On the time-scale invariance of the eruptive activity of Vesuvius     

G. Luongo  A. Mazzarella   《Journal of Volcanology and Geothermal Research》2003,120(3-4):311-313

At Vesuvius, the intervals between final effusive eruptions since 1631 AD and those between successive plinian eruptions since 25 000 yr BP follow the same power law, when separately ranked in decreasing order. So, shifts from small to large scales are possible and this might be very helpful for the assessment of hazards of future strong volcanic activity.  相似文献   

Astronomical time-scale for physical property records from Quaternary sediments of the northern North Atlantic     

Jürgen Mienert  Jian Chi 《International Journal of Earth Sciences》1995,84(1):67-88

Deep sea sediment cores taken between 50° and 75°N in the North Atlantic, in water depths varying between 1340 and 3850 m, were examined to provide an astronomically calibrated late Quaternary time-scale based on physical property records. Magnetic susceptibility and gamma ray attenuation porosity evaluator (GRAPE) density changes of these cores revealed significant responses to orbital forcing in the eccentricity (100 kyr), obliquity (41 kyr) and precessional (23, 19 kyr) bands. At 75°N (Greenland Sea), a response to obliquity forcing was weak despite the fact that it should become more pronounced in sediments at high latitudes. Application of bandpass filtering at the obliquity period (41 kyr), however, showed that variance at this period did exist in the magnetic susceptibility record, but at a very low power. At 50°N stacked curves of magnetic susceptibility correlated strongly with the SPECMAP curve for the past 500 ka. Since about 65 ka, dropstone layers are recorded in both magnetic susceptibility and GRAPE data of Rockall Plateau sediments. Although Rockall Plateau sediments show peaks in physical properties that correlate with Heinrich events (H₁, H₂, H₄, H₅, H₆), such a relationship was not readily observed in Norwegian-Greenland Sea records. Heinrich events at Rockall Plateau sites indicate a northward flow of icebergs in the eastern North Atlantic. This flow pattern and the presence of Heinrich events during the past 65 ka raise the questions of whether similar events occurred before this time period, and to what kind of ice sheet dynamics and climatic-oceanographic conditions favoured major iceberg surges from the Laurentide ice sheet to the North Atlantic at 50°N.  相似文献   

Luni-solar 18.6-year signal in tree-rings from Argentina and Chile     

Robert G. Cùrrie 《Pure and Applied Geophysics》1991,137(3):281-300

Spectrum analysis of 32 tree-ring chronologies from Argentina and Chile yields evidence for two peaks with periods 19.2±1.6 years (30 out of 32 records) and 10.5±0.4 years in 22 instances. Tests by thet-statistic show that the long-period peak is significant at a confidence level of 99%. This signal is identified as the luni-solar 18.6-year M _n term reported earlier byCurrie (1983) in two treering chronologies from the same region, and later in tree-rings from North America, Tasmania, New Zealand, and South Africa (Currie, 1991a-c). Amplitude and phase of the M _n signal are nonstationary with respect to both time and geography. In particular, abrupt 180° phase changes in wave polarity are often observed.  相似文献   

基于等级钟理论的中国城市规模等级体系演化特征   总被引：5，自引：0，他引：5  

刘妙龙  陈雨  陈鹏  陈捷 《地理学报》2008,63(12):1235-1245

首次引入国际著名城市地理学家M.Batty 提出的“城市规模等级钟”、“等级距离钟” 和“半生命周期” 理论; 利用地级以上城市的人口-等级数据, 测算了表征中国城市规模等 级演化特点的“等级钟”、“等级距离钟” 和“半生命周期”, 探讨了演化过程与机制; 利用 历史人口数据, 研究了若干历史城市近2000 年间的“等级钟” 演化特征。等级钟研究表明, 中国特大城市的规模等级钟变化较小, 城市位序稳定; 在区域空间差异上, 东部沿海城市等 级钟变化明显, 位序上升迅速; 东北地区城市等级钟呈现较大变化, 但演化方向与东部沿海 城市相反, 城市位序逐渐下降; 西部和内陆城市等级钟变化缓慢, 位序难以进入顶级序列之 中。等级距离钟表明, 中国高位序城市等级距离变化较小, 低位序和新设立城市的等级距离 变化明显, 整个城市系统的变化较为平缓, 仅在1980-1985 年间和2000-2005 年间出现较大变化, 体现了中国在改革开放初期与21 世纪开始的二次较为迅速的城市化发展历程。半生命周 期研究表明, 中国城市体系在生命周期现象不明显的总体背景下, 以20 世纪80 年代为时间 界标, 百位城市的前、后半生命周期仍然显现有较为明显的时间尺度差异, 自该时间界标以后, 新兴城市替代传统城市的速度开始加快。中国历史城市“等级钟” 表明, 城市位序等级 的变化是多种动因的叠加, 以政治职能为主的城市位序与其政治地位密切相关; 沿海、沿江 城市的位序则更多地与地理区位条件和经济政策相关联。  相似文献   

中国沙漠科学的五十年   总被引：40，自引：20，他引：20  

王涛  赵哈林 《中国沙漠》2005,25(2):145-165

50多年来,在几代沙漠科技人员的不懈努力下,中国的沙漠科学从无到有,在从填补沙漠研究空白并取得长足进展的同时,沙漠化研究又以其创新性和系统性的理论进展,经济、社会和环境效益的实践成果,极大地充实了我国的沙漠科学,为我国北方地区国民经济建设和生态环境保护做出了突出的贡献,取得了包括国家科技进步特等奖在内的一大批科研成果和上百亿元的直接经济效益。过去20 a来,北方约有 10%的沙漠化土地得到治理,12%的沙漠化土地有所改善,局部地区出现"人进沙退"的新局面。已形成了以中国科学院和国家林业局等有关研究所为主体的国家级沙漠和沙漠化研究机构,汇集了一批优秀的沙漠和沙漠化科学家,创建了我国比较完整的沙漠和沙漠化科学及其研究体系,在风沙物理与沙漠环境、沙漠形成演变与全球变化、沙漠化过程及其防治、沙区资源环境与可持续发展、沙漠化遥感与信息系统综合研究等方面取得了重大进展,积累了丰富的研究资料和数据。在全国主要沙漠和沙漠化地区设有一批长期野外试验站(点),已为国家在有关沙漠开发利用和沙漠化防治方面的决策提供了大量的科研成果和理论依据。我国沙漠科学研究和实践所取得的辉煌成就,得到了政府、地方民众、科学界和国际社会的普遍认可。  相似文献   

Wind-driven wave heights in the German Bight   总被引：1，自引：0，他引：1  

Stefan Emeis  Matthias Türk 《Ocean Dynamics》2009,59(3):463-475

Wind speed, friction velocity and significant wave height data from the FINO1 platform in the southern German Bight 45 km off the coast for the years 2004 to 2006 have been evaluated and related to each other. The data show a clear dependence of the hourly mean wave height to the hourly mean friction velocity and wind speed. Wave heights increase with decreasing stratification and increasing fetch. Synoptic weather patterns for the highest wave heights in the southern German Bight are determined. The analysis is made separately for four wind direction sectors. The two strongest storms in the evaluated period, “Britta” and “Erwin”, are analysed in more detail. Finally, the 50-year extreme significant wave height has been estimated to be about 11 m most probably coming from northerly directions.  相似文献   

Prediction of china’s submerged coastal areas by sea level rise due to climate change   总被引：2，自引：0，他引：2  

ZUO Juncheng  YANG Yiqiu  ZHANG Jianli  CHEN Meixiang  XU Qing 《中国海洋大学学报(英文版)》2013,12(3):327-334

Based on the simulation with the Ocean-Atmosphere Coupled Model CCSM and Ocean Model POP under the greenhouse gas emission scenario of the IPCC SRES A2 (IPCC, 2001), and on the earth crust subsidence and glacier melting data, the relative sea level change is obtained along the coast of China in the 21st century. Using the SRTM elevation data the submergence of coastal low land is calculated under the extreme water level with a 100-year return period. The total flooding areas are 98.3×10³ and 104.9×10³ km² for 2050 and 2080, respectively. For the three regions most vulnerable to extreme sea level rise, i.e., the coast of Bohai Bay, the Yangtze River Delta together with neighboring Jiangsu Province and northern Zhejiang Province, and the Pearl River Delta, the flooded areas are 5.0×10³, 64.1×10³ and 15.3×10³ km² in 2050 and 5.2×10³, 67.8×10³ and 17.2×10³ km² in 2080, respectively.  相似文献   

旬阳东段汉江全新世古洪水研究     

王龙升  黄春长  庞奖励  查小春  周亚利  李晓刚  张玉柱 《地理科学进展》2012,31(9):1141-1148

通过对汉江上游河谷的考察, 在旬阳县东段构元－棕溪乡河段发现的典型的全新世古洪水滞流沉积剖面, 进行了古洪水沉积学和水文学研究。在野外考察的基础上, 对于采集的全新世地层剖面序列样品, 进行粒度成分和磁化率等分析测试, 从沉积角度揭示了这些沉积层是古洪水在高水位滞流环境中悬移质泥沙的沉积物。通过地层对比分析确定由其记录的古洪水事件分别发生全新世早期9000~8500 a B.P.和全新世晚期3200~2800 aB.P.。利用古水文学原理恢复其洪峰水位, 计算出古洪水洪峰流量介于45630~50220 m³/s 之间。结合现代洪水洪痕洪峰计算、洪峰流量与流域面积关系分析多种方法, 对古洪水洪峰流量计算结果进行了验证, 从而建立了更加可靠的万年尺度洪峰流量与频率关系。本文的研究成果, 对汉江上游水资源开发、防洪减灾、水土保持和深入理解汉江上游水文过程对全球变化的响应规律具有重要的科学意义。  相似文献   

郑州近54年降水变化的多时间尺度分析   总被引：5，自引：0，他引：5  

刘忠阳  王勇  丁园圆  杨海鹰  杜子璇 《气象科技》2005,(Z1)

利用Morlet小波分析方法,对1951~2004年郑州市年降水距平时间序列的小波变化特征进行分析,揭示降水变化的多时间尺度结构,分析其中存在的主要周期振荡和突变点,并与功率谱分析结果进行比较。结果表明:郑州市年降水存在多时间尺度的周期变化特征,郑州市年平均降水存在3 a、准5 a、准9 a和准21 a的主周期。郑州市降水变化存在着明显的多时间尺度,即年代际尺度和年际尺度的周期性变化。郑州市降水变化还显示出自己的突变点分布及其位相结构。在降水量总趋势下降的前提下,2004年后的一段时间还将处在一个偏多期。  相似文献   

岩浆成矿系统的尺度效应   总被引：2，自引：0，他引：2  

罗照华  苏尚国  刘翠 《地球科学与环境学报》2014,(1):1-9

小岩体成大矿理论强调了岩浆侵入体的几何尺度与内生金属成矿作用的有机联系,但这种联系的实质尚理解甚少。简要分析了岩浆成矿系统的基本问题,聚焦于侵入体几何尺度与几种关键控矿因素的内在联系。利用前人提出的固相线前锋迁移距离与冷却时间之间的函数关系估算了岩浆侵入体固结的时间尺度,发现小岩体的存活时间尺度与超大型矿床的形成时间尺度一致。基于斯托克定律的估算,含有暗色微粒包体的小岩体以岩浆快速上升为特征,符合流体中成矿金属溶解度与压力(P)、温度(T)正相关的实验结果。分析了岩浆产量与源区减压速率和所产生岩浆中挥发分含量之间的关系,提出大规模岩浆活动之后岩浆产量必然逐渐减少,因而流体-熔体比值逐渐增加。据此认为,超大型矿床可形成于紧接着大规模岩浆活动之后,并以长英质岩浆成矿系统为例将其称为岩基后成矿作用。因此,岩浆成矿系统的尺度效应是一种重要的地质效应,尺度效应分析支持小岩体成大矿理论。  相似文献