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101.
利用1981~2002年全国土壤湿度资料,利用相关分析发现东亚夏季风和河套地区及西南地区春季土壤湿度之间存在较大的正相关,利用这两个区域的春季土壤湿度定义了一个标准化春季土壤湿度指数(SMI),结果发现:(1)SMI和东亚夏季风的强弱相关较好。高指数年东亚季风区低空西南夏季风气流和高层东风气流明显偏强,表明这一年夏季风偏强,低指数年则相反;(2)强SMI年,西太平洋副热带高压位置偏北,强度偏弱,西风扰动带偏北,有利于夏季风北推,不利于北方冷空气南下与之交汇,使得锋区偏北,位于华北、东北地区。弱SMI年则反之;(3)SMI能够较好地反映东部地区夏季降水,在强SMI年,长江流域降水明显偏少,而华北和河套地区的降水明显增多,而弱SMI年正好相反,这与东亚夏季风降水的环流形势也较为吻合(;4)SMI指数存在明显的4~6年和准2年的周期振荡,但其振幅和周期又有明显的周期变化。在对东亚夏季风强度的预报能力上,负的SMI对弱东亚夏季风的预报能力要强于正SMI对强东亚夏季风的预报能力。 相似文献
102.
103.
The Apollo-12 ALSEP solar wind spectrometer obtained data from the lunar surface starting November 20, 1969. To a first approximation, the general features of the positive ion flux depend only on the instrument's orientation and location in space relative to the Sun-Earth system. However, there are some detectable effects of the interaction of the solar wind with the local magnetic field and surface, including the deceleration of incident positive ions and the enhancement of fluctuations in the plasma. The expected asymmetry of sunset and sunrise times due to the motion of the Moon about the Sun is not observed. On one occasion, the solar wind was incident on the ALSEP site as early as 36 hr (18°) before sunrise. 相似文献
104.
Hafnium isotope and incompatible trace element data are presentedfor a suite of mid-ocean ridge basalts (MORB) from 13 to 47°Eon the Southwest Indian Ridge (SWIR), one of the slowest spreadingand most isotopically heterogeneous mid-ocean ridges. Variationsin NdHf isotope compositions and Lu/Hf ratios clearlydistinguish an AtlanticPacific-type MORB source, presentwest of 26°E, characterized by relatively low Hf valuesfor a given Nd relative to the regression line through all NdHfisotope data for oceanic basalts (termed the NdHfmantle array line; the deviation from this line is termedHf) and low Lu/Hf ratios, from an Indian Ocean-type MORB signature,present east of 32°E, characterized by relatively high Hfvalues and Lu/Hf ratios. Additionally, two localized, isotopicallyanomalous areas, at 1315°E and 3941°E,are characterized by distinctly low negative and high positiveHf values, respectively. The low Hf MORB from 13 to 15°Eappear to reflect contamination by HIMU-type mantle from thenearby Bouvet mantle plume, whereas the trace element and isotopiccompositions of MORB from 39 to 41°E are most consistentwith contamination by metasomatized Archean continental lithosphericmantle. Relatively small source-melt fractionation of Lu/Hfrelative to Sm/Nd, compared with MORB from faster-spreadingridges, argues against a significant role for garnet pyroxenitein the generation of most central SWIR MORB. Correlations betweenHf and Sr and Pb isotopic and trace element ratios clearly delineatea high-Hf Indian Ocean mantle component that canexplain the isotope composition of most Indian Ocean MORB asmixtures between this component and a heterogeneous AtlanticPacific-typeMORB source. The Hf, Nd and Sr isotope compositions of IndianOcean MORB appear to be most consistent with the hypothesisthat this component represents fragments of subduction-modifiedlithospheric mantle beneath Proterozoic orogenic belts thatfoundered into the nascent Indian Ocean upper mantle duringthe Mesozoic breakup of Gondwana. KEY WORDS: mid-ocean ridge basalt; isotopes; incompatible elements; Indian Ocean 相似文献
105.
基于表格的通用管理信息系统的设计 总被引:2,自引:2,他引:0
作者提出了一种表格式通用管理信息系统的设计方案,介绍了系统的设计思想、主要工作流程、系统各组件的功能、作用及相互关系等还详细介绍了系统主要数据库的设计。 相似文献
106.
On Hatteras Island, North Carolina, USA, complex stratigraphy results from surficial sediments being superimposed on an inherited
Pleistocene platform. Numerical simulations used to simulate water-table profiles on the island illustrate the influence that
the complex stratigraphy has on water-table elevations. Field data consist of water-table profiles collected from a cross-island
transect of wells. These profiles show unusually high water-table elevations in the south-central portion of Hatteras Island.
Geophysical data are used to constrain the subsurface stratigraphy. Simple analytical solutions to the groundwater flow equation
using laterally varying recharge rates cannot match mean water-table profiles. More complex numerical simulations, which do
match the profiles, indicate that the elevated water levels result from a low-permeability unit that extends several kilometers
along the longitudinal axis of the island. Island geomorphology and ground-penetrating radar (GPR) data suggest that this
unit is a former interdunal wetland that has been buried by a series of parabolic dunes.
Received, September 1999 / Revised, March 2000 / Accepted, March 2000 相似文献
107.
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109.
J.F. Perez-Quezada C.A. DelpianoK.A. Snyder D.A. JohnsonN. Franck 《Journal of Arid Environments》2011,75(1):29-37
The pattern of carbon (C) allocation among the different pools is an important ecosystem structural feature, which can be modified as a result of changes in environmental conditions that can occur gradually (e.g., climatic change) or abruptly (e.g., management practices). This study quantified the C pools of plant biomass, litter and soil in an arid shrubland in Chile, comparing the natural condition (moderately disturbed by grazing) vs. the afforested condition (two-year-old plantation with Acacia saligna (Labill.) H.L. Wendl.), each represented by a 60 ha plot. To estimate plant biomass, allometric functions were constructed for the four dominant woody species, based on the volume according to their shape, which showed high correlation (R2 > 0.73). The soil was the largest C pool in both natural and afforested conditions (89% and 94%, respectively) and was significantly lower in the afforested than natural condition at all five soil depths. The natural condition had in total 36.5 ton (t) C ha−1 compared to 21.1 t C ha−1 in the afforested condition, mainly due to C loss during soil preparation, prior to plantation of A. saligna. These measurements serve as an important baseline to assess long-term effects of afforestation on ecosystem C pools. 相似文献
110.
硒圣河是湄公河的主要分支之一,其集水区地形条件和水资源量均对水电开发十分有利。此外,无论从物种多样性还是生物量来看,硒圣河水生生物资源非常丰富。鱼类是当地人们的重要食物来源,粗略估计鱼类物种数量可能在200-300种之间,目前具有详细记录的鱼类大约为120种。截至目前,从越南境内硒圣河上游至越-柬边界总共开发了6个水电项目,兴建了一座4A级硒圣调蓄水库。流经柬埔寨的硒圣河部分,依据发展规划将兴建3座水电站,即硒圣5号电站(硒圣1号电站以下)、硒圣3号电站、硒圣2号电站。硒圣河水电项目对区域(越南和柬埔寨)社会经济的影响体现在:为地处偏远和困难的集水区创造了新的能源资源,改善了交通系统和农村地区的生活条件。与此同时,这些水电项目也对该区域自然环境产生了重大影响。例如,改变了下游流动机理变化,导致下游河道淤积,对沿河生态系统也产生了一定影响。 相似文献