华山松树木年轮对气候响应的模拟分析   总被引：19，自引：1，他引：19       下载免费PDF全文

尹训钢  吴祥定 《应用气象学报》1995,6(3):257-264

采用树木年轮生长模型，从细胞尺度对华山松在不同时期的树木生长状况，包括早材和晚材的细胞大小等年轮结构变化进行了模拟。所建立的细胞大小年表对气候的响应函数结果，揭示出华山松的生长主要受生长季中4～7月份以及滞后一年降水的影响，而温度只是在生长季节开始的4月份起限制作用。利用气候资料对华山松的细胞大小及变化趋势的模拟结果表明，它与实测值十分接近。  相似文献   

Evidence for volatile-influenced differentiation in a layered alkali basalt flow, Penghu Islands, Taiwan     

John D. Greenough  Chi-Yu Lee  Brian J. Fryer 《Bulletin of Volcanology》1999,60(6):412-424

An approximately 20-m-thick alkali basalt flow on the Penghu Islands contains ∼20 cm thick, horizontally continuous (>50 m), vesicular layers separated by ∼1.5 m of massive basalt in its upper 8.5 m. The three layers contain ocelli-like "vesicles" filled with nepheline and igneous carbonate. They are coarse grained and enriched in incompatible elements relative to the massive basalt with which they form sharp contacts. These vesicular layers (segregation veins) formed when residual liquid in the underlying crystal mush was forced (gas filter pressing) or siphoned into three thermally induced horizontal cracks that opened successively in the advancing crystal mush of the flow's upper crust. Most vesicular layer trace elements can be modelled by residual melt extraction after 25–40% fractional crystallization of massive basalt underlying each layer. Sulphur, Cl, As, Zn, Pb, K, Na, Rb, and Sr show large concentration changes between the top, middle, and bottom layers, with each vesicular and underlying massive basalt forming a chemically distinct "pair." The large changes between layers are difficult to account for by crystal fractionation alone, because other incompatible elements (e.g., La, Sm, Yb, Zr, Nb) and the major elements change little. The association of these elements (S, Cl, etc.) with "fluids" in various geologic environments suggests that volatiles influenced differentiation, perhaps by moving alkali, alkaline earth, and chalcophile elements as magma-dissolved volatile complexes. Volatiles may have also led to large grain sizes in the segregation veins by lowering melt viscosities and raising diffusion rates. The chemical variability between layers indicates that a convection and concentration mechanism acted within the flow. The specific process cannot be determined, but different rates of vesicle plume rise (through the flow) and/or accumulation in the upper crust's crystal mush might account for the chemical pairing and extreme variations in Cl, S, As, and C. This study emphasizes the importance of sampling vesicular rocks in flows. It also suggests that volatiles play important physical and chemical roles in rapidly differentiating mafic magmas in processes decoupled from crystal fractionation. Received: 11 November 1996 / Accepted: 20 September 1998  相似文献   

长江三角洲地区地磁短周期变化异常的描述及解释          下载免费PDF全文

顾左文  范国华 《地球物理学报》1994,37(1):66-77

在长江三角洲地区进行了地磁短周期变化的观测，对资料的分析表明，该区域地磁短周期变化存在一非对称异常．其负异常较大，中心位于无锡、常熟一带；其正异常较小，中心位于海安与大丰之间．异常出现的周期为１００-３６００ｓ，并在１２０ｓ处取极大值．二维模型拟合表明，在该地区存在一由北向南上升的地下高导层．该高导层在溧阳、无锡、余山一线消失．这恰是溧阳、崇明大断裂之所在．该地区地表还存在有厚度为３００ｍ的高导覆盖层．  相似文献   

武威盆地泉群流量模拟及预测的一种方法     

王根绪  张惠昌 《甘肃地质》1993,2(1):95-101

本文根据系统理论及灰色预测理论,建立了武威盆地泉群流量模拟及预测模型,依据该模型可通过下游香家湾站河水流量的观测值,推断出整个盆地泉群流量,经过1978—1983 5年的资料验证,结果准确可靠。  相似文献   

Crystal morphology and surface structures of orthorhombic MgSiO3 perovskite     

M. Alfredsson  J. P. Brodholt  D. P. Dobson  A. R. Oganov  C. R. A. Catlow  S. C. Parker  G. D. Price 《Physics and Chemistry of Minerals》2005,31(10):671-682

Orthorhombic MgSiO₃ perovskite is thought to be the most abundant mineral in the mantle of the Earth. Its bulk properties have been widely studied, but many geophysical and rheological processes are also likely to depend upon its surface and grain boundary properties. As a first step towards modelling these geophysical properties, we present here an investigation of the structures and energetics of the surfaces of MgSiO₃-perovskite, employing both shell-model atomistic effective-potential simulations, and density-functional-theory (DFT) calculations. Our shell-model calculations predict the {001} surfaces to be the energetically most stable surfaces: the calculated value of the surface energy being 2.2 J/m² for the MgO-terminated surface, which is favoured over the SiO₂-terminated surface (2.7 J/m²). Also for the polar surfaces {111}, {101} and {011} the MgO-terminated surfaces are energetically more stable than the Si-terminated surfaces. In addition we report the predicted morphology of the MgSiO₃ perovskite structure, which is dominated by the energetically most stable {001} and {110} surfaces, and which appears to agree well with the shape of grown single crystals.  相似文献   

Assessing agreement of measurements and predictions in geomorphology     

Nicholas J. Cox   《Geomorphology》2006,76(3-4):332-346

Commonly in geomorphology measurements by different methods are compared to see how far they agree (i.e. are equal), as are predictions from models and corresponding observations. Such assessment usually employs scatter plots, correlation and possibly regression. More appropriate and more effective methods include plotting differences versus means and summary by concordance correlation and other measures of agreement. These methods, some new to geomorphology, are explained and discussed with a variety of examples using fluvial, hillslope, glacial and coastal data.  相似文献   

Effects of trench-zone scattering on receiver functions over a subduction zone: A 3-D finite-difference modelling study     

Igor B. Morozov  Haishan Zheng 《Tectonophysics》2006,420(1-2):317

As Morozov [Morozov, I. B. (2004). Crustal scattering and some artefacts in receiver function images. Bull. Seismol. Soc. Am., 94 (4), 1492–1499.] suggested, for a teleseismic array targeting subducting crust in a zone of active subduction, scattering from the strong horizontal velocity heterogeneity beneath the trench zone itself produces subhorizontally-propagating waves that should be observed as coherent dipping events in receiver functions (RF). Due to similar RF delay times and moveouts, these events could be difficult to distinguish from backscattered P- and S-wave modes. To further verify this suggestion, we performed a full-waveform, 3-D visco-elastic finite-difference modelling of teleseismic wave propagation within a simplified model of a subduction zone. The synthetics show strong scattering from the area beneath the trench, dominated by the mantle and crustal P-waves propagating at 6.2–8.1 km/s and slower. These scattered waves occupy the same time and moveout intervals as the backscattered converted modes, and also have similar amplitudes. Although their amplitude decay characters are different, the uncertainty in the knowledge of the velocity and density structure of the subduction zone could make distinguishing between these modes difficult. However, under minimal assumptions, recent observations of receiver function amplitudes decreasing away from the trench support the interpretation of (sub-) trench-zone scattering.Although still limited in its representation of crustal heterogeneity, 3-D modelling suggests that scattering from near-Moho crustal structures plays a key role in the formation of teleseismic wavefields. Recognition of scattered noise in teleseismic records could help to constrain major crustal structures, particularly those with strong horizontal velocity contrasts at near-Moho depths, such as crustal sutures, subduction fault zones, and mountain roots. Matching of the observed arrivals with wavefield synthetics could help constrain the locations and parameters of such structures and also help substantiate the interpretations.  相似文献   

Identification of critical ground motions for seismic performance assessment of structures   总被引：1，自引：0，他引：1  

Rajesh P. Dhakal  John B. Mander  Naoto Mashiko 《地震工程与结构动力学》2006,35(8):989-1008

A method is established to identify critical earthquake ground motions that are to be used in physical testing or subsequent advanced computational studies to enable seismic performance to be assessed. The ground motion identification procedure consists of: choosing a suitable suite of ground motions and an appropriate intensity measure; selecting a computational tool and modelling the structure accordingly; performing Incremental Dynamic Analysis on a non‐linear model of the structure; interpreting these results into 50th (median) and 90th percentile performance bounds; and identifying the critical ground motions that are close to these defining probabilistic curves at ground motion intensities corresponding to the design basis earthquake and the maximum considered earthquake. An illustrative example of the procedure is given for a reinforced concrete highway bridge pier designed to New Zealand specifications. Pseudodynamic tests and finite element based time history analyses are performed on the pier using three earthquake ground motions identified as: (i) a Design Basis Earthquake (10% probability in 50 years) with 90 percent confidence of non‐exceedance; (ii) a Maximum Considered Event (2% probability in 50 years) representing a median response; and (iii) a Maximum Considered Event representing 90 percent confidence of non‐exceedance. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Analysis of the heliospheric current sheet fine structure: Single or multiple current sheets     

J.J. Blanco  J. Rodríguez-Pacheco  M.A. Hidalgo  J. Sequeiros 《Journal of Atmospheric and Solar》2006,68(18):2173-2181

When studying the heliospheric current sheet (HCS) local structure, it is not unusual to find wide HCS crossings. In this paper, we present one crossing that appears to have a complex internal structure composed of three parallel sheets and several possible HCS crossings that are consecutive and are on the order of minutes. Depending on their origin, different scenarios can explain multiple current sheets such as complex structures of helmet streamer at the Corona flowing into the solar wind, local waviness in the HCS structure, local oscillations of the HCS, and inverted magnetic fields or planar magnetic structures (PMS) close to the HCS. Distinguishing among these scenarios using just one observational point is very difficult because all of them are 3D structures. Nevertheless, we think that nearly parallel sheets are more likely in the first and in the last scenarios, i.e. multiple helmet streamer structure and PMS. In order to make the distinction between them, we have studied the possible reversal in the Q_e·B sign for every event. Our results suggest that the existence of not-wide HCS composed of multiple parallel sheets cannot be rejected.  相似文献   

Electric field effects on ionospheric and thermospheric parameters above the EISCAT station for summer conditions     

V. V. Klimenko  Yu. N. Korenkov  M. Förster 《Annales Geophysicae》1998,16(10):1200-1211

Numerical calculations of the thermospheric and ionospheric parameters above EISCAT are presented for quiet geomagnetic conditions in summer. The Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) was used. The numerical results were obtained both with a self-consistent calculation of the electric fields of magnetospheric and dynamo-action origin and with the magnetospheric electric fields only. It was found that the dynamo-electric field has some effect on the ionospheric convection pattern during quiet geomagnetic conditions. It has a marked effect mainly on the zonal neutral wind component above EISCAT (±20m/s at 140 km altitude). We have studied the effects of various field-aligned current (FAC) distributions on thermosphere/ionosphere parameters and we show that a qualitative agreement can be obtained with region-I and -II FAC zones at 75° and 65° geomagnetic latitude, respectively. The maximum FAC intensities have been assumed at 03–21 MLT for both regions with peak values of 2.5 × 10^–7 Am^–2 (region I) and 1.25 × 10^–7 A m^–2 (region II). These results are in agreement with statistical potential distribution and FAC models constructed by use of EISCAT data. The lack of decreased electron density in the night-time sector as observed by the EISCAT radar was found to be due to the spatial distribution of ionospheric convection resulting from electric fields of magnetospheric origin.  相似文献