Relationship between solar-flare hard X-ray sources and magnetic TP singularities     

O. G. Den  I. V. Zimovets 《Astronomy Reports》2014,58(7):488-496

The impulsive phase of the powerful solar flare of September 13, 2005 (～23:18–23:21 UT) observed in hard X-rays (～25–300 keV) by the RHESSI spacecraft is analyzed. The spatial locations of numerous X-ray sources are compared with the locations of Transition Point (TP) singularities in the magnetic field calculated for flare regions. It is shown that the hard X-ray sources are related to TP singularities, i.e., to possible locations of primary flare energy release. Magnetic field lines expelled from the vicnity of these magnetic singularities end in the chromosphere, near hard X-ray sources. The question of how these multiple magnetic singularities are involved virtually simultaneously in the energy-release process requires further study.  相似文献   

Landslide consequence analysis: a region-scale indicator-based methodology   总被引：1，自引：1，他引：0  

A. Puissant  M. Van Den Eeckhaut  J.-P. Malet  O. Maquaire 《Landslides》2014,11(5):843-858

Consequence analysis is, together with hazard evaluation, one of the major steps of landslide risk assessment. However, a significant discrepancy exists between the number of published landslide hazard and landslide consequence studies. While various methodologies for regional-scale hazard assessment have been developed during the last decade, studies for estimating and visualising possible landslide consequences are still limited, and those existing are often difficult to apply in practice mainly because of the lack of data on the historical damage or on landslide damage functions. In this paper, an indicator-based GIS-aided methodology is proposed with an application to regional-scale consequence analysis. The index, called Potential Damage Index, allows describing, quantifying, valuing, totalizing and visualising different types of consequences. The method allows estimating the possible damage caused by landslides by combining weighted indicators reflecting the exposure of the elements at risk. Direct (physical injury, and structural and functional damage) and indirect (socio-economic impacts) consequences are individually analysed and subsequently combined to obtain a map of total consequences due to landsliding. Geographic visualisation of the index allows the delineation of the areas exposed to any type of possible impacts that could be combined with a corresponding map displaying landslide probability of occurrence. The method has been successfully applied to analyse the present consequences in the Barcelonnette Basin (South French Alps). These maps contribute to development of adequate land use and evacuation plans, and thus are important tools for local authorities and insurance companies.  相似文献   

The age and palæoenvironmental significance of the Kalahari Sands in western Zimbabwe: a thermoluminescence reconnaissance study     

Kennedy Munyikwa  Peter Van Den Haute  Dimitri Vandenberghe  Frans De Corte 《Journal of African Earth Sciences》2000,30(4):199

Thermoluminescence (TL) dating, has been applied to 10 samples from the æolian Kalahari Sands of western Zimbabwe using the total bleach (additive dose) and regeneration techniques on coarse-grain quartz separates. The results suggest that the main phases of sand accumulation occurred between 10 and 96 ka. This Upper Pleistocene age is consistent with current opinions and argues against an important period of Holocene æolian activity. The oldest sands were found in the Victoria Falls area where they overlie a ferricrete horizon. Based on our age determinations, we were able to constrain the age of this horizon to between 96±8 and 160±23 ka, which approximately coincides with the Last Integlaciation in the high latitudes. The youngest ages were obtained for sands from the southeastern part of the Hwange dune field but our limited sampling permits assigning only a minimum age of ca 20 ka to the ferricrete horizon observed in this area. Thus, we cannot ascertain if this ferricrete horizon is isochronous with the one at Victoria Falls or if it developed during a younger humid phase.Dune building activity most probably occurred in recurrent cycles of aridity interspersed with periods during which æolian activity was limited or non-existent. Unfortunately, besides the ferricrete horizons, no other stratigraphical evidence of climatic fluctuation has been observed in the study area. However, it is possible that palæosols have been entirely eroded before the subsequent deposition of new sediment, resulting in an incomplete stratigraphical record. The possibilities and limitations of luminescence dating for elucidating phases of climatic fluctuation in such situations are discussed briefly. In addition, we noticed serious discrepancies between the results yielded by the different techniques that were used for determining the dose rate. Hence, further work is needed to validate the accuracy of our dose rate measurements that may cause our TL ages to be about 30% too young.  相似文献   

大巴山地区铂矿地质特征及成因初探   总被引：6，自引：1，他引：5  

唐将  邓富银 《矿产与地质》2000,14(2):86-90

大巴山铂矿产于秦岭地槽与扬子准地台的接合部位——城巴深断裂两侧的断块或岩体蚀变破碎带中 ,含矿层为上震旦统至下寒武统黑色岩系 ,含矿围岩具黄铁矿化、硅化、碳化现象。成矿物质来源、矿源初始富集与聚积成矿均与城巴深断裂的多期活动及早期火山喷发、多期岩浆侵入关系密切  相似文献   

松嫩平原西部盐沼的形成与演化   总被引：21，自引：5，他引：16  

李取生  邓伟  钱贞国 《地理科学》2000,20(4):362-367

本文运用环境变迁的理论和方法,较系统地分析了松嫩平原西部盐沼的形成与演变机制。本区沼泽形成的主要控制因素是古河道变迁、新构造运动、风力作用、古气候变化。沼泽残余盐碱化与晚更新世松辽大湖的消亡、河道变迁有关,现代盐碱化则主要是水利工程、植被破坏和气候变化引起的,而且呈迅速加剧的趋势。防治沼泽盐碱化的主要措施是实施水稻和芦苇开发、大规律建立蓄洪区和自然保护区。  相似文献   

Interpretation of Crown Radiation Temperatures of a Dense Douglas fir Forest with Similarity Theory     

Fred C. Bosveld  A. A. M. Holtslag  B. J. J. M. Van Den Hurk 《Boundary-Layer Meteorology》1999,92(3):429-451

Infrared crown radiation temperatures as observed over a dense Douglas fir forest are analyzed in the context of similarity theory and the concept of transport resistances. As such we obtain a rather high value of the roughness length for heat, which is about equal to the roughness length for momentum. This value can be explained by the more efficient transport of heat relative to momentum in the roughness sublayer of the forest. Correcting for this effect we arrive at the classic value for homogeneous terrain of about 0.1 times the roughness length for momentum. For unstable cases the presence of enhanced mixing of heat in the roughness sublayer leads to a modified integral stability function for the dimensionless potential temperature difference between the surface and the top of the roughness sublayer. The observations give some evidence for this different stability behaviour. The analysis suggests that during daytime the radiative surface temperature and the aerodynamic surface temperature are not significantly different when used to estimate fluxes. Daytime trunk space air temperature is satisfactory parameterized with the concept of gusts and with surface renewal analysis. As such it is related to the sensible heat flux and the storage heat flux. Night time radiation temperatures at times strongly deviate from the expected behaviour based on similarity theory and the roughness length for heat, suggesting that the concept of a single surface temperature is too simple for such cases.  相似文献   

Modelling of drainage dynamics influence on sediment routing system in a fold‐and‐thrust belt     

Marc Viaplana‐Muzas  Julien Babault  Stphane Dominguez  Jean Van Den Driessche  Xavier Legrand 《Basin Research》2019,31(2):290-310

Drainage networks link erosional landscapes and sedimentary basins in a source‐to‐sink system, controlling the spatial and temporal distribution of sediment flux at the outlets. Variations of accumulation rates in a sedimentary basin have been classically interpreted as changes in erosion rates driven by tectonics and/or climate. We studied the interactions between deformation, rainfall rate and the intrinsic dynamics of drainage basins in an experimental fold‐and‐thrust belt subjected to erosion and sedimentation under constant rainfall and shortening rates. The emergence of thrust sheets at the front of a prism may divert antecedent transverse channels (perpendicular to the structural grain) leading to the formation of longitudinal reaches, later uplifted and incorporated in the prism by the ongoing deformation. In the experiments, transverse incisions appear in the external slopes of the emerging thrust sheets. Headward erosion in these transverse channels results in divide migration and capture of the uplifted longitudinal channels located in the inner parts of the prism, leading to drainage network reorganization and modification of the sediment routing system. We show that the rate of drainage reorganization increases with the rainfall rate. It also increases in a nonlinear way with the rate of uplift. We explain this behaviour by an exponent > 1 on the slope variable in the framework of the stream power erosion model. Our results confirm the view that early longitudinal‐dominated networks are progressively replaced by transverse‐dominated rivers during mountain building. We show that drainage network dynamics modulate the distribution of sedimentary fluxes at the outlets of experimental wedges. We propose that under constant shortening and rainfall rates the drainage network reorganization can also modulate the composition and the spatial distribution of clastic fluxes in foreland basins.  相似文献