What effects did the uplift of the Qinghai-Tibet Plateau have on the Asian monsoon climate?

The Qinghai-Tibet Plateau occupies about a quarter of China's land area, with an average elevation of over 4,000 meters. It is the plateau with the highest altitude and the most complex terrain in the world, and occupies an important position in the plateau and alpine areas of the world. Some people call it the "roof of the world" of the earth.

The crustal movement since Tertiary has led to the retreat of the ancient Mediterranean and the rise of the Himalayas. In Pliocene, 654.38+million years ago, the average elevation of Qinghai-Tibet region was about 654.38+0000 meters, with the natural landscape of tropical and subtropical forests and forests and grasslands. Later, the whole region rose sharply and distinctly, which opened an important chapter in the natural history of the Qinghai-Tibet Plateau. Because the Qinghai-Tibet Plateau is located in the subtropical zone, the air over the plateau sinks in winter and rises in summer, which plays a role in discharging and pumping air to the surrounding atmosphere, regulating seasonal changes and enhancing the East Asian monsoon. Abnormal thermal conditions on the Qinghai-Tibet Plateau can induce abnormal subtropical high activity, which is an important factor affecting climate anomalies in China and the world, and has an extremely important impact on the evolution of atmospheric circulation in China, Asia and even the northern and southern hemispheres, and directly affects the formation and evolution of weather and climate such as drought and flood in China.

The uplift of the Qinghai-Tibet Plateau has greatly changed the atmospheric circulation in China and even the whole of Asia. Before the uplift of the Late Tertiary Plateau, the planetary wind system was dominant, and the westerly wind prevailed in China. The uplift of the Qinghai-Tibet Plateau forced the westerly belt to retreat northward, and a powerful Mongolian-Siberian high was formed in the north. In winter, the Mongolian-Siberian high will be hit by cold waves every once in a while. In the process of the cold wave going south, when it was blocked by the Qinghai-Tibet Plateau, it turned east and directly drove North China and even South China, making the temperature in the eastern part of China lower than that in other parts of the world at the same latitude. Due to the great uplift of the Qinghai-Tibet Plateau, the Himalayas have become the main obstacle to prevent the Indian Ocean from moving northward, making the climate in the area north of the Himalayas, especially in the northern Tibet Plateau, dry and rainy. This change affects the whole northwest region.

According to the research of meteorologists, if there is no Qinghai-Tibet Plateau, the southwest monsoon airflow will not exist, the continental climate in Qinghai-Tibet will become more and more obvious, and the climate will become more monotonous. This area will be located in subtropical and temperate forest grassland-grassland-desert zone. However, due to the uplift of the Qinghai-Tibet Plateau, the thermal and dynamic effects of the plateau topography have changed the atmospheric circulation situation in the Qinghai-Tibet Plateau and its surrounding areas, thus dominating many characteristics of the Asian monsoon. The seasonal variation of cold and heat sources in the plateau forms a unique plateau monsoon phenomenon, which maintains and strengthens the East Asian monsoon and causes the branch of westerly airflow, which has an important impact on the formation and maintenance of arid climate in northwest China. All these have had a far-reaching impact on the natural geographical environment in East Asia, especially in China. If we compare the Qinghai-Tibet Plateau and its surrounding lowlands, we can see the significant differences in natural landscape between them. Assam Plain in India in the south of Qinghai-Tibet Plateau is a humid tropical evergreen rainforest area, while its north is an extremely arid temperate desert in Central Asia. The eastern edge of the plateau is adjacent to the subtropical moist evergreen broad-leaved forest belt, and the western side is adjacent to the subtropical semi-arid forest grassland and shrub grassland belt. Located in the hinterland of the Qinghai-Tibet Plateau, which is the center of the disparity between the north and the south and the east and west, it has a unique natural history, formed a unique plateau landscape and attracted people's attention. At the same time, the Qinghai-Tibet Plateau is not flat, with high mountains and dense valleys. These complex small topography will produce some small-scale circulation circles, which will not only affect the local climate, but also interfere with the large-scale airflow.

Without the Qinghai-Tibet Plateau, most of the subtropical areas of our country would be deserts, and the present climate would not be formed. The average height of the Qinghai-Tibet Plateau is 4500 meters above sea level. If there is no plateau at this height, its temperature will be very low. Usually, the altitude of more than 4000 meters should be MINUS 10 degrees Celsius, but the climate of the Qinghai-Tibet Plateau is similar to that of Beijing, and it is warm without cotton-padded clothes during the day. This unique geographical condition forms a special plateau monsoon climate, induces the southern monsoon and promotes the formation of the East Asian monsoon. These two monsoon climates make the whole subtropical region of China have a very humid climate, and the water vapor on the edge of the Qinghai-Tibet Plateau is continuously transported to the plateau along this passage, resulting in very humid areas on the edge of the Sichuan Basin, including the Yarlung Zangbo River Grand Canyon, and its water vapor transport capacity is equivalent to the total amount transported from Jiangnan to Jiangbei in summer. Nujiang River and Yarlung Zangbo River are two main water vapor transport channels.

Without the Qinghai-Tibet Plateau, the altitude of China at 23.5 degrees north latitude and 4,500m above sea level would be minus 10 degrees Celsius. Now the Qinghai-Tibet Plateau is very warm in the daytime. In this area of 2.5 million square kilometers, it turns a huge heat source into the atmosphere, and a large amount of hot gas rises to form thermal high pressure. This special plateau monsoon climate induced the West Indian Ocean monsoon. The two monsoon climates make the Sichuan Basin in China wet and rainy, which enables the Yarlung Zangbo River, Nujiang River and Jinsha River to transport a lot of water resources. Therefore, the forest on the highest plateau in the world is very dense, with the largest virgin forest in China at present. Below the forest are large bushes, and then grass. The animal and plant ecosystems here have adapted to the ecological environment of the plateau. They are one of the few and most important treasures of ecological resources preserved by human beings so far.

According to the zonality law of geography, the middle and lower reaches of the Yangtze River in China should be arid and desert areas. However, due to the formation of the Qinghai-Tibet Plateau, the pressure gradient between the ocean and the mainland is greater, attracting a large amount of water vapor to land in summer, and the climate is warm and humid, making it the most typical monsoon climate zone in the world. Otherwise, the middle and lower reaches of the Yangtze River will be as barren as North Africa where Cairo is located. In fact, the study found that the area around China, Hubei and Jiangxi was once a desert landscape 20-30 million years ago, but the Qinghai-Tibet Plateau became moist after the uplift, which also promoted the formation and strengthening of the Siberian-Mongolian high, which made the northwest of China more arid, the winter wind became very strong, and aeolian loess began to accumulate on the Loess Plateau.