By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations revealed by the reconstruction indicate that there were four periods to have average tem- peratures similar to or even higher than that mean of 1970 to 2000 AD. A particularly notable rapid shift from cold to warm, we call it the "Eastern Jin Event", occurred from 348 AD to 413 AD. Calculation re- sults show that the temperature variations over the mid-eastern Tibetan Plateau are not only repre- sentative for large parts of north-central China, but also closely correspond to those of the entire Northern Hemisphere over long time scales. During the last 2485 years, the downfall of most major dynasties in China coincides with intervals of low temperature. Compared with the temperature records in other regions of China during the last 1000 years, this reconstruction from the Tibetan Plateau shows a significant warming trend after the 1950s.
基于标准化后的高分辨率气候代用资料,应用高阶矩分析方法检测近2000年来气候极端异常演变特征;同时结合滤波方法进行具有物理背景的层次分离,进而研究了各时间层次气候极端异常变化信息及其贡献.结果表明:1)在100年以上的时间层次上,可能存在千年左右的气候变化振荡周期,而且20世纪是近2000年来气候极端异常现象最为活跃的时段,可能对应于气候极端异常现象活跃期.2)对于20—60年这一时间层次,公元300—1100年间气候极端异常现象比较明显,而公元1100—1980年间相对比较缓和;该层次对20世纪的气候异常没有显著贡献.世纪以上和20—60年时间层次均揭示出在近2000年的气候变化中,公元1100年前后可能是一个气候极端异常现象演变的关键转折时期.3)在年际尺度上(小于20年),北京石花洞石笋微层厚度时间序列中发生气候极端异常现象的年份与出现E1Ni o事件和La Ni a事件的年份有非常好的对应关系(仅讨论公元1960—1980年).4)高阶矩分析方法对于检测气候极端异常分布及演变规律有较好的应用前景.
By using the regional climate model (RegCM_NCC), East Asian monsoon andprecipitation over China during 1998 to 2002 are simulated. Results show that the model can wellreproduce the seasonal patterns of mean circulation as well as the intensity and seasonal march ofthe East Asian monsoon. The simulated onset or retreat time of the West Pacific subtropical high,and the intensity and location of the South Asian high are consistent with the fact. The spatialdistribution and transport of moisture in lower layer are also well simulated. The seasonalvariations of regional rainfall and temperature are reproduced in the model, with three northwardshift time and intensity of the rain belts over the sub-regions (such as Mid-Lower Yangtze basinsand South China) well corresponding to the observation. However, the simulated summer monsoon isstronger compared with NCEP reanalysis fields, with the location of subtropical high being furthernorth by 2-3 degrees than normal. Error evaluation shows that there is a discernible systematic biasin the simulated mean circulation pattern, with air temperature bias being positive over the landand negative over the ocean in the lower troposphere in summer. The systematic bias exaggerates thesummer temperature difference between the land and ocean, which may be a main responsible factor forthe stronger simulated summer monsoon, thus resulting in the overestimated rainfall in North Chinaand it can not reflect well the abnormal rainfall distribution in these 5 years. The deficiency maybe mainly contributed to the complex topography and cloud-radiation parameterization scheme. Theanalyses also indicate that it is difficult to simulate the persistent abnormal precipitationpattern over China. It is necessary to improve the model's capability further.
