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421.
422.
423.
Influence of the Atlantic Multidecadal Oscillation on the winter climate of East China 总被引:11,自引:0,他引:11
The Atlantic Multidecadal Oscillation (AMO), the multidecadal variation of North Atlantic sea surface temperature (SST), exhibits an oscillation with a period of 65-80 years and an amplitude of 0.4℃. Observational composite analyses reveal that the warm phase AMO is linked to warmer winters in East China, with enhanced precipitation in the north of this region and reduced precipitation in the south, on multidecadal time scales. The pattern is reversed during the cold phase AMO. Whether the AMO acts as a forcing of the multidecadal winter climate of East China is explored by investigating the atmospheric response to warm AMO SST anomalies in a large ensemble of atmospheric general circulation model (AGCM) experiments. The results from three AGCMs are consistent and suggest that the AMO warmth favors warmer winters in East China. This influence is realized through inducing negative surface air pressure anomalies in the hemispheric-wide domain extending from the midlatitude North Atlantic to midlatitude Eurasia. These negative surface anomalies favor the weakening of the Mongolian Cold High, and thus induce a weaker East Asian Winter Monsoon. 相似文献
424.
A reasonable warmer winter index (IWWI) in the framework of the three equiprobability categories (i.e. warmer, normal and colder categories) is proposed based on the winter temperature data observed at 565 stations in China during 1956-2005, where IWWI is defined as the ratio of the station number of warmer category over the total number of stations. The results suggest that the trend of IWWI was consistent with that of the winter temperature on decadal time scale, and their rates of change were 10%/10 a and 0.4 ℃/10 a, respectively. It is found that only 13 warmer winter events in total were detected by IWWI over the past 50 years, and 85% of them occurred after 1986. 相似文献
425.
Normalized Difference Vegetation Index (NDVI) data were used to investigate vegetation changes after Hurricane Katrina (2005)
for the Weeks Bay Reserve and surrounding area of coastal AL. Landsat 5 satellite images were acquired before landfall (March
24, 2005), after landfall (September 16, 2005), and 8 months after landfall (April 28, 2006). The March 2005 to September
2005 image comparison showed that average NDVI values decreased by 49% after landfall. Continuing into the next year, average
NDVI values were −44% lower in April 2006 than they were in March 2005. Among habitat types, the estuarine emergent wetland
experienced the largest average NDVI value decrease (−64%). The estuarine emergent wetland NDVI values continued to decrease
by −27% from September 2005 to April 2006, whereas other habitats increased in NDVI. This continued suppression of NDVI values
was attributed to increased salinity from the storm surge and to regional drought conditions that occurred after landfall.
These results provide insight into the sensitivity of coastal vegetation from the interactions of both tropical cyclones and
long-term environmental conditions. 相似文献
426.
427.
青藏高原东北缘寺口子盆地新生代沉积演化及其构造意义 总被引:2,自引:0,他引:2
宁夏固原寺口子盆地发育巨厚的新生代地层,这些地层记录了青藏高原东北部的沉积演化特征和构造演变历史。根据剖面沉积物粒度特征、沉积结构和构造、沉积层序,识别出20种岩相、5种沉积相类型。结合前人对寺口子剖面的古地磁测年,分析研究盆地的沉积演化特征以及对构造的响应表明:20.1 Ma盆地以缓慢的坳陷沉降开始演化,直至1.2 Ma遭受破坏。在此期间青藏高原东北部经历了6.4 Ma、4.6 Ma和1.2 Ma这3次明显的构造挤压隆升运动,其中约6.4 Ma的构造运动是青藏高原向东北部扩展首次影响到海原—六盘山断裂以东地区。从盆地的形成和沉积演化过程来看,马东山山前断裂的逆冲推覆,导致了寺口子盆地的强烈变形和构造降升,并且最终成为青藏高原的最新组成部分。 相似文献
428.
探讨构造、气候与砾岩的关系对于研究青藏高原隆升的时间和方式具有重要意义。裂变径迹热年代学表明积石山地区于8MaB.P.开始构造变形,与碎屑颗粒裂变径迹结果和生长地层结果一致,而明显早于积石砾岩出现的时间(3.6MaB.P.)。通过区分岩体隆升与地面隆升之间的差别,文章提出一种新的模型,以解释隆升、气候和砾岩之间的关系。积石山岩体于8MaB.P.开始隆升,隆升初期,尽管岩体隆升1500~2000m,但是由于积石山上覆的新生代地层易于剥蚀,在花岗岩基底被剥露到地表之前,地表只有少量隆升或没有隆升。随着沉积地层被剥蚀殆尽,基岩暴露于地表,地面隆升速率加快。约3.6MaB.P.,积石山隆升约200~900m,造成了地形雨和发源于积石山的横向河流的出现,这些横向河流把积石山的花岗岩搬运到盆地中沉积下来,形成积石砾岩。 相似文献
429.
I. González M. M. Jordán T. Sanfeliu M. Quiroz C. de la Fuente 《Environmental Geology》2007,52(7):1243-1251
In southern Chile, with a mild and rainy climate, high levels of heavy metals have been detected in many gold placer deposits.
Many of the contaminants pose risks to human life, and consequently damage the trofic chain in this environment. The study
zones selected correspond to the handicraft gold-bearing sands of Rio Gato (Los Muermos), Carelmapu and Cucao. These are all
located in the X Region of “Los Lagos” in Chile. The type of methodology used in the characterization of the associated mineralization
consists of testing each representative sample with a grain size distribution, statistical parameter analysis and a mineralogical
analysis, using a binocular magnifying glass, a petrographic microscope, XRD and SEM/EDX. The chemical composition was defined
by means of X ray fluorescence and micro-chemical analysis. The results of the study about sediments in southern Chile are
presented. The major concentrations of heavy minerals are generally located in areas of dynamic river energy. In the samples,
more than 70% of the heavy minerals were distributed among grain sizes corresponding to thin sand with good grain selection
(meshes of 0.25–0.06 mm). The main mineral phases present in the analysed samples were gold, zircon, olivine, ilmenite, hornblende,
hypersthene, hematite, garnet, chromite, chlorite, augite, amphibolitic-epidote, etc. The main heavy metals found as a result
of the study were mercury, lead, cadmium, chrome, tellurium, indium, zinc, cobalt, copper, platinum, gold, etc., and as well
some less common elements like cerium, praseodymium, gadolinium, neodymium, samarium and lanthanum. This research work is
only a starting point for carrying out a risk probability mapping of heavy metals and the mineralogy of the Cucao, Carelmapu
and Rio Gato gold-bearing sands. 相似文献
430.
新矿物——张衡矿 总被引:6,自引:2,他引:6
张衡矿是在安徽毫县陨石中发现的一种天然矿物。其共生矿物有橄榄石、单斜辉石、斜方辉石、斜长石、正长石、白磷钙矿、石英、黑云母、白云石、方解石、刚玉、陨硫铁、铁纹石、镍纹石、铬铁矿、钛铁矿、镁铁尖晶石、镍黄铁矿、石墨、方铁矿、自然铜、磁铁矿等。矿物为金黄色,条痕铜黄色。不透明,具金属光泽。晶体为粒状、不规则粒状、片板状、树枝状,粒度为0.13×0.15-0.1×0.35mm~2。H_?=145-150kg/mm~2。无理解。密度(计算值)=8.32g/cm~3。反光下为亮黄色,均质。电子探针分析结果;Cu52.77,Zn46.78,Fe0.12,Al0.05,Cr0.25,Ni0.01,总和99.98wt%。理想化学式为CuZn。经X射线粉晶分析确定为等轴晶系,体心格子,无序结构,空间群为Im3m,a=2.952(2)A。晶胞体积V=25.72A~3,Z=1。 相似文献