Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

Data from HF-radars are used to make the first simultaneous conjugate measurements of the day-side reconnection electric field. A period of 4 h around local magnetic noon are studied during a geospace environment modeling (GEM) boundary layer campaign. The interplanetary magnetic field (IMF) was southward whilst the eastward component (By) was variable. The flow patterns derived from the radar data show the expected conjugate asymmetries associated with IMF |By| ≥ 0. High-time resolution data (50 and 100 s) enable the flow of plasma across the open/closed field line boundary (the separatrix) to be studied in greater detail than in previous work. The latitude of the separatrix follows the same general trend in both hemispheres but shows a hemispherical difference of 4°, with the summer cusp at higher latitude, as expected from dipole tilt considerations. However, the short-time scale motion of the separatrix cannot be satisfactorily resolved within the best resolution (300 m s⁻¹) of the experiment. The orientation of the separatrix with respect to magnetic latitude is found to follow the same trend in both hemispheres and qualitatively fits that predicted by a model auroral oval. It shows no correlation with IMF By. However, the degree of tilt in the Northern (summer) Hemisphere is found to be significantly greater than that given by the model oval. The convection pattern data show that the meridian at which throat flow occurs is different in the two hemispheres and is controlled by IMF By, in agreement with empirically derived convection patterns and theoretical models. The day-side reconnection electric field values are largest when the radar’s meridian is in the throat flow or early afternoon flow regions. In the morning or afternoon convection cells, the reconnection electric field tends to zero away from the throat flow region. The reconnection electric field observed in the throat flow region is bursty in nature.     

Response of the reconnection electric field and polar cap potential to the IMF and velocity of solar wind

It is well known that the cross polar cap potential is saturated under a strong interplanetary electric field and is often said to be related to the ionospheric currents. To investigate the other factors influencing this phenomenon, a global magnetohydrodynamics simulation not including the feedback from the ionosphere to the magnetosphere was conducted. The simulation results showed that an increase in the southward IMF causes a smaller increase in the cross polar cap potential than that caused by an increase in the solar wind velocity. This difference was caused by the transportation of reconnected magnetic field lines towards the tail.     

Ionospheric effects of ground motion: The roles of magnetic field and nonlinearity

Transformation of infrasound to magnetic sound upon propagation from ground level up to the ionosphere is considered. It is shown that upon entering the ionospheric layers at altitudes of order 150–170 km, the wave dynamics changes sharply. Nonlinear effects, including shock formation, are also considered. The shocks are typically formed in a relatively narrow range of altitudes, or not formed at all. Generalization of the model to a case of oblique propagation is briefly considered, and the effects of atmospheric profile variation and of finite plasma conductivity are estimated. Along with providing qualitative insight, the model gives some realistic estimates for waves generated by earthquakes.     

Weimer电场模式在地球磁层内的特征

地球磁层中的电场是研究磁层物理的重要参数,目前常用的对流电场有均匀晨昏电场和投影电场.电离层电场可以看做磁层电场沿磁力线在电离层的投影,本文选取的电离层电场模型为Weimer(2001模式)电场.利用T96磁场模式,沿磁力线将电离层电场投影到磁层空间,得到一个新的磁层电场模式,并讨论了磁暴、行星际磁场(IMF)、太阳风参数和亚暴等对磁层电场的影响.利用该模型计算的电场结果与卫星探测结果相符.     

行星际-赤道电场穿透效率的数值模拟研究

电场穿透作为强烈地磁活动期间太阳风-磁层-电离层电动力学耦合的重要形式,近年来一直是空间物理学最为活跃的课题之一.在过去的近40年里人们一直关注于观测证据的寻找以及物理过程的模拟,“电场穿透效率”这一重要定量化指标直到最近几年才得到重视.本文定义赤道电场增量与对应的行星际电场增量的比值为穿透效率,通过数值模拟的方法对穿透效率的地方时变化以及与中性风发电机的关系做了实验性讨论,在一定简化条件下结果表明：（1）不考虑跨极盖电势饱和的情况下,赤道电场增量与行星际电场增量呈线性关系,且中性风发电机并不影响电场穿透效率;（2）恒定重联线长度L的限定下,穿透效率具有明显地方时依赖性.例如对于L=2.6 RE,在9LT至23LT之间,穿透效率维持在10％左右;0LT至7LT之间,穿透效率迅速从2％上升至30％后又迅速回落到原始水平,形成尖峰.这些结果基本符合观测特征.     

A conceptual model of the relationship between channel characteristics and discharge

Regression equations with the form y = f(q), where y is a channel characteristic and q is a discharge of a particular frequency are widely used in fluvial geomorphology. They imply that channel geometry is related to a dominant discharge. For this to be so, the river must be ‘in regime’ i.e. its characteristics must fluctuate about a mean condition which is effectively stationary at the time scale considered. The static regression-dominant discharge approach does not fully describe the relationship between channel characteristics and discharge and an alternative model is proposed with the form y(t) = ∞ h(u)- q(t-u)du. This model states that channel form is a product of the whole series of discharges experienced by the channel. The dominant discharge-static regression approach provides a working approximation of the relationship between channel characteristics and discharge only when temporal variations in q are small or when y is insensitive to variations in q.     

地震电离层异常电场模拟及初步研究

强地震会造成电离层电场发生异常变化.基于大气层-电离层电动力学理论对地震电离层异常电场开展数值模拟和研究,将理论推导出来的电离层异常电场方程扩展到球面坐标系中,并且考虑到电离层层电导率的各向异性,建立新的地震电离层异常电场模式.引进一个电离层层电导率经验公式(Nopper and Carovillano,1979),对中低纬度地震电离层异常电场特性进行数值模拟.模拟结果表明:附加电流引起电离层异常电场范围远大于自身在地表上的分布.且发生在低纬地区的异常电场主要成分是纬向电场,在东西两侧显偶极子分布.在额外电流分布相同的情况下,夜晚生成的异常电场更显著,存在昼夜差异.     

A conceptual model of wind erosion of soil surfaces by saltating particles

A conceptual model is described for the prediction of wind erosion rates dependent on the distribution of impact energy delivered to the surface by saltating grains, P[Ei], and the distribution of local surface strength, P[Es]. Methods are presented for the measurement of both distributions and consequent loss of material from the bed. It is concluded that saltating sand grains can rupture weak crusts under even moderate wind conditions, and that the rate of erosion will depend on the shape of the distribution tails. Copyright © 1999 John Wiley & Sons, Ltd.     

Factors shaping submerged bryophyte communities: A conceptual model for small mountain streams in Germany

Several models explaining species composition of aquatic bryophytes are available for specific regions. However, a more general, conceptual model applicable to a broader range of regions is lacking.We present a conceptual model ranking environmental factors determining submerged bryophyte communities in small mountain streams. It was tested on a dataset of 54 stream sections after removing the effect of stream size and altitude. Species responses were modeled with pH as predictor variable based on 97 stream sites covering six mountain regions all over Germany. Multiple regressions revealed the importance of primary growth factors (light, Ep(CO₂)) and substrate for the total submerged bryophyte coverage.The known distinction of hard- and softwater bryoflora was clearly supported. The floristic composition of headwaters was predominantly determined by the bicarbonate/ionic strength complex. Species response to pH values supported this result and thus our conceptual model. The primary growth resources light, Ep(CO₂) and availability of coarse streambed material explained one third (R_adjusted² = 0.34) of total submerged bryophyte cover. Disturbances, predominantly spates, reduce biomass but do not affect the basic floristic structure.In conclusion, conceptual models and monitoring methods focusing on aquatic bryophytes need to clearly distinguish “aquatic” from “submersed by chance”. All “aquatic bryophytes” found in Germany can also occur at least temporarily at non-submerged sites. Therefore, a distinction between primary growth factors and additional resources is recommended to disentangle factors determining aquatic bryophyte communities.     

A conceptual model for the longitudinal distribution of wood in mountain streams

Wood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel‐, valley‐ and watershed‐scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non‐randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non‐randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range. Copyright © 2009 John Wiley & Sons, Ltd.     

New model of polarization of rocks: Theory and application

Mathematical modeling of a little known model of induced polarization (IP) referred to as “induced polarization caused by constrictivity of pores” was developed. Polarization occurs in all types of rocks if surface areas and transfer numbers are different for connected pores. During the polarization process, all contacts between pores of different transfer numbers will be blocked and the electrical current will flow through the remaining channels. Diffusion equations with different specified boundary conditions for time-on and time-off have been used to develop the base of this model. The new algorithm was tested on laboratory measurements. Several samples were selected: shale, mudstone, tillite, hematite, lava, and manganese ore. Each theoretical model includes pores of more than 40 different sizes sporadically distributed in the sample. The obtained data show good agreement with theory and provide new information about pore size distribution in samples, prevalent pore radius, and effect of anisotropy.     

A statistical model of the geomagnetic field

Summary A statistical model of the geomagnetic field is derived, based on the assumption of an axial geocentric dipole field of strengthH _e at the equator perturbed by randomly directed components of constant magnitudeh. The model fits the dispersions found from an analysis of the 1945 field, and the ratioh/H _e obtained for this field and from the palaeomagnetic data both average to about 0.4. The model predicts that during reversal of the dipole field, the field intensity falls to between 0.2 and 0.4 of the steady field intensity, and this agrees with estimates made from the palaeomagnetic observations.     

2008年1月5日磁层亚暴期间磁尾近地重联事件的THEMIS观测与分析

本文主要应用THEMIS卫星的磁场和等离子体流观测数据,分析了2008年1月5日08∶51~08∶57 UT亚暴膨胀相期间磁尾的一个近地重联事件.在亚暴膨胀相期间,地面的全天空成像仪清楚地记录到了极光的极向扩展,THEMIS的P5卫星在地球同步轨道附近观测到了磁场的偶极化现象.在亚暴膨胀相末期的08∶51~08∶57 UT期间,P3(X_GSM~-9.12R_E) 和P4 (X_GSM ~-9.40R_E) 同时观测到了一对方向相反的高速等离子体流.这对方向相反的高速等离子体流是由磁尾的重联现象所引起.重联的位置被估计位于X_GSM ~-9.12R_E 和X_GSM~-9.40R_E之间较小的空间范围内.并且,在重联位置的两侧,重联的Hall效应被P3和P4两颗卫星观测到.因此,这一磁尾重联事件发生在距离地球非常近的空间范围内.     

A new conceptual model for whole mantle convection and the origin of hotspot plumes

A new conceptual model of mantle convection is constructed for consideration of the origin of hotspot plumes, using recent evidence from seismology, high-pressure experiments, geodynamic modeling, geoid inversion studies, and post-glacial rebound analyses. This conceptual model delivers several key points. Firstly, some of the small-scale mantle upwellings observed as hotspots on the Earth's surface originate at the base of the mantle transition zone (MTZ), in which the Archean granitic continental material crust (TTG; tonalite-trondhjemite-granodiorite) with abundant radiogenic elements is accumulated. Secondly, the TTG crust and the subducted oceanic crust that have accumulated at the base of MTZ could act as thermal or mechanical insulators, leading to the formation of a hot and less viscous layer just beneath the MTZ; which may enhance the instability of plume generation at the base of the MTZ. Thirdly, the origin of some hotspot plumes is isolated from the large low shear-wave velocity provinces (LLSVPs) under Africa and the South Pacific. I consider that the conceptual model explains why almost all the hotspots around Africa are located above the margins of the African LLSVP. Because a planetary-scale trench system surrounding a “Pangean cell” has been spatially stable throughout the Phanerozoic, a large amount of the oceanic crustal layer is likely to be trapped in the MTZ under the Pangean cell. Therefore, under Africa, almost all of the hotspot plumes originate from the base of the MTZ, where a large amount of TTG and/or oceanic crusts has accumulated. This conceptual model may explain the fact that almost all the hotspots around Africa are located on margins above the African LLSVP. It is also considered that some of the hotspot plumes under the South Pacific thread through the TTG/oceanic crusts accumulated around the bottom of the MTZ, and some have their roots in the South Pacific LLSVP while others originate from the MTZ. The numerical simulations of mantle convection also speculate that the Earth's mantle convection is not thermally double-layered at the ringwoodite to perovskite + magnesiowüstite (Rw → Pv + Mw) phase boundary, because of its gentle negative Clapeyron slope. This is in contrast with some traditional images of mantle convection that have independent convection cells between the upper and lower mantle. These numerical studies speculate that the generation of stagnant slab at the base of the MTZ (as seismically observed globally) may not be due to the negative Clapeyron slope, and may instead be related to a viscosity increase (i.e., a viscosity jump) at the Rw → Pv + Mw phase boundary, or to a chemically stratified boundary between the upper and the lower mantle, as suggested by a recent high-pressure experiment.     

Problem of the nature of the sunrise effect in diurnal variations in the electric field in Kamchatka: 1. Time variations in the electric field

The effect of sunrise in time variations in the electric field in the near-Earth atmosphere at the Kamchatka Paratunka observatory has been studied. Twenty-nine records under fair-weather conditions have been selected. It has been indicated that the estimated effect parameters—the times of the effect’s onset and field strength maximum relative to the sunrise time, as well as the ratio of the strength maximum to its value before sunrise and the effect duration—coincide with the previously published data. Thereby, the conclusion is confirmed that the sunrise effect in diurnal variations in the electric field in the near-Earth atmosphere is related to the turbulence and convection processes in the atmospheric boundary layer at a change in atmospheric temperature.     

A contribution to the asymptotic expression of the electromagnetic field of an electric dipole

Studia Geophysica et Geodaetica - Были выведены...     

火星感应磁场模型及其磁力线分布

本文利用火星具有电离层而无内禀磁场的特点以及它与太阳风相互作用的性质,通过适当的假设,建立了火星感应磁场模型.此模型建立如下,利用电流连续的特性: Δ·j=0 (j为感应电流)以及对火星磁层中的电流体系分布的合理假设给出电流,并由毕奥—萨伐尔定理得到火星周围的磁场强度的表达式;利用我们自编的磁力线跟踪程序由求得的磁场强度得到火星周围的磁力线分布.我们发现:利用此火星磁场模型得到的火星周围的磁力线分布与卫星观测的结果以及其他方法得到的结果符合的很好.     

Nature of the sunrise effect in daily electric field variations at Kamchatka: 2. Electric field frequency variations

The power spectra of time variations in the electric field strength in the near-Earth’s atmosphere and in the geomagnetic field horizontal component, which were simultaneously observed at the Paratunka observatory (φ = 52°58.3′ N; λ = 158°14.9′ E) in September 1999, have been studied. The periods of the day (including sunrise, sunset, and night) have been considered. It has been indicated that oscillations with periods T ～ 2.0–2.5 h are present in the power spectra of these parameters during the day. The intensity of these oscillations increases noticeably and the oscillations in the band of periods T < 1 h increase simultaneously in the field strength power spectra at sunrise. The variations in the argument of the cross-spectrum of these parameters indicated that oscillations in the 2.0–2.5 h period band are caused by sources that are located above the ionospheric dynamo region; at the same time, oscillations in the 0.5–1 h period band are caused by sources in the lower atmosphere. A possible mechanism by which these oscillations are generated, related to the vortex motion of convective cells that originate at sunrise in the boundary atmospheric layer, is proposed.