Spatio-temporal Variation Of Ground Temperature And Atmospheric0℃Isotherm Height In Summer During The Past50Years In Northwest China

Based on the meteorological information from112surface observation stationsand21air sounding stations during1960-2009, and using the method of InverseDistance Weighted, Mann-Kendall and Wavelet Analysis, the spatial and temporalvariation of the0℃isotherm height and mean temperature, in Northwest China anddifferent regions in the area, as well as the relevance between the0℃isotherm heightand mean temperature was discussed in order to investigate some features. The papergot the results as follows:（1） In50years, the temperature in this area increased and the mean temperaturein summer is18.93℃, which increased0.20℃per10years. The tendency of variationin temperature is opposite during the climatic transition: it decreased before1987, butincreased after that year. The mean temperature in summer increased temporally inmost regions, especially in the eastern Tianshan and Altun Mountains, the extent ofwhich ranges between0.3℃·（10a）^-1and0.9℃·（10a）^-1, while it showed significantlydecreasing in Qinling-Daba mountains and Urumqi. After1987, the averagetemperature, in most areas, raised obviously in summer. The Xinjiang and Shaanxishowed a significant difference from south to north. The variation in Monsoon regionof eastern China and arid region of northwestern China, which changed in1997, isalike to the region of Northwest China. The mean temperature in Northwest Chinaexisted an oscillation cycle between5and13years, which has a primary cycle of5years. The Monsoon region of eastern China and the Tibetan Plateau region bothexisted an oscillation cycle of5,8and13years, while the arid region of northwesternChina has the cycle of5,13and16years.（2） Since1960, the average0℃isotherm height is4675.7m. Overall, it showeda decreasing trend at early stage and then reached a higher level, with a increasing rateat2.6m per year after1987. The0℃isotherm height in Tibetan Plateau region is thehighest, the second one is the monsoon region of eastern China, while the arid regionof northwestern China is the lowest. Spatially, the0℃isotherm height has a highvalue center near Urumqi. The0℃isotherm height in the middle region of NorthwestChina remarkably increased, the tendency of climatic variation ranges between0.0m·a-1and2.0m·a-1. On the contrary, it decreased in the western and eastern part of Northwest China. From the year of1987, the0℃isotherm height in most areas ofNorthwest China raised obviously, especially in the region of eastern Xinjiang,northern Qinghai, and northern Shaanxi.（3） The0℃isotherm height in Northwest China has an oscillation cycle that isthe same as the arid region of northwestern China and the Tibetan Plateau region, of5,8and13years, the primary cycle of which is13years. The monsoon region of easternChina existed a cycle of5,8and15years.