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991.
992.
Seasonality changes in China under elevated atmospheric CO 2 concentrations were simulated using nine global climate models,assuming a 1% per year increase in atmospheric CO 2.Simulations of 20th century experiments of season changes in China from the periods 1961 80 to 1981 2000 were also assessed using the same models.The results show that the ensemble mean simulation of the nine models performs better than that of an individual model simulation.Compared the mean climatology of the last 20 years in the CO 2-quadrupling experiments with that in the CO 2-doubling ones,the ensemble mean results show that the hottest/coldest continuous-90-day (local summer/winter) mean temperature increased by 3.4/4.5°C,2.7/2.9°C,and 2.9/4.1°C in Northeast (NE),Southwest (SW),and Southeast (SE) China,respectively,indicating a weakening seasonal amplitude (SA),but by 4.4/4.0°C in Northwest (NW) China,indicating an enlarging SA.The local summer lengthened by 37/30/66/54 days in NW,NE,SW,and SE China,respectively.In some models,the winter disappeared during the CO 2-quadrupling period,judging by the threshold based on the CO 2-doubling period.The average of the other model simulations show that the local winter shortened by 42/36/61/44 days respectively,in the previously mentioned regions. 相似文献
993.
994.
995.
We have investigated non‐Darcian flow to a vertical fracture represented as an extended well using a linearization procedure and a finite difference method in this study. Approximate analytical solutions have been obtained with and without the consideration of fracture storage based on the linearization procedure. A numerical solution for such a non‐Darcian flow case has also been obtained with a finite difference method. We have compared the numerical solution with the approximate analytical solutions obtained by the linearization method and the Boltzmann transform. The results indicate that the linearized solution agrees generally well with the numerical solution at late times, and underestimates the dimensionless drawdown at early times, no matter if the fracture storage is considered or not. When the fracture storage is excluded, the Boltzmann transform solution overestimates the dimensionless drawdown during the entire pumping period. The dimensionless drawdowns in the fracture with fracture storage for different values of dimensionless non‐Darcian hydraulic conductivity β approach the same asymptotic value at early times. A larger β value results in a smaller dimensionless drawdown in both the fracture and the aquifer when the fracture storage is included. The dimensionless drawdown is approximately proportional to the square root of the dimensionless time at late times. 相似文献
996.
Shuhuan Du Baosheng Li Dongfeng Niu David Dian Zhang Xiaohao Wen Deniu Chen Yi Yang Fengnian Wang 《Chemie der Erde / Geochemistry》2011,(1):87-95
The MGS5 segment of the Milanggouwan stratigraphical section in China's Salawusu River Valley records 8.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and paleosols. Based on a comprehensive analysis of the distribution of Rb and Sr within the segment and paleoecological evidence (fossils), it appears that the observed sedimentation cycles mainly resulted from fluctuations between dry-cold and warm-humid climates, which indicates that the MGS5 segment experienced at least eight cold-dry and nine warm-humid climatic fluctuations. Of these, 12 cold–warm climate fluctuations correspond to DO20–DO25 and stadia 21–26 recorded by the NGRIP ice cores. Another five cold–warm climatic fluctuations that occurred during MGS5e correspond to five substages (5e1–5e5) recorded by the GRIP ice cores from Greenland. This kind of high-frequency climatic fluctuation on a kiloyear scale was mainly subject to variations in the strength of the East Asian winter and summer monsoons. 相似文献
997.
998.
越南西北部大象山超高温变质岩的发现及其区域构造意义 总被引:1,自引:1,他引:0
越南西北部大象山群孔兹岩系中发育一套含刚玉+尖晶石+石榴石+夕线石组合的富铝岩石块体,它们呈透镜状包体形式赋存于孔兹岩系内。岩石中刚玉+尖晶石+石榴石+夕线石组合的发育指示岩石经历了超高温变质作用的改造。其中尖晶石和石英的共生组合表明了变质温度高于900℃,而利用岩石退变质矿物组合中的黑云母-石榴石温度计,黑云母-斜长石-石榴石-石英组合温度-压力计估算的变质温度压力条件分别为879~917℃、0.90~0.94GPa。岩石中的早期刚玉+夕线石的组合的存在说明岩石变质作用已经从高角闪岩相进入到了麻粒岩相;而峰期变质矿物组合尖晶石+石英的出现,指示了变质温度高于900℃的超高温变质作用。另一方面,退变质过程中钛铁矿的发育表明岩石经历了快速抬升降压的过程。变质作用的P-T轨迹分析揭示出岩石经历了早期同步升温增压后的快速增温达到峰期条件,后经历快速等温减压过程。这种温压条件的变化与板块会聚过程中由于俯冲板片的断离而使软流圈上涌造成热异常的温压条件变化基本一致。通过对超高温变质岩石进行锆石SIMS U-Pb测年获得的结果大于58Ma,推测这次超高温变质与喜马拉雅运动中印度与欧亚大陆的初期会聚-碰撞作用相关。 相似文献
999.
1000.
叠前时间偏移已经成为地震资料处理的常规手段之一,在构造复杂但速度横向变化不大时,应用克希霍夫叠前时间偏移方法,一般可以得到较好的成像效果。但是叠前时间偏移是一项系统工程,一些配套技术的选取和一些关键参数的选取,直接影响到成像结果。这里根据O-MEGA2处理系统制定的叠前时间偏移的处理方法和流程,对叠前时间偏移处理的配套技术和关键参数(叠前道集偏移距分组、偏移孔径和倾角选取、均方根速度建模、旅行时算法)进行了分析总结,结合试验程序进行了研究和讨论,并提出了关键参数选取的基本原则,对实际处理工作具有一定的应用价值。 相似文献