Proton transport model in the ionosphere. 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam     

M. Galand  J. Lilensten  W. Kofman  D. Lummerzheim 《Annales Geophysicae》1998,16(10):1308-1321

We investigate the influence of magnetic mirroring and elastic and inelastic scattering on the angular redistribution in a proton/hydrogen beam by using a transport code in comparison with observations. H-emission Doppler profiles viewed in the magnetic zenith exhibit a red-shifted component which is indicative of upward fluxes. In order to determine the origin of this red shift, we evaluate the influence of two angular redistribution sources which are included in our proton/hydrogen transport model. Even though it generates an upward flux, the redistribution due to magnetic mirroring effect is not sufficient to explain the red shift. On the other hand, the collisional angular scattering induces a much more significant red shift in the lower atmosphere. The red shift due to collisions is produced by < 1 -keV protons and is so small as to require an instrumental bandwidth <0.2nm. This explains the absence of measured upward proton/hydrogen fluxes in the Proton I rocket data because no useable data concerning protons < 1 keV are available. At the same time, our model agrees with measured ground-based H-emission Doppler profiles and suggests that previously reported red shift observations were due mostly to instrumental bandwidth broadening of the profile. Our results suggest that Doppler profile measurements with higher spectral resolution may enable us to quantify better the angular scattering in proton aurora.  相似文献   

Particle fabric in a small, type-2 ignimbrite flow unit (Laacher See, Germany) and implications for emplacement dynamics     

Simon R. Hughes  Timothy H. Druitt 《Bulletin of Volcanology》1998,60(2):125-136

 Ignimbrites of the 13-ka Upper Laacher See Tephra were deposited from small, highly concentrated, moderately fluidized pyroclastic flows. Their unconsolidated nature, and the prominence of accidental Devonian slate fragments, make these ignimbrites ideal for clast fabric studies. The upper flow unit of ignimbrite M14 has characteristics typical of a type-2 ignimbrite. Layer 2a and the lower part of layer 2b of the flow unit have strong, upstream-inclined a[p] fabrics (a[p] means long particle axes parallel to flow direction). Only clasts with a/b axial ratios of 2.5 or greater preserve good a[p] fabrics, whereas the a–b planes of flat fragments dip upstream irrespective of axial ratio. The a-axis fabric becomes weaker, flatter, and more girdle-like in the upper half of layer 2b. At one locality the a-axis fabric appears to rotate 40° up through the flow unit, suggesting either shear decoupling of different levels in the moving flow or unsteadiness effects in a flow depositing progressively at its base. The existence of similarly strong a[p] fabrics in layer 2a and the lower half of layer 2b appears inconsistent with the common interpretation that ignimbrite flow units are emplaced as a plug of essentially non-shearing material (layer 2b) on a thin shear layer (layer 2a), and that the entire flow freezes en masse to form the deposit. The data suggest that, if the flow froze en masse, it was shearing pervasively through at least half its thickness. Another possibility is that the flow unit aggraded progressively from the base up, and that the fabrics record the integrated history of shear directions and intensities immediately above the bed throughout the duration of deposition. Received: 13 February 1997 / Accepted: 4 April 1998  相似文献   

A statistical study of field-aligned electron beams associated with ion conies events     

W. Miyake  T. Mukai  N. Kaya 《Annales Geophysicae》1998,16(8):940-947

A statistical study of field-aligned electron beams associated with upflowing ion conics is presented from Exos-D (Akebono) observations below 10 000 km. The electron beams are narrowly collimated along the field line and generally have energies of several tens of eV. They are divided in the analysis into three types: upflowing, downflowing, and counterstreaming. All the types of electron beams are almost equivalent in their energy and pitch angle characteristics and their association rate with upflowing ion events. About 50% of ion conies are found to be coincident with field-aligned electron beams. There is also a correlation in energy between the field-aligned electrons and ion conics. These show that the association is not a mere coincidence but rather that the field-aligned acceleration of electrons is related to the perpendicular energization of ions. The association rate of upflowing electrons is high on the nightside, while that of downflowing electrons is high on the dayside. The association rate of downflowing electrons is high at low altitudes, and the rates of the three types of electron beams become equivalent at high altitudes. Data indicate that the height of the electron acceleration region is lower on the nightside. It is suggested that the average height of the electron acceleration region is around the satellite apogee (–10000 km), and the average thickness of the region is about thousands km.  相似文献   

淮南煤矿塌陷区煤矸石填充复垦及其对环境的影响   总被引：18，自引：0，他引：18  

崔龙鹏 《安徽地质》1998,(3)

在分析淮南矿区煤矸石和地面塌陷现状的基础上,探讨用煤矸石填充塌陷区的意义及其对环境的影响。  相似文献   

The importance of energetic particle precipitation on the chemical composition of the middle atmosphere   总被引：1，自引：0，他引：1  

Richard Mansergh Thorne 《Pure and Applied Geophysics》1980,118(1):128-151

An assessment is made of the relative contribution of certain classes of energetic particle precipitation to the chemical composition of the middle atmosphere with emphasis placed on the production of odd nitrogen and odd hydrogen species and their subsequent role in the catalytic removal of ozone. Galactic cosmic radiation is an important source of odd nitrogen in the lower stratosphere but since the peak energy deposition occurs below the region where catalytic removal of O₃ is most effective, it is questionable whether this mechanism is important in the overall terrestrial ozone budget. The precipitation of energetic solar protons can periodically produce dramatic enhancement in upper stratospheric NO. The long residence time of NO in this region of the atmosphere, where catalytic interaction with O₃ is also most effective, mandates that this mechanism be included in future modelling of the global distribution of O₃. Throughout the mesosphere the precipitation of energetic electrons from the outer radiation belt (60°70°) can sporadically act as a major local source of odd hydrogen and odd nitrogen leading to observable O₃ depletion. Future satellite studies should be directed at simultaneously measuring the precipitation flux and the concomitant atmosphere modification, and these results should be employed to develop more sophisticated models of this important coupling.  相似文献   

A Lagrangian stochastic model for the trajectories of particle pairs and its application to the prediction of concentration variance within plant canopies     

A. M. Reynolds 《Boundary-Layer Meteorology》1998,88(3):467-478

A simple Lagrangian stochastic model for the trajectories of particle pairs in high Reynolds-number turbulent flows is presented. In this model, the velocities of particle pairs are initially correlated but subsequently each particle moves independently. The independent single-particle trajectories are simulated using Thomson's model [J. Fluid Mech. 180, 529–556, 1987]. This two-particle model exactly satisfies the well-mixed condition for Gaussian turbulence when length scales, characterizing the two-point Eulerian velocity correlation function, vanish. Temperature variances, due to heat released as a passive scalar from an elevated plane source, within a model plant canopy (Coppin et al. Boundary Layer Meteorol. 35, 167–191, 1986) are shown to be well predicted by the model. It is suggested that for strongly inhomogeneous flows, the two-point Eulerian velocity function is of secondary importance in determining the simulated trajectories of particle pairs compared to the importance of ensuring satisfaction of the two-to-one constraint (Borgas and Sawford. J. Fluid Mech. 279, 69–99, 1994); i.e ensuring that one-particle statistics obtained from the two-particle model are the same as those obtained from the corresponding one-particle model. Limitations of this modelling approach are discussed.  相似文献   

Further discussion on the intercomparison of the trace metal concentrations and particle size of fluvial sediment recovered from two centrifuge systems     

S. Santiago  R. L. Thomas  J.-L. Loizeau  P.-Y. Favarger  J.-P. Vernet 《水文研究》1990,4(3):283-287

A single large volume water sample taken at the mouth of the Upper Rhone River on Lake Geneva was processed directly in parallel through two continuous flow centrifuges, a Westphalia and an Alfa-Laval. Sediment was recovered from the Westphalia, and separately from the bowl and brass core of the Alfa-Laval. The three sediment samples were analyzed for particle size and the following elements: Zn, Cu, Mn, Cr, P, Co, B, V, Be, Sr, Na, Pb, Ni, Ba, Fe, Ca, and Mg. Results indicate that the particle size recovery of both machines is similar when sediment from the brass core and bowl of the Alfa-Laval are combined, and that the recovery for all elements other than Cu, V, B, and Pb are the same when the particle size differences are taken into account. Sediment from the Alfa-Laval brass core is clearly contaminated by Cu, B and is also elevated in V and Pb but not to a significant extent. The sediment recovered from the bowl of the Alfa-Laval is contaminated only with Cu, with a 10 ppm increase over the 52 ppm recovered in the Westphalia sediment. Operating procedures involve the discarding of the brass core sediment and the mixing of the Alfa-Laval bowl sediment with that from the Westphalia. The consequent increase in Cu is estimated at less than 5 ppm or within the confidence level of the analysis. These procedures are recommended to all operators of non modified Alfa-Laval units.  相似文献   

多波束海底地形数据空值区域的插值填补方法分析     

樊妙  卢惠泉  邢喆  金继业 《海洋测绘》2015,35(1):11-13

由于边界误差剔除、测线布设过于稀疏等因素影响,利用多波束数据生成高分辨率DEM时,常常会存在一些水深空值单元或区域。为了对这些数据空值区域进行可靠填补,在考虑地形特征及空值单元大小的情况下,利用IDW、Spline、Kriging、TIN四种插值方法对某区域多波束海底DEM空值区域进行直接内插填补试验,结果表明插值算法的选取不仅受地形类型限制,而且与空值区域的大小也密切相关。  相似文献   

Sheath effects on DEMETER ion drift measurements     

Richard Marchand  Nelson Knutson 《Planetary and Space Science》2010,58(10):1365-1373

The “Instrument d’Analyse du Plasma” on DEMETER includes an ion drift meter used to measure the direction of the incoming ram plasma ( [Berthelier et al., 2006a] and [Berthelier et al., 2006b]). Given the velocity of the satellite, and expected flow velocities of plasma along DEMETER's orbit, it is estimated that at mid latitudes, the direction of incident plasma as measured by IAP should be within approximately 2° of the ram direction. Yet, significantly larger angular deviations are measured routinely. An important assumption made in the interpretation of onboard instruments, such as IAP, is that neither the spacecraft nor the instrument significantly perturb the plasma that is being measured. In view of the large observed angular deviations, this paper examines the possible effect of the electrostatic sheath surrounding IAP. This is done with the 3D PIC simulation code PTetra. The model uses a full 3D particle in cell code with unstructured tetrahedral mesh capable of accurately representing the satellite geometry. The mesh is also adaptive so as to provide a fine spatial resolution in the vicinity of the particle sensor where it is needed, and a coarse resolution in regions where plasma parameters vary over a longer scale length. Calculation results show that while particle deflection associated with the electrostatic sheath near IAP can account for appreciable angular deflections for representative ionospheric plasmas, they are typically smaller than the ones observed. Additionally, the model is unable to reproduce the latitudinal dependence of the observed large deflection angles. It is concluded that sheath effects may cause appreciable distortions on the IAP type of ion flow meter instruments, and on other particle sensors in general. The larger observed deviations and their latitudinal dependence, however, must be attributable to other physical processes not accounted for in the model.  相似文献   

塔河油田奥陶系碳酸盐岩油藏溶洞充填物特征   总被引：4，自引：0，他引：4  

徐微  蔡忠贤  贾振远  林忠民 《现代地质》2010,24(2)

塔河油田奥陶系缝洞型储层是该区最重要的油气生产层段,古岩溶作用产生的大量溶洞作为油气的存储空间,具有举足轻重的意义。通过对11口井充填溶洞的岩心观察,划分出化学沉(淀)积岩相、搬运型岩相、垮塌型岩相、渗流充填相4大类溶洞充填相。搬运型岩相为溶洞的早期充填产物,当地表岩溶的溶蚀作用发展到一定程度时岩石会发生崩落,崩落的结果就产生了垮塌型岩相,后期的渗流充填相以填隙物的形式充填在垮塌型岩相里。据区内Ta井的典型溶洞充填特征,归纳出其充填序列为上部的溶洞破裂相、中部的塌陷相及下部的海水侵入充填相。溶洞充填物中微量元素、稀土元素等的地球化学特征,证实区内存在海水-淡水混合岩溶,对油田的开发生产具有很好的指导意义。  相似文献