and retreat and stable maintenance are important factors leading to abnormal weather and climate in my country.
After the end of the "Meiyu" every year, the main body of the Western Pacific Subtropical High directly controls the middle and lower reaches of the Yangtze River. The downdraft leads to sunny, hot and less cloudy, strong solar radiation, and usually high temperature and drought.
This year, the subtropical high is extremely strong, resulting in continued high temperature and little rainfall in the Yangtze River Basin, which is more and stronger than the normal high temperature and drought.
In terms of influencing factors, on the one hand, it is related to the overall trend of global warming, and on the other hand, it is also related to the thermal anomaly of the Qinghai-Tibet Plateau, the La Niña phenomenon, and the SST anomalies of the Indian Ocean and the Northwest Pacific on the seasonal scale.
This summer, the Qinghai-Tibet Plateau has had a significant heating effect. The South Asian High over the Qinghai-Tibet Plateau is abnormally strong, and the Western Pacific Subtropical High has strengthened its westward extension and opened up with the Iranian High in the western part of the Plateau.
The powerful subtropical high belt blocks the transport of water vapor from the low-latitude oceans to southern my country, and the areas controlled by the subtropical high continue to have high temperatures and little rainfall.
From the perspective of ocean conditions, this summer is in a La Niña state, with abnormally low SSTs in the equatorial and central and eastern Pacific Oceans, and high SSTs in the Western Pacific and South China Seas.
The tropical SST anomaly is conducive to the continued strong and large West Pacific subtropical high through air-sea interaction, resulting in a wide range of high temperature occurrences this year, including Huanghuai, Jianghan, Sichuan and Chongqing.
Raise awareness of adaptation to climate change and actively respond to
Chen Lijuan believes that the extreme characteristics of this year's high temperature events are closely related to the background of climate change.
The sixth assessment report of the United Nations Intergovernmental Panel on Climate Change (IPCC) pointed out that in the context of global warming, changes in many extreme weather and climate events have been observed since the middle of the 20th century, among which the occurrence of high temperature and heat waves is very significant. Characteristics.
"This is a warning for us, reminding us to have a deeper understanding of climate change and improve our ability to adapt to climate change from all aspects." Zhang Daquan said, "In recent years, my country has experienced a lot of problems in agricultural production, flood disasters, architectural design, etc. The ability to deal with climate risks and disaster mitigation and prevention is improving. On the other hand, it is also necessary to increase the awareness of the whole society to adapt to climate change, use climate prediction products to take precautionary measures to deal with climate risks, and strive to minimize social and economic impacts and losses. ."
Experts explained that in the context of climate warming, this summer's high temperature heat wave broke the historical record, with a certain degree of extreme.
However, from the perspective of climate periodicity, due to the self-regulating function of the Earth's climate system, the increase in the probability of extreme events does not mean that the same type of extreme events will occur every year.
On the other hand, with the development of society and economy, the demand for meteorological services in the country and all walks of life is increasing, which requires the meteorological department to further improve the accuracy of forecasting, and at the same time expand the forecast objects downstream, and develop climate services based on disaster risk assessment. Risk prediction, so that decision-making departments and the public can deal with climate change more scientifically and effectively.