The accumulated temperature in the north of Bulian Mountain is much higher than in the south. What is the reason?

The Qilian Mountains, located in the northeastern part of Qinghai Province and the western border of Gansu Province in China, are one of the main mountain ranges in China. It consists of a number of parallel mountains and wide valleys running northwest to southeast. Because it is located on the south side of the Hexi Corridor, it is also called Nanshan. It is 800 kilometers long from east to west, 200 to 400 kilometers wide from north to south, and has an altitude of 4,000 to 6,000 meters. It has 3,306 glaciers and an area of ??about 2,062 square kilometers. The Qilian Mountains are located in the mid-latitude north temperate zone, deep inland and far away from the ocean. It is also located at the intersection of the three major plateaus: Qinghai-Tibet, Mongolia-Xinjiang, and Loess. Due to the special influence of the Qinghai-Tibet Plateau on atmospheric circulation, the moist airflow from the southeast monsoon in summer can extend from north to west. In winter, affected by the cold dry air in Inner Mongolia and the cold airflow from the northwest, this area has a large cooling rate and large temperature changes in winter. In summer, there are more clouds and more precipitation, which offsets the influence of latitude. As a result, there is no obvious difference in sunshine hours from April to August, and April is even longer than July. After entering winter, although the sunshine hours are relatively shortened, due to Controlled by the Mongolian high pressure, the climate is cold and dry, with mostly sunny and low-temperature weather. Therefore, the sunshine hours in winter change less than the sunshine hours in summer. Therefore, its changes within the year show inconsistency with the changes in available light time. A relatively stable temperature space is formed on the north slope, which is located on the south side of the Hexi Corridor and on the edge of the Tarim Desert fracture platform. Affected by the climate of the Qinghai-Tibet Plateau and the desert climate, the accumulated temperature is higher than that of the south slope.