There have been nine round of relatively large-scale sandstorm weather in north China since the beginning of spring, far higher than the number in the corresponding period of the previous two years. According to experts China is going to experience another boom of dusty weather in April. What's the exact cause of more dusty weather in China as compared with that of last year? Experts explain the how and why from the following four aspects:

The change of atmospheric circulation is the "major evildoer". The main system that affects the stormy weather in China's northern regions is the Mongolian cyclone in the Baikal Lake region coupled with the Ural high pressure, said professor Li Dongliang at the Cold and Draught Regions Environment and Engineering Research Institute of the Chinese Academy of Sciences. At the beginning of the 21st century the activities of high pressure in Baikal Lake region remained strong, which stopped the southward movement of the northern cold air and which in turn reduced the dusty weather in China. Since 2004 the Mongolian cyclone in Baikal Lake region has grown stronger, which caused the northern cold weather to move south with high frequency. It happens to travel over the dust source region in northwest China, incurring the increase of stormy weathers.

Sudden temperature change is an important cause. Li Dongliang said, if the temperature of the previous winter is relatively low and a sudden warm weather in the following spring it might very well induce dusty weathers. From the 2003 winter to 2004 China experienced a low temperature period. During this period, the temperature in northern Xinjiang, Hexi Corridor of Gansu and Ningxia decreased 1 to 3 Celsius degrees as compared with the normal temperature of the past. In some places witnessed the lowest record-breaking temperature in winter. In the 2004 spring weather in the northwest regions turned warm rapidly and places like Lanzhou even set the highest temperature records. This extremely unstable air current brought about the increase of dusty weather in 2004.

The weakening of the surface heat flux over the Tibet Plateau causes the increase of dust weather. Li Dongliang said the surface heat flux over the Tibet Plateau and the total number of dusty days in north China are of alternate counter-corresponding relationship. That is, when the intensity of the surface heat flux over the Tibet Plateau was especially strong in the previous year dusty weathers in north China will be reduced in the following year. If the surface heat flux is weak it is the other way round. In 2003 the surface heat flux was relatively weak and that caused the increase of dusty weather in most regions of north China in 2004.

This year the dusty weather happens to be at its small cycle of activity. Professor Yang Gensheng, a senior sandstorm expert in China, believes that sandstorm activity has 10 years as a big cycle and 5 years as a small cycle. In 2000 the activity of dusty weather in China was frequent. In 2004 it greets a small cycle. That is why dusty weather is more active than last year.

By People's Daily Online