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At present, the large-scale sustained high temperature weather in the south is basically over. The extraordinarily strong subtropical high pressure in the western Pacific Ocean is the most direct cause of this summer's hot weather. This is related to the general trend of global warming, and also to factors such as the SST anomaly in the Northwest Pacific Ocean on a seasonal scale.
At 18:00 on August 30, the Central Meteorological Observatory lifted the yellow warning of high temperature, and the large-scale sustained high temperature weather in the south basically ended. This round of high temperature is the strongest comprehensive intensity since the complete meteorological observation record was recorded in 1961, and the duration, range of more than 40 degrees Celsius, and extremes have all set new historical records.
This year's extraordinarily strong subtropical high pressure in the western Pacific Ocean is the most direct cause of persistent high temperatures. What is subtropical high pressure? Why is the subtropical high pressure in the western Pacific Ocean unusually strong this year?
Subtropical high pressure anomalies are the most direct cause of persistent high temperature weather
Recently, the Sichuan Basin, Shaanxi, Chongqing and other places have continuously ushered in heavy precipitation, and the high temperature has finally decreased.
This summer's high temperature heat wave event began early, lasted long, had a large impact and a strong overall intensity. Meteorological monitoring shows that from June 13 to August 30, regional high temperature events lasted for 79 days, covering more than 5 million square kilometers, 23 provinces across the country experienced high temperatures above 40 degrees Celsius, and the daily maximum temperature of 366 national weather stations reached or exceeded historical extremes.
Due to the long duration of high temperatures, 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 in history since the same period of history, and Dongting Lake and Poyang Lake have "dried up" in advance. At the same time, high temperature weather also brings various adverse effects to people's production and life, such as a surge in electricity demand, a 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 subtropical high pressure in the western Pacific Ocean has a large range and strong intensity, which is the most direct cause of sustained high temperature weather. Under its control, the southern part of the continent as a whole is controlled by the sinking air current, and the sky is clear and cloudless. During the day, under the influence of sunlight radiation, the near ground heating is strong, and the hot air is stuck on the ground, which cannot be blown away and cannot be dissipated, so there is a wide range of sustained high temperature weather.
Not only the mainland, but also the northern hemisphere this summer, the subtropical high pressure in the western Pacific, the subtropical high pressure in the Atlantic Ocean and the Iranian high pressure have all been strengthened in stages, forming a large-scale global warm high pressure belt and forming high temperature weather in many places in the northern hemisphere.
"High temperature heat wave events in summer are normal from the perspective of climatic conditions. But the duration, intensity and scope of this summer's heatwave have reached a super level. Chen Lijuan, chief forecaster of the National Climate Center, analyzed that persistent atmospheric circulation anomalies are the "culprits" of persistent high temperatures. This year, the subtropical high pressure in the western Pacific Ocean is unusually strong and abnormally extended westward, reaching the eastern part of the Tibetan Plateau on the west side. At the same time, the southern and northern boundaries of the subtropical high pressure are expanded outwards, and the area is very large. In the summer, the high temperature events in most parts of the southern part of the continent lasted for a long time and ended significantly later than usual.
The powerful sub-high zone blocks the transport of water vapor from the lower latitude oceans to the southern region
What is subtropical high pressure? Why is it often found in high temperature and heat events? Why is it so powerful this year?
Zhang Daquan, senior engineer of the Climate Prediction Room of the National Climate Center, introduced that the well-known subtropical high pressure generally refers to the subtropical high pressure located in the northwest Pacific Ocean of the Northern Hemisphere with a large impact on the mainland, which exists all year round, located in the middle and low layers of the atmospheric troposphere, and is a stable and inactive warm deep system. Due to the strong solar radiation in the equatorial region, the atmosphere is heated and rises, flowing towards the north and south poles where the temperature is lower. Under the influence of the Earth's rotation, it settles near 30 degrees north-south latitude, after which the air flow returns to the equator, forming an atmospheric circulation known as the Hadley circulation. When the air flow sinks in the subtropical region near 30 degrees north and south latitudes, a subtropical high pressure is formed.
Affected by the distribution of sea and land and other factors, the subtropical high-pressure zone in the northern hemisphere is divided into several high-pressure monomers, namely the North Pacific high pressure, the North Atlantic high pressure, and the Iranian high pressure, of which the western section of the North Pacific high pressure - the western Pacific subtropical high pressure has an important impact on the continental weather and climate, and its phased "north jump" is directly related to the rainy season start and end time and the location of the rain belt in the eastern monsoon region of the continent, and abnormal advance and retreat and stable maintenance are important factors leading to continental weather and climate anomalies. After the end of the "plum rain" every year, the main body of the West Pacific Vice High directly controls the middle and lower reaches of the Yangtze River, and the sinking air flow leads to sunny heat and few clouds, the solar radiation is very strong, and there is usually high temperature and drought weather.
This year, the subtropical high pressure is unusually strong, resulting in continuous high temperature and little rain in the Yangtze River Basin, which is more and stronger than the perennial high temperature and drought weather. From the perspective of influencing factors, on the one hand, it is related to the overall trend of global warming, on the other hand, it is also related to the thermal anomaly of the Qinghai-Tibet Plateau, the La Niña phenomenon and the sea temperature anomaly of the Indian Ocean and the northwest Pacific Ocean on the seasonal scale.
This summer, the heating effect of the Qinghai-Tibet Plateau is remarkable, the south Asian high pressure over the Qinghai-Tibet Plateau is abnormally strong, and the western sub-high strengthens the westward extension and opens up with the Iranian high pressure in the western part of the plateau. The strong sub-high zone blocks the transport of water vapor from the low-latitude ocean to the southern part of the continent, and the sub-high control area continues to be hot and rainy. Judging from the ocean conditions, this summer is in La Niña state, the equatorial Middle East Pacific Ocean SST is unusually low, the Western Pacific Ocean and the South China Sea SST is high. Tropical SST anomalies through the interaction of sea and air are conducive to the continuous strength and largeness of the Western Pacific Sub-High, resulting in a wide range of high temperatures this year, including Huanghuai, Jianghan, Sichuan-Chongqing and other places.
Raise awareness of adaptation to climate change and respond proactively
Chen Lijuan believes that the extreme characteristics of this year's high temperature events are closely related to the background of climate change.
According to the sixth assessment report of the United Nations Intergovernmental Panel on Climate Change (IPCC), many changes in extreme weather and climate events have been observed since the middle of the 20th century in the context of global warming, of which the frequency of high temperature heat waves is a very significant feature.
"This is a warning for us to have a deeper understanding of climate change and to improve our ability to adapt to climate change in all aspects." Zhang Daquan said, "In recent years, the mainland's ability to cope with climate risks and reduce disasters and prevent disasters in agricultural production, flood disasters, architectural design and other aspects has been improved. On the other hand, however, we should also raise awareness of the adaptation of the whole society to climate change, use climate prediction products to deal with climate risks in advance, and strive to minimize socio-economic impacts and losses. ”
Experts explained that in the context of climate warming, this summer's high temperature heat wave broke the historical record and has a certain extreme. However, from the perspective of climate cyclicality, because the Earth's climate system has a self-regulating function, 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 social 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, while expanding the forecast object to the downstream, and developing climate risk prediction based on disaster risk assessment, so as to facilitate decision-making departments and the public to respond to climate change more scientifically and effectively.
Source: People's Daily