青藏高原隆升与欧亚内陆及北非的干旱化

通过利用一个较为完善的大气环流模式(GCM)进行了一系列青藏高原不断隆升的数值模拟试验结果.共进行了11个改变地形高度的数值试验,即对欧亚大陆上现代大地形所在地区(约10～60°N,50～140°E)陆地上所有格点的地形高度分别取为现代地形高度值的100%,90%,80%,70%,…,10%,外加一个无地形试验MOO,共完成了11个试验.结合与干旱化有关的地质记录,探讨了高原隆起在欧亚内陆及北非干旱演化过程中的作用.结果表明,仅仅改变高原地区地形高度的数值试验结果与气候变化地质记录在趋势上有可比性,青藏高原隆升是中亚及北非地区在地质时间尺度上干旱化加剧的重要原因,但却不是上述干旱区形成的根本原因.

TIBETAN PLATEAU UPLIFT AND DRYING IN EURASIAN INTERIOR AND NORTHERN ARFICA

Drying is one of the most devastating natural disasters. Drying usually occurred in the margins of arid areas because of the ecological fragility in those regions. According to the world distribution map of arid regions developed by UNESCO, the most severe and vast arid regions include northern Africa and Eurasian interior. The research on identifying the primary factor in this drying process is undoubtedly important both scientifically and practically. In past studies, many digital modeling experiments have revealed that the Tibetan Plateau uplift has made important contribution to the formation of the drying climate in mid-latitude. The digital simulation results used in this paper were obtained by Liu X D and Jiao Y J in their recent finished series experiments on continuous uplift of Tibetan Plateau. The applied digital model is the global general circulation model (GCM) (R15 L9) developed by center for ocean-land-atmosphere studies (COLA). In the experiments, we changed the altitude to 100%, 90%, 80%, 70%, …, 10% of its modem topography in all the grids of modern Eurasian continent region (around 10- 60°N, 50-140°E). These runs are named M10, M09, M08, M07, …, M01, respectively. With 1 additional no-topography experiment M00, which takes the altitude value to 200m where modem topography value is higher than 200m and keep the values unchanged whereas altitude is less than 200m. Thus, there are altogether 11 experiments having been done. The results of these digital experiments may reflect the Plateau uplift effects on the variations of atmospheric circulation and climate, since the experiments only change the altitudes of the plateau while the other boundary conditions has been kept the same with those of the present. The analysis of precipitation and soil moisture changes associated with drying has shown that total precipitation in Asian monsoon regions increases along with the gradual uplift of the Tibetan Plateau. On the other hand, continuous rain belt in mid-latitude break up with decreased precipitation. Soil moisture is the results of moisture balance and is superior to precipitation in reflecting aridity changes. Differences of annual mean soil moisture at different stages of plateau uplift in the experiments suggest that the uplift of Tibetan Plateau, especially the later uplift could be the essential cause for the formation of arid region in the northwestern China interior. In general, the digital simulation has shown that the intensification of drying in mid-Asia and northern Africa had been caused primarily by the Tibetan Plateau uplift. Geologic records, such as the eolian sedimentation rare in central Loess Plateau and stable isotopic evidence in soil carbonate from eastern Africa also confirmed the drying trend since 4 MaB.P. From the above digital simulation and geologic evidence, qualitative conclusion could be reached that central Asia and northern Africa had undergone long process of drying primarily caused by Tibetan Plateau uplift. The degree of drying varies with the different stages of uplift and intensified dramatically in the later uplift. It is indispensable to integrate the research of modeling simulations and geologic observations while exploring the climate variation and its mechanism involved. In the text, geologic evidence had clarified the facts of drying in central Asia and northern Africa and the uplift events of Tibetan Plateau. However, geologic observations could not reveal the causality in the process. On the other hands, modeling experiments results of changing topography of the Plateau could not offer any information comparable to geological ages. The experiments can only provide us with the information that the uplift may induce the drying in central Asian and northern Africa. It would be more meaningful if we take the above two approaches together. The trend of simulation results correlate with the climate variations evidenced by geologic records. It indicates that plateau uplift may be the primary cause of drying in above regions. Judging the results of digital simulati