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681.
An ensemble of stochastic daily rainfall projections has been generated for 30 stations across south‐eastern Australia using the downscaling nonhomogeneous hidden Markov model, which was driven by atmospheric predictors from four climate models for three IPCC emissions scenarios (A1B, A2, and B1) and for two periods (2046–2065 and 2081–2100). The results indicate that the annual rainfall is projected to decrease for both periods for all scenarios and climate models, with the exception of a few scenarios of no statistically significant changes. However, there is a seasonal difference: two downscaled GCMs consistently project a decline of summer rainfall, and two an increase. In contrast, all four downscaled GCMs show a decrease of winter rainfall. Because winter rainfall accounts for two‐thirds of the annual rainfall and produces the majority of streamflow for this region, this decrease in winter rainfall would cause additional water availability concerns in the southern Murray–Darling basin, given that water shortage is already a critical problem in the region. In addition, the annual maximum daily rainfall is projected to intensify in the future, particularly by the end of the 21st century; the maximum length of consecutive dry days is projected to increase, and correspondingly, the maximum length of consecutive wet days is projected to decrease. These changes in daily sequencing, combined with fewer events of reduced amount, could lead to drier catchment soil profiles and further reduce runoff potential and, hence, also have streamflow and water availability implications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
682.
I. Lerche 《Mathematical Geology》1988,20(2):73-96
Using the logic for quantitative inversion of present-day downhole thermal indicators, the inversion procedure can be used to determine unknown, or poorly known, chemical and physical parameters as well as other geological quantities of interest which impact on burial history and thermal history of an evolving sedimentary basin. Some such quantities are: amount of erosion and timing of unconformities, paleo-overpressuring, stratigraphic age, timing of igneous intrusion and insertion temperature, overthrust timing and frictional heating, fault and slump timing, effects due to emplacement of a radiocative layer, and salt emplacement and dissolution timing. Combining a priori unknown values of these chemical/physical and geological parameters with unknown (a priori) paleoheat flux variations, a theoretical scheme, called thermal indicator tomography, is developed for the systematic determination of all parameters at the same time and on the same footing. Case histories will be discussed in subsequent papers in this series. 相似文献
683.
The Hikurangi Margin is a region of oblique subduction with northwest-dipping intermediate depth seismicity extending southwest from the Kermadec system to about 42°S. The current episode of subduction is at least 16–20 Ma old. The plate convergence rate varies along the margin from about 60 mm/a at the south end of the Kermadec Trench to about 45 mm/a at 42°S. The age of the Pacific lithosphere adjacent to the Hikurangi Trench is not known.The margin divides at about latitude 39°S into two quite dissimilar parts. The northern part has experienced andesitic volcanism for about 18 Ma, and back-arc extension in the last 4 Ma that has produced a back-arc basin onshore with high heaflow, thin crust and low upper-mantle seismic velocities. The extension appears to have arisen from a seawards migration of the Hikurangi Trench north of 39°S. Here the plate interface is thought to be currently uncoupled, as geodetic data indicate extension of the fore-arc basin, and historic earthquakes have not exceededM
s=7.South of 39°S there is no volcanism and a back-arc basin has been produced by downward flexure of the lithosphere due to strong coupling with the subducting plate. Heatflow in the basin is normal. Evidence for strong coupling comes from historic earthquakes of up to aboutM
s=8 and high rates of uplift on the southeast coast of the North Island.The reason for this division of the margin is not known but may be related to an inferred increase, from northeast to southwest, in the buoyancy of the Pacific lithosphere. 相似文献
684.
一、前言 中纬度地区电离层Es的成因与影响因素是一复杂的问题。远东地区Es既多又强,其它电离层现象也有一些特色,本文在文献[9]的基础上,从分析原始频高图入手,对远东地区夜间f0Es剧增与地磁K指数的关系作了统计研究,发现两者之间关系甚为密切,即地磁K指数的突然变化伴随着夜间Es层临界频率f0Es的剧烈增加。 相似文献
685.
686.
本文研究了我国大陆地区五级以上地震的时间间隔分布情况,发现我国大陆M_S≥5.0地震的时间间隔ΔT与其频次N_(ΔT)之间存在以下关系式:lgN_(ΔT)=2.14-0.15·ΔT本文还讨论了我国大陆出现长期无五级以上地震后,是否将有七级地震的问题。 相似文献
687.
688.
The determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances. The technique is based on two main principles. Firstly, 234U is more mobile than 238U, especially during the early stages of weathering. Secondly, uranium is far more mobile than either thorium or protactinium. Consequently, teaching during weathering results in the loss of the uranium found in the fresh rock, leaving the two immobile daughters behind. The ratio of uranium carried by sediment to that dissolved, US/UW can, therefore, be determined from river water and sediment isotopic activity ratios. Fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment, from which a sediment yield can be inferred. The Witham catchment in Lincolnshire has been used to test the proposed method. A US/UW ratio of between 5 and 7 is determined and a sediment yield of 2.51 ± 2.12 tonnes yr?1 km?2 is proposed. Although some problems concerning environmental chemistry have arisen, the validity of the approach is confirmed by the close correspondence between the results obtained and those inferred by earlier workers using more conventional methods. 相似文献
689.
辽宁省金矿集中区及其与构造样式的关系 总被引:1,自引:0,他引:1
本文将辽宁省金矿划分四种类型,十个主要金矿集中区。这些集中区均受华北地台东西向基底构造活动带及中生代太平洋板块俯冲影响、所产生的北西向构造挤压带和北东向构造—岩浆岩带的复合作用控制。它们分别处于太不洋成矿带的内带(辽东)和外带(辽西)。并以郯庐断裂为轴线,构成了两大“U”字形,类似共轭曲线展布的构造样式。根据深部地球物理资料,综合分析了控制金矿集中区构造样式的形成机制。区内脉状金矿大都分布在深断裂(深度大于五公里断裂)带附近。 相似文献
690.
The C and H isotopic compositions of the methane in more than 160 gas samples from 10 basins in China are presented in this paper.The natural gases are classified as four types: biogenic gas ,bio-thermocatalytic transitional gas, gas associated with condensate oil ,and coal-type gas. The isotopic compositions of these gases closely related to the depositional basins, the types of organic matter,the stages of thermal evolution and the genetic characteristics of different gas reservoirs.Studies of the C and H isotopic compositions of terrigenous natural gases will provide valua-ble information on the prospecting and development of natural gases of different genetic types. 相似文献