Optical tomography of the aurora and EISCAT

Tomographic reconstruction of the three-dimensional auroral are emission is used to obtain vertical and horizontal distributions of the optical auroral emission. Under the given experimental conditions with a very limited angular range and a small number of observers, algebraic reconstruction methods generally yield better results than transform techniques. Different algebraic reconstruction methods are tested with an auroral are model and the best results are obtained with an iterative least-square method adapted from emission-computed tomography. The observation geometry used during a campaign in Norway in 1995 is tested with the are model and root-mean-square errors, to be expected under the given geometrical conditions, are calculated. Although optimum geometry was not used, root-mean-square errors of less than 2% for the images and of the order of 30% for the distribution could be obtained. The method is applied to images from real observations. The correspondence of original pictures and projections of the reconstructed volume is discussed, and emission profiles along magnetic field lines through the three-dimensionally reconstructed arc are calibrated into electron density profiles with additional EISCAT measurements. Including a background profile and the temporal changes of the electron density due to recombination, good agreement can be obtained between measured profiles and the time-sequence of calculated profiles. These profiles are used to estimate the conductivity distribution in the vicinity of the EISCAT site. While the radar can only probe the ionosphere along the radar beam, the three-dimensional tomography enables conductivity estimates in a large area around the radar site.Former address: MPE Garching     

基于注意力机制LSTM的电离层TEC预测

电离层总电子含量(Total Electron Content,TEC)的监测与预报是空间环境研究的重要内容,对卫星通讯和导航定位等有重要意义.TEC值影响因素较多,很难确定精确物理模型来对其进行预测.本文设计了基于注意力机制的LSTM模型(Att-LSTM),采用过去24小时TEC观测数据对未来TEC进行预测.选择北半球东经100°上,每2.5°纬度选择一个位置,共计36个位置来验证本文提出模型的性能,并与主流的深度学习模型如DNN、RNN、LSTM进行对比实验.取得了如下成果：(1)在选定的36个地区未来2小时单点预测上,基于本文的Att-LSTM模型的TEC预测性能明显优于其他对比模型;(2)讨论了纬度对Att-LSTM预测未来2小时TEC值时性能的影响,发现在北纬0°到60°之间,Att-LSTM预测性能随着纬度的升高而略有降低,在北纬62.5°~87.5°之间,模型预测性能出现扰动,预测效果略差;(3)讨论了磁暴期和磁静期模型的预测性能,发现无论是磁暴期还是磁静期,本文模型预测性能均较好;(4)还讨论了对未来多时点预测效果,实验结果表明,本文所提出的模型对未来2、4个小时的预测拟合度R-Square均超过0.95,预测结果比较可靠,对未来6、8、10个小时预测拟合度最高为0.7934,预测拟合度R-Square下降迅速,预测结果不可靠.

     

Heating of beam ions by ion acoustic waves

Satellite measurements show that ion beams above the auroral acceleration region are heated to hundreds of eV in a direction perpendicular to the magnetic field. We show that ion acoustic waves may be responsible for much of this heating. Even in the absence of a positive slope in the velocity distribution of the beam ions, ion acoustic waves can be generated by a fan instability. We present analytical estimates of the wave growth rate and ion beam heating rate. These estimates, which are confirmed by particle simulations, indicate that the perpendicular temperature of the beam ions will increase by 30 eV/s, or by 1 eV in 20–25 km. From the simulations we also conclude that the heating saturates at a perpendicular temperature around 200 eV, which is consistent with observations.     

Ionospheric signatures of magnetospheric boundaries in the post-noon sector

Spatial structures in ionospheric electron density revealed in a tomographic image have been identified with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identified by both red- and green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classified as from the boundary plasma sheet (BPS). The harder particles are identified with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary.On leave from Artic Geophysics, University Course on Svalbard (UNIS), N-9170 Longyearbyen, Norway     

我国空间物理研究进展

经过多年的建设与努力,我国日地空间物理与空间天气领域的研究呈现蓬勃的发展态势.《地球物理学报》以空间物理为专辑,集中在2014年11期刊发38篇文章,涵盖了基于"子午工程"观测数据分析在内的空间物理和空间天气方面的一批最新研究成果.这些工作涉及电离层、中高层大气、地磁与磁层、太阳及太阳风等学科方向,还有两篇工作涉及行星空间环境.本文将从这五个学科方向简要地介绍收入专辑的这些工作.     

DEMETER卫星观测到的智利7.9级地震前的电离层电磁扰动

利用法国DEMETER卫星观测的电离层电磁数据,分析了2007年11月14日智利7.9级地震前10天内的电磁信号记录,结果发现在震前1周内,低频电磁扰动开始在比较宽的纬度范围内增强,震前3天异常信号幅度达到最大,并在低纬度地区尤其突出.以5天为间隔,比较分析了多参量的空间图像,发现在震前5天异常幅度和范围扩大,震中位于异常区域的边缘地带.分析认为,这次地震前的异常信号与孕震区电磁辐射信号增多及空间加热扰动有关.     

Method of characteristics in spherical geometry applied to a Harang-discontinuity situation

The method of characteristics for obtaining spatial distributions of ionospheric electrodynamic parameters from ground-based spatial observations of the ground magnetic disturbance and the ionospheric electric field is presented in spherical geometry. The method includes tools for separation of the external magnetic disturbance, its continuation to the ionosphere, and calculation of ionospheric equivalent currents. Based on these and the measured electric field distribution, the ionospheric Hall conductance is calculated as the primary output of the method. By estimating the Hall- to-Pedersen conductance ratio distribution, the remaining ionospheric electrodynamic parameters are inferred. The method does not assume = 0 to allow to study time-dependent situations. The application of this method to a Harang discontinuity (HD) situation on 27 October 1977, 17:39 UT, reveals the following: (1) The conductances at and north of the HD are clearly reduced as compared to the eastern electrojet region. (2) Plasma flow across the HD is observed, but almost all horizontal current is diverted into upward-flowing field-aligned currents (FACs) there. (3) The FACs connected to the Hall currents form a latitudinally aligned sheet with a magnitude peak between the electrically and magnetically defined HD, where break-up arcs are often observed. Their magnitude is larger than that of the more uniformly distributed FACs connected to the Pedersen currents. They also cause the southward shift of the magnetically defined HD with respect to the electrically defined one. (4) A tilt of the HD with respect to geomagnetic latitude as proposed by an earlier study on the same event, which used composite vector plot technique, and by statistical studies, is not observed in our single time-step analysis.Also at: Finnish Meteorological Institute, Geophysical Research, P.O. Box 503, FIN-00101 Helsinki, Finland.     

Ionospheric measurements during the CRISTA/MAHRSI campaign: their implications and comparison with previous campaigns

The CRISTA/MAHRSI experiment on board a space shuttle was accompanied by a broad campaign of rocket, balloon and ground-based measurements. Supporting lower ionospheric ground-based measurements were run in Europe and Eastern Asia between 1 October–30 November, 1994. Results of comparisons with long ionospheric data series together with short-term comparisons inside the interval October-November, 1994, showed that the upper middle atmosphere (h =80–100 km) at middle latitudes of the Northern Hemisphere in the interval of the CRISTA/MAHRSI experiment (4–12 November, 1994) was very close to its expected climatological state. In other words, the average results of the experiment can be used as climatological data, at least for the given area/altitudes. The role of solar/geomagnetic and “meteorological” control of the lower ionosphere is investigated and compared with the results of MAP/WINE, MAC/SINE and DYANA campaigns. The effects of both solar/geomagnetic and global meteorological factors on the lower ionosphere are found to be weak during autumn 1994 compared to those in MAP/WINE and DYANA winters, and they are even slightly weaker than those in MAP/SINE summer. The comparison of the four campaigns suggests the following overall pattern: in winter the lower ionosphere at northern middle latitudes appears to be fairly well “meteorologically” controlled with a very weak solar influence. In summer, solar influence is somewhat stronger and dominates the weak “meteorological” influence, but the overall solar/meteorological control is weaker than in winter. In autumn we find the weakest overall solar/meteorological control, local effects evidently dominate.     

我国中低纬度地区Sq焦点的分析与研究

本文利用１９８８年３月－１９８９年３月几次大的太阳活动期间我国９个台站的地磁资料，采用无穷大平板电流的等效电流体系方法，分析了我国中低纬度地区Ｓｑ焦点位置的变化特征，并对照ＫｐＤｓｔ，Ａｐ等指数给出了Ｓｑ焦点位置变化的合理解释。结构表明：（１）在不同的Ｋｐ指数段Ｓｑ焦点有不同的规律性，当Ｋｐ＜４时，随着Ｋｐ指数增大，Ｓｑ焦点向高纬方向移动；当Ｋｐ在４和６之间时，随着Ｋｐ指数增大，Ｓｑ焦点向低纬方向     

Modification Of Sporadic E-Layers Caused By Seismic Activity

Among all earthquake precursors, those related to electromagneticeffects are the most puzzling, and the many possible sources ofnoise are cause of lively controversies. A large number oflaboratory experiments clearly suggest that micro-fracturingis associated with the appearance of spontaneous charge production(electrification) and transient Electric or ElectroMagnetic (EM)Emission. Many electric and magnetic pre-seismic and co-seismiceffects have been reported in the past as well as ionosphericperturbations. The aim of this paper is to review some of theseionospheric perturbations performed in the former Soviet Union.The importance of sporadic E-layer formation is underlined.Statistical studies with the available observations are done.At the end, a physical model of lithosphere-ionosphere couplingis presented in order to explain the observations. This modeltakes into account the following effects at the Earth's surface:electric charge generation, emanation of radioactive gas,temperature variation, and surface vibration. It is shown thatthese effects can trigger sporadic E-layer formation.     

基于探空火箭的朗缪尔探针方案设计

为研究中国低纬电离层垂直高度的精细结构,研发了一种以探空火箭为平台朗缪尔探针,用于就位测量电离层空间等离子体的特性参数及其扰动情况.本文分析了朗缪尔探针的任务需求和目标,并在朗缪尔探针基本测量原理的基础上,对朗缪尔探针基本测量方案进行了论证分析和设计,包括传感器形状、大小和表面镀层的选取设计,双探针的设计,扫描电压和工作模式的设计,及电子学测量电路的设计.本朗缪尔探针采用两路完全相同的球形探针,两路探针同步工作,各自独立完成测量.朗缪尔探针研制完成后,分别进行了信号模拟源测试和等离子体源测试:信号模拟源测试结果显示两路探针电子学工作状态良好,对微弱电流信号的响应具有很高的线性度;在等离子体模拟装置内对电子探针整机测试的初步结果表明该载荷可以正确测量等离子体的特性参数,能够满足科学探测的需求.     

Superposed epoch analysis applied to large-amplitude travelling convection vortices

For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for largeamplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients geoeffective, which have the tendency to recur with the solar rotation period.     

Simultaneous ionospheric and magnetospheric observations of azimuthally propagating transient features during substorms

During the 6^th August 1995, the CUTLASS Finland HF radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14 s. Data from such scans, during the substorm expansion phase, revealed pulses of equatorward flow exceeding 600 m s^–1 with a duration of 5 min and a repetition period of 8 min. Each pulse of enhanced equatorward flow was preceded by an interval of suppressed flow and enhanced ionospheric Hall conductance. These transient features, which propagate eastwards away from local midnight, have been interpreted as ionospheric current vortices associated with fieldaligned current pairs. The present study reveals that these ionospheric convection features appear to have an accompanying signature in the magnetosphere, comprising a dawnward perturbation and dipolarisation of the magnetic field and dawnward plasma flow, measured in the geomagnetic tail by the Geotail spacecraft, located at L = 10 and some four hours to the east, in the postmidnight sector. These signatures are suggested to be the consequence of the observation of the same field aligned currents in the magnetosphere. Their possible relationship with bursty Earthward plasma flow and magnetotail reconnection is discussed.     

中国区域电离层TEC与月均值偏差的空间相关性研究

本文利用美国喷气动力实验室(JPL)提供的电离层总电子含量(TEC)的地图网格产品,计算了中国区域上空电离层TEC与月均值偏差及其空间相关系数矩阵,从而分析了TEC与月均值偏差空间相关性的分布特征,根据统计学中定义的相关距离提取了这种偏差在经、纬度方向上的空间特征尺度.并以2008年和2011年为例,着重考察了TEC月偏差的空间特征尺度与太阳活动水平、地磁条件和季节变化之间的关系.结果发现,TEC与月均值偏差的空间相关性呈现椭圆形高斯分布的特征,沿纬线方向的特征尺度大于沿经线方向,不同纬度区域偏差的空间相关性特征差异明显,高纬的特征尺度在两个方向上均小于低纬,而不同经度区域在相同地方时条件下表现差异不大;两个方向的特征尺度在白天、太阳活动水平高和地磁活动剧烈时均存在增大的现象.     

Ionospheric index of solar activity based on the data of measurements of the spacecraft signals characteristics

The method for estimating an ionospheric index of solar-activity (IISA) based on the processing of spacecraft radio signals is suggested. The IISA values have been obtained by comparison between the measured and calculated variations of radio-signal characteristics. To calculate the variations of radio-signal characteristics, the straight rays approximation and the solar-activity index (Wolf numbers W and/or values of F_10.7 solar flux) as a control parameter of the ionospheric model have been used. The suggested method was tested using spacecraft radio signals from the radio-navigation system “CIKADA”. The reduced differences of phases (ΔΦ) for frequencies 150 and 400 MHz were measured and the same characteristics were calculated by integration along the ray of radio-wave propagation between the receiver and the satellite. The IRI-95 has been used as a background ionospheric model. The satellite co-ordinates were determined using the orbit parameters recorded in the navigation messages. Minimization of the difference measured and calculated ΔΦ using arbitrary time steps, or during whole time intervals of observation, gives the IISA corresponding the satellite pass. Daily IISA values were obtained by averaging over all communication contacts during a day (20–30 passes). Testing this approach based on the measurements during March/April 1997, 1998, shows that on magnetically quiet days differences between IISA and the primary solar activity indices are about 5%.     

Ionospheric conductance distribution and MHD wave structure: observation and model

The ionosphere influences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are different eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This effect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.     

A Review Of Slr Contributions To Geophysics In Eurasia By Cgs

In the past 30 years the Satellite Laser Ranging(SLR) technique has improved to a large extent, currently achieving a ranging precision down toa few millimeters. Moreover the growth in the size of the international network of SLR stations and therapidly growing constellation of geodetic target satellites make the SLR a well established technique for solidEarth studies and for the related Earth subsystem sciences. The long SLR observation history has become a veryimportant source of data for global and local changes detection and monitoring in many different fields.Tectonic plate motion, crustal deformation, post-glacial rebound and subsidence, Earth rotation, and polarmotion, time variations of the Earth's gravitational field, ocean tides modeling, center of mass of the totalEarth system monitoring, International Terrestrial Reference System (ITRS) maintenance are only themain applications in which the SLR technique plays a significant role. Plate boundary zones in whichdeformation is diffuse are in general geographical areas associated with high seismic and volcanic activity.A principal key to understand the geophysics of a plate boundary process is the detailed knowledge of the3-D kinematics. This work will focus on the relevant results of the Eurasian SLR subnetwork in termsof technological evolution and crustal deformation. A general overview of the Eurasian SLR stationperformance will be presented with particular reference to the state-of-the-art SLR observatory MLRO (Matera LaserRanging Observatory). The current tectonic deformations (velocity and strain-rate field) detectedby the Eurasian network and by the former WEGENER/MEDLAS campaigns will also be discussed.     

On the spectrum of mid-latitude sporadic-E irregularities

We discuss the creation of mid-latitude sporadic-E plasma irregularities (with length-scales smaller than sporadic layer thickness) by the neutral atmosphere turbulence. Using fluid equations, the relation between plasma density fluctuations and the velocity field of neutrals is derived. After a brief discussion of the relevant neutral turbulence, the analytical expression for the power spectrum of plasma irregularities is obtained. This expression allows a power-law type of experimental irregularity spectra (the spectral index depends on sporadic-E characteristics) and possible departures in detail of the irregularity spectra from the power-law form to be explained. In addition, it allows us to make estimates of length-scales at which such departures must occur.     

Latitudinal and longitudinal dispersion of energetic auroral protons

Using a collision by collision model from Lorentzen et al., the latitudinal and longitudinal dispersion of single auroral protons are calculated. The proton energies varies from 1 to 50 keV, and are released into the atmosphere at 700 km altitude. The dipole magnetic field has a dip-angle of 8 degrees. Results show that the main dispersion region is at high altitudes (300–350 km) and occurs during the first few charge exchange collisions. As the proton travels further down the atmosphere the mean free path becomes smaller, and as a result the spreading effect will not be as pronounced. This means that the first few charge exchange collisions fully determines the width of both the latitudinal and longitudinal dispersion. The volume emission rate was calculated for energies between 1 and 50 keV, and it was found that dayside auroral hydrogen emissions rates were approximately 10 times weaker than nightside emission rates. Simulations were also performed to obtain the dependence of the particle dispersion as a function of initial pitch-angle. It was found that the dispersion varies greatly with initial pitch-angle, and the results are summarized in two tables; a main and an extreme dispersion region.     

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.