Characteristics Of Spatial And Temporal Variation Of Frozen Soil In China And Their Association With The East Asian Climate

Based on the quality control of daily meteorological observation data of frozen soil in China, the data which have the length of 40 years is chosen. The spatial and temporal variations of frozen soil have been investigated also same as the trends of frozen soil in the background of global warming. Meanwhile the three regions: the east china, the northwest china, and Qinghai-Tibet Plateau in accordance with their different characteristics of frozen soil were analyzed. Then the relationship between frozen soil and the summer precipitation in china, associated the circulations anomalies is studied. The main results are as follows:1. The results show that frozen soil occurs in large parts of the territory in China, in the eastern china from the Daxin'anling mountain to the Yangtze River, and in some particular years frozen soil extended to Zhejiang, Hunan and Fujian provinces. There is also widely distribution of frozen soil over Northwest China and Qinghai-Tibet Plateau. In the eastern of china, distribution with the latitude zonal is the main performance of the frozen soil, and in Qinghai-Tibet Plateau, the main performance of the frozen soil is distributed with the vertical zonal. The northwest have all of the distribution.2. The monthly variation of seasonal frozen soil is significant. The freezing process generally began in September, and then reached the maximum of depth and area in the end of winter. The depths of frozen soil is exceeding 100 cm and even 200cm in some parts of the Northern China and Qinghai-Tibet Plateau. In spring the frozen soil began to thaw and finished in the summer. The Daxin'anling mountain and Qinghai-Tibet Plateau have the longest length of the freeze, it lasted for more than half a year, and the freezing time is shorter in the Yangtze River and the Huaihe River Valley, only about two or three month.3. In the background of global warming in past few decades, the frozen soil showed a degradation in China. The maximum of frozen depth decreased, the beginning dates of soil freezing occurred later and the ending dates of soil freezing occurred earlier and the persisting of soil freezing shortened, as well as the soil base arisen. It is in the mid 1980's that the significant abrupt change of the frozen soil happened.4. It is found that there is a significantly negative correlation between the frozen soil and summer precipitation in the southeast of China. In early spring, the anticyclone centered in the Mongolia plateau in the Eurasia occurs according to the strong frozen soil. Meanwhile the anomalous northerlies prevail from the middle latitudes of East Asia to the south china throughout northeast of China. These anomalous circulations may continue to the following summer and weaken East Asian Summer Monsoon. These circulation anomalies are related to the above than normal precipitation in the southeast of China. Moreover, the strong frozen soil is followed by increased ascending vertical velocity, specific humidity, which provide necessary water vapor conditions for increasing the summer precipitation in the southeast of China, and vice versa. The soil variation provides a potential valuable signal for predicting the summertime precipitation in the southeast of China.