末次盛冰期百年尺度气候变化的南京石笋记录   总被引：17，自引：10，他引：17       下载免费PDF全文

汪永进  孔兴功  邵晓华  吴江滢 《第四纪研究》2002,22(3):243-251

据年层计数和TIMSU系测年结果,建立了南京汤山葫芦洞YT石笋年际精度时间标尺(18000～14000aB.P.)。除石笋顶部5mm层段外,高分辨率的^δ18O、灰度和年层厚度3种指标在百年尺度上具有相当一致的对应关系,表明这3种指标对气候因素变化响应比较敏感。综合石笋^δ18O和本区古植被资料,估计末次盛冰期和波令暖期年均温分别达7℃和15℃。石笋揭示的末次盛冰期气候可进一步划分为4个阶段:1)18150～16900aB.P.,年均温和洞穴湿度逐步下降;2)16900～16100aB.P.,年均温和洞穴湿度相对稳定,可进一步划分为3个暖峰和两个冷谷;3)16100～15600aB.P.,年均温快速下降,按氧同位素平衡方程计算,其冷谷可能接近于0℃,但洞穴湿度比前期下降幅度并不大;4)15600～14750aB.P.,年均温和洞穴湿度比较稳定。这种气候演化的阶段性和突变性与北大西洋地区气候记录可以对比,反映极地与东亚季风气候受共同的驱动机制支配。从石笋4种指标(^δ18O、^δ13C、灰度和年层厚度)的功率谱图中识别出不同尺度的太阳活动周期成分,其中80aGleissberg周期特别显著,表明末次盛冰期边界条件下太阳活动仍是短尺度气候变化的主要驱动力。  相似文献   

Rates of Deglaciation during the Last Glaciation and Holocene in the Cordillera Vilcanota-Quelccaya Ice Cap Region, Southeastern Perú     

Bryan G. Mark  Geoffrey O. Seltzer  Donald T. Rodbell  Adam Y. Goodman 《Quaternary Research》2002,57(3):287

Moraine chronology is combined with digital topography to model deglacial rates of paleoglacier volumes in both the Huancané Valley on the west side of the Quelccaya Ice Cap and the Upismayo Valley on the northwest side of the Cordillera Vilcanota. The fastest rates of deglaciation (39×10⁻⁵ to 114×10⁻⁵ km³ yr⁻¹ and 112×10⁻⁵ to 247×10⁻⁵ km³ yr⁻¹ for each valley, respectively) were calculated for the most recent paleoglaciers, corresponding to the last few centuries. These results are consistent with observations in the Venezuelan Andes showing high rates of deglaciation since the Little Ice Age. These rates also fall within the range of 20th century rates of deglaciation measured on the Quelccaya Ice Cap (29×10⁻⁵ to 220×10⁻⁵ km³ yr⁻¹, Brecher and Thompson, 1993; Thompson, 2000). These results imply that rates of deglaciation may fluctuate significantly over time and that high rates of deglaciation may not be exclusive to the late 20th century. Equilibrium line altitude (ELA) depressions for the ice volumes of the last glaciation modeled here were computed as 230 m for the Quelccaya Ice Cap and 170 m for the Cordillera Vilcanota. Maximum ELA depressions are lower than previously published: <500 m for the Cordillera Vilcanota and <400 m for the Quelccaya Ice Cap. These lower values could imply a topographic control over paleoglacier extent.  相似文献   

Cretaceous length of day perturbation by mantle avalanche     

Philippe Machetel  Emilie Thomassot 《Earth and Planetary Science Letters》2002,202(2):379-386

These last 10 years, numerical models of mantle convection have emphasized the role of the 670 km endothermic phase change in generating avalanches that trigger catastrophic mass transfers between upper and lower mantle. On the other hand, scientists have emphasized the concomitance of large-scale worldwide geophysical and tectonic events, which could find their deep thermal roots in the huge mass transfers induced by the avalanches. In particular, the paleontological records show two periods of length of day (l.o.d.) shortening between 420 and 360, and 200 and 80 Myr BP. This last event is synchronous with a strong true polar wander and a global warming of the upper mantle. In order to study the potential effects of the avalanche on the main component of the Earth’s rotation, the Liouville equation has been solved and the l.o.d. evolution has been calculated from the perturbations of the inertia tensor. The results show that the inertia tensor of the Earth’s is mainly sensitive to the global transfers through the 670 km discontinuity. The l.o.d. perturbations will be synchronous with the global thermal effects of the avalanche. These theoretical results allow proposing a self-consistent physical mechanism to explain periods of the Earth’s rotation acceleration. Within this context, the l.o.d. shortening during the Cenozoic and Cretaceous brings one more clue to the possible participation of a mantle avalanche in generating the concomitant large scale events which have occurred during this very particular period of the Earth’s history.  相似文献   

Global thermal and dynamical perturbations due to Cretaceous mantle avalanche     

Philippe Machetel 《Comptes Rendus Geoscience》2003,335(1):91-97

The numerical models of mantle convection agree to depict avalanches behaviour according to the level of endothermicity of the spinel → perovskite phase change. Their potential effects on the global thermal and dynamical states of the mantle have been computed thanks to a numerical code, which takes into account both the 400-km exothermic and the 660-km endothermic phase changes. The cycle followed by the avalanches is: local layering, destabilization of the 660-km thermal layer, travelling and spreading on the core, and reappearing of the local layering. Therefore, mantle convection is characterized by quiet periods of partial layering embedded in catastrophic events. During the avalanche, the amplitude of the surface velocity is multiplied by two, which would imply an enhanced plate tectonic and ridge activities. The global thermal effects of the avalanche are compatible with a high mantle temperature and an acceleration of Earth's rotation during the Cretaceous. They also offer a coherent explanation to locate the origin of mantle plumes both within the CMB and just below the transition zone.  相似文献   

河西走廊东部强雷暴天气分析与预报          下载免费PDF全文

张星辰陈雷  把多辉刘贤 《气象科技》2003,31(5):280-283

根据1961～2000年武威站雷暴天气实况资料分析了河西走廊东部40年强雷暴天气发生的气候规律，并研究了河西走廊东部强雷暴天气发生的4种环流背景及4种主要天气条件，归纳总结出其短期预报着眼点，为雷暴天气预报业务系统的研制奠定了基础。  相似文献   

河南降水及最长连续无降水日数时空特征     

王明军侯振雨  沈素芹 《河南气象》2003,(2):18-19

利用河南省均匀分布的50个台站自建站至1997年近50年的定时降水资料，分析了河南省日小雨、日中雨、日大雨降水过程出现次数和最长连续无降水日数，结果显示，河南省日小雨、日中雨降水过程一年四季均可出现，日大而过程主要出现在3～11月份，冬季仅在豫南一些台站出现，各级降水过程出现次数季节性变化明显，冬季出现最少，夏季出现最多，其地理分布随测站纬度、拔海高度、地形地貌不同有较大差异；最长连续无降水日数也有明显的季节性变化特点，其最大值多出现在冬季，春秋次之，夏季最小，地理位置差异也较明显。  相似文献   

CHARACTERISTICS OF LARGE PULSES OF RADIATED FIELDS FROM CLOUD FLASH DISCHARGES   总被引：3，自引：0，他引：3  

祝宝友  陶善昌 《Acta Meteorologica Sinica》1997,(3)

Observations show that the sequences of microsecond-scale pulses are produced in cloud flashdischarge processes.In the present work we report on measurements of larger bipolar pulses(LBP)of the radiation fields which are classified into four types according to their waveshapes andpolarities of initial peak.Either positive or negative pulse contains two kinds of waveshapes:onewith a smooth rise and the other with 2 or 3 fast-rising pulse superimposed on the initial half cycle.The pulse waveshape characteristics in both time and frequency domains are as follows.Among2908 samples there are 45% of the positive polarity and 55% of the negative polarity.The positivepulses tend to have distinctly smaller values than negative pulses in rise time,half width and zero-crossing time of the initial peak.The peaks of positive pulse spectra tend to occur at a higherfrequency than those of negative pulses.Despite differences above,positive and negative pulseshave a similar total duration.  相似文献   

近13万年来黄土高原干湿气候的时空变迁   总被引：9，自引：1，他引：9       下载免费PDF全文

孙继敏  丁仲礼 《第四纪研究》1997,17(2):73-80

第四纪时期，黄土高原粉尘物质的搬运、沉积及其后的成土过程受控于干湿气候的变化。对黄土高原这一特定地区而言，风成沉积序列在地域上的差异主要与东亚地区的季风环流在时间和空间上的变化有关。本文的研究揭示出，近１３万年里，最为显著的成壤期有６期，与这６个成壤期对应的时段也应当是夏季风环流加强、气候温湿的时期；在空间上，全新世适宜期及末次间冰期中与深海氧同位素阶段５ａ，５ｃ，５ｅ对应的时期，夏季风足可以深入到毛乌素沙漠腹地，并具有占优势的环境效应。在阶段３的早、晚期及５ｂ时期夏季风虽然也能深入沙漠－黄土边界带，但其环境效应在黄土高原北部及毛乌素沙漠南缘已不再显著。在阶段２、阶段４及阶段３的中期夏季风已不能深入沙漠－黄土边界带。  相似文献   

地球自转研究新进展   总被引：3，自引：0，他引：3  

廖德春  郑大伟 《地球科学进展》1996,11(6):543-549

对８０年代以来关于地极移动、日长变化以及它们的地球物理激发机制的研究进展作了较为全面的评述，其中也包括了我国学者的大量研究工作。从中可以看出，现代天文测技术和多学科交叉的综合研究对天文地球动力学和地球科学进展的深远影响。  相似文献   

Study of charge structure and radiation characteristic of intracloud discharge in thunderstorms of Qinghai-Tibet Plateau     

ZHAGN Yijun  DONG Wansheng  ZHAO Yang  ZHANG Guangshu  Zhang Hongfa  CHEN Chengpin  ZHANG Tong 《中国科学D辑(英文版)》2004,47(Z1)

The comprehensive observations on lightning discharges were conducted in Naqu area of Qinghai-Tibet Plateau in summer of 2002. The electric structures of thunderstorms and the characteristics of lightning discharges at initial stage were analyzed by using the observation data. The results show that most of intracloud (IC) lightning flashes were polarities inverted in thunderstorms with tripole electric charge structure and occurred between negative charge region located in the middle of the thunderstorm and positive charge region located at the bottom of the thunderstorm. The radiation characteristics of discharge processes in cloud with longer lasting time involved in Cloud-to-Ground (CG) lightning flashes were similar to that of IC discharges.A lot of radiation pulses were produced in these discharge processes. Because the IC discharges took place at the bottom of thundercloud and were near the ground, they may produce more serious damage to equipment on the ground therefore should not be neglected in lightning protection.  相似文献