Hot, hot, hot! When will the high temperature end?

Recently, the heat wave and hot weather have made many people miserable. Especially in the southern region, the hot and humid feeling makes people feel like they are in a steamer. As soon as they go out, they sweat profusely and have to hide in the air-conditioned room to cool down.

This year, the heat came early and became intense. What exactly caused this situation? When will the high temperature end? Let's listen to the authoritative interpretation of the National Climate Center.

900 million people affected by high temperatures

According to the National Climate Center, my country has been experiencing continuous high temperatures in recent days. The high temperature event has lasted for more than 30 days, affecting more than 900 million people. In June this year, the global average temperature was about 0.4℃ higher than usual, the highest since 1979.

As of July 12, some cities have experienced high temperature days for more than a month, such as Luohe, Henan (33 days), Huaxian, Shaanxi (31 days), Shanshan, Xinjiang (36 days), Naomaohu (33 days), and Turpan and Toksun, Xinjiang, even reaching 42 days.

Compared with the same period in previous years, the number of high-temperature days in the above-mentioned areas is generally 5 to 10 days more, among which Henan, Hubei, Shaanxi, Anhui, Shandong, and parts of Jiangsu have more than 10 days. It can be said that these areas are much hotter this year than in previous years.

At the same time, the extremes of high temperatures were also stronger than in previous years. A total of 71 national meteorological stations across the country recorded record high temperatures, including Lingshou (44.2°C), Gaocheng (44.1°C), Zhengding (44.0°C) in Hebei Province, and Yanjin (44.0°C) in Yunnan Province, where the daily maximum temperatures reached above 44°C.

Distribution of extreme maximum temperatures across the country from June 13 to July 12, 2022. Image source: National Climate Center

Since the beginning of the 21st century, the typical years of large-scale continuous high temperature events in my country include 2003, 2013, and 2017. Overall, this year's high temperature event started earlier than the above years, but at present, the duration and the number of historical extreme value stations are not as long as those three years, and the affected area and the highest temperature at a single station are not as long as those in 2017, but have exceeded those in 2003 and 2013.

Global warming and abnormal atmospheric circulation

The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) of the United Nations pointed out that in the past 50 years, global warming has been occurring at an unprecedented rate since the past 2000 years. This is the climate background for the frequent occurrence of high temperature heat waves in the Northern Hemisphere. Abnormal atmospheric circulation is the direct cause of the frequent occurrence of high temperature heat waves in many parts of the world since June.

Since June this year, the western Pacific subtropical high-pressure belt, the Atlantic high-pressure belt and the Iranian high-pressure belt have all strengthened in stages over the subtropical region of the Northern Hemisphere, thus forming a large-scale global warm high-pressure belt.

Image source: CCTV News

Under the control of the warm high-pressure belt, the prevailing downward airflow is conducive to ground warming. In addition, under the influence of the large-scale high-pressure belt, the air is relatively dry and clouds are not easy to form, which also makes it easier for solar radiation to reach the ground, resulting in frequent and strong high temperatures, which in turn causes continuous high temperature heat waves in many places in the Northern Hemisphere.

Specifically in my country, the ongoing La Niña phenomenon has provided important climatic background conditions for the occurrence and development of high temperatures in the south since June this year, especially the strengthening of the mid-latitude warm high-pressure belt in July, which led to the occurrence of high temperature weather over a large area.

La Nina, also known as the anti-El Nino phenomenon, refers to the abnormal cooling of the sea water in the eastern and central equatorial Pacific Ocean. La Nina began to appear in the tropical Pacific Ocean in October last year, and this year's La Nina phenomenon has significantly weakened around April, but the atmosphere still has a lag effect.

According to statistical analysis, in the summer of the year following the occurrence of most La Nina phenomena, the western Pacific subtropical high pressure (hereinafter referred to as the subtropical high pressure) tends to move northward. Since late June this year, the subtropical high pressure has moved northward, especially after Typhoon Siamba moved northward in early July, the subtropical high pressure strengthened and extended westward, the Iranian high pressure extended eastward, and combined with the mid-latitude continental high pressure, forming a stable warm high pressure belt over my country, which in turn caused a large range of high temperature weather.

In addition, the water vapor carried by the subtropical high causes higher humidity in central and eastern my country, making the perceived temperature higher.

When will the high temperature end?

When will the high temperature ease? There are two ways to cool down in summer: typhoons and rainfall, especially the frequent thunderstorms in the afternoons. At present, there is no news of typhoons that may land in my country, and large-scale cooling is still a long way off. However, once the subtropical high pressure weakens, the probability of local thunderstorms will greatly increase, and it is still possible for some places to enjoy a brief coolness.

We need to remind you that according to the forecast of the Central Meteorological Observatory, after the 21st, high temperatures in southern China will develop again and expand in scope. The daily maximum temperature in Fujian, Jiangxi, southern Zhejiang and other places can reach 39 to 41 degrees Celsius. The National Climate Center also predicts that in the next 15 to 30 days (July 27 to August 11, 2022), the temperature in most parts of my country will be higher than the same period of previous years, and there may be a long-lasting high temperature weather process. It is necessary to prevent the adverse effects of high temperature heat waves on people's production and life and power supply.

This article is produced by Science Popularization China, produced by Ye Haiying (Meteorological Publicity and Science Popularization Center of China Meteorological Administration), and supervised by China Science Popularization Expo