共查询到20条相似文献，搜索用时 31 毫秒
1.
Y. I. Feldstein 《Geomagnetism and Aeronomy》2016,56(2):129-142
The auroral oval concept radically changed the view that existed for a century in geophysics on the patterns in aurora planetary spatial–temporal distributions. The auroral zone, which is located around the geomagnetic pole as a continuous ring at a constant angular distance of ~23°, was replaced by the auroral oval in 1960. The auroral oval spatial position reflects the shape of the Earth’s magnetosphere, which is compressed by the solar wind on the dayside and stretches into the magnetotail on the nightside. The oval is fixed relative to the direction toward the Sun and is located around the geomagnetic pole at altitudes of the upper atmosphere at an angular distance of ~12° at noon and ~23° at midnight. After an animated discussion over several subsequent years, the existence of the auroral oval was accepted by the scientific community as a paradigm of a new science, i.e., solar–terrestrial physics. The oval location indicates the zone where electron fluxes with energies varying from ~100 eV to ~20 keV precipitate into the upper atmosphere and is related to the structure of plasma domains in the Earth’s magnetosphere. The paper describes the scientific studies that resulted in the concept of the auroral oval existence. It has been shown how this concept was subsequently justified in the publications by Y.I. Feldstein and O.B. Khorosheva. The issue of the priority of the auroral oval concept introduction into geophysics has been considered. The statement that the concept of the oval is an archaic paradigm of solar–terrestrial physics has been called into question. Some scientific fields in which the term auroral oval or simply oval was and is the paradigm have been listed. 相似文献
2.
Joachim Vogt 《Surveys in Geophysics》2002,23(4):335-377
Auroral phenomena are controlled by the geomagnetic field.Since the terrestrial field lines connect the auroral oval to the equatorial region at large distances, the collisionless plasma in this remote space environment can act as a power supply for the high-latitude upper atmosphere where auroral emissions take place. The coupling process is intimately linked to currents which flow across the local magnetic field direction both in the equatorial part and at the atmospheric end of the auroral field lines. These two auroral key regions are connected through currents flowing along the terrestrial field lines, thereby completing the auroral current circuit. Such field-aligned currents are carried by Alfvén waves, that is, magnetohydrodynamic shear waves, which are thus a means to exchange momentum and energybetween rather remote parts of the geomagnetically controlledspace environment. Auroral dynamics is further affected by a third key region in the auroral current circuit, namely the auroral acceleration region, where parallel electric fields accelerate particle to keV energies. This review focuses on key region coupling through Alfvén waves. Continuity requirements for currents and electric fields provide a convenient means to describe the interaction of Alfvén waves with different plasma regimes. Basic coupling aspects can be demonstrated with the help of a simplified model. Inhomogeneities and nonlinear feedback can lead to resonance effects and instabilities. 相似文献
3.
N. I. Izhovkina 《Geomagnetism and Aeronomy》2011,51(3):342-347
The density and temperature of the plasma electron component and wave emission intensity in the topside ionosphere were measured
by the INTERCOSMOS-19 satellite. In the subauroral ionosphere, a decrease in the plasma density correlates with an increase
in the plasma electron component temperature. In this case, the additional increase in the electron component temperature
was measured in regions with increased plasma density gradients during the substorm recovery phase. In a linear approximation,
the electromagnetic wave growth increments are small on electron fluxes precipitating in the auroral zone. It has been indicated
that Bernstein electromagnetic waves propagating in the subauroral topside ionosphere can intensify in regions with increased
plasma density gradients on electron fluxes orthogonal to the geomagnetic field, which are formed when plasma is heated by
decaying electrostatic oscillations of the plasma electron component. This can be one of the most important factors responsible
for the intensification of auroral kilometric radiation. 相似文献
4.
D. A. Lorentzen 《Annales Geophysicae》1999,18(1):81-89
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. 相似文献
5.
通过观测资料的分析和数值模拟，研究了热带大气季节内振荡与ＥＮＳＯ的相互关系．一方面，在Ｅ１Ｎｉｎｏ事件发生之前，热带大气季节内振荡（尤其是在赤道中西太平洋地区）异常偏强，通过海一气相互作用它可能是Ｅ１Ｎｉｎｏ的一种重要激发机制．同时，赤道中西太平洋地区大气季节内振荡的异常加强同东亚中高纬度地区３０-６０天振荡的加强和强东亚冬季风有关．另一方面，ＥＮＳＯ对热带大气季节内振荡也有重要影响，在Ｅ１Ｎｉｎｏ期间，热带大气季节内振荡明显减弱；其结构明显趋于正压性． 相似文献
6.
V. G. Vorobjev O. I. Yagodkina G. V. Starkov Ya. I. Feldstein 《Geomagnetism and Aeronomy》2007,47(2):193-204
A planetary pattern of substorm development in auroral precipitation has been constructed on the basis of the F6 and F7 satellite observations. The behavior of the auroral injection boundaries and characteristics of precipitating electrons in various precipitation regions during all phases of a statistically mean magnetospheric substorm with an intensity of AL ～ ?400 nT at a maximum is considered in detail. It is shown that during a substorm, the zone of structured auroral oval precipitation AOP and the diffuse auroral zone DAZ are the widest in the nighttime and daytime sectors, respectively. In the daytime sector, all precipitation regions synchronously shift equatorward not only at the origination phase but during the substorm development phase. The strongest shift to low latitudes of the daytime AOP region is observed at a maximum of the development phase. As a result of this shift, the area of the polar cap increases during the phases of substorm origination and development. It is shown that the average position of the precipitation boundaries and the energy fluxes of precipitating electrons at each phase are linearly related to the intensity of a magnetic disturbance. This makes it possible to develop a model of auroral precipitation development during each phase of substorms of any intensity. 相似文献
7.
面对日积月累产生的海量极光数据,快速发现极光现象的发生及活动特征是研究极光的物理机制及相关动力学过程的首要问题,它为研究极光现象提供有效的自动化分析手段,从而能够提供充足而有效的事件用于统计学分析.因为太阳风是等离子体,它有着磁流体力学的特征,本文采用流体力学的连续性方程对极光运动进行建模,提取全天空极光图像序列的运动场,对极光活动进行表征,进而构造极光活动变化曲线,从而有效的检测出极光活动的变化.该方法的优势在于,基于运动场的表征方法能够有效反映极光活动的二维形态和运动特征,生成的极光活动变化曲线可以准确地指示极光发生、变化和消失的时间,为进一步研究极光的活动周期及相关物理变化奠定基础. 相似文献
8.
N. V. Isaev V. M. Kostin G. G. Belyaev O. Ya. Ovcharenko E. P. Trushkina 《Geomagnetism and Aeronomy》2010,50(2):243-255
The measurements on board the Cosmos-1809 satellite of various parameters of the topside ionosphere plasma during more than
ten typhoons in various regions are analyzed. It is shown that specific zones of increased pressure of the electron gas, electric
field, and intense ion oscillations are formed during the intensification stage. In some cases the “typhoon eye” is formed
over the tropical depression zone in the ionosphere, that is, the region with sharply decreased plasma density and pressure
is observed a day and more prior to the moment when it happens in the atmosphere. 相似文献
9.
This review is devoted to auroral fading before beginning of the substorm active phase. This initial stage of the active phase called breakup is accompanied by a sharp brightening of auroras and their rush toward the pole. Auroral fading before breakup was first detected in discrete auroras in the nightside sector and consisted in that a short-term decrease in brightness of an arc moving toward the equator below the level observed during the preliminary phase was observed during the substorm preliminary phase 2–3 min before breakup. During fading, the velocity of equatorward motion of auroral arcs decreased up to their complete stoppage. Auroral fading in the noon sector was registered simultaneously with fading on the Earth’s nightside before the beginning of the active phase. Short-term background fading was also observed both equatorward and poleward of an arc on the nightside. It was subsequently indicated that similar fading is observed in various geophysical phenomena. It was detected that a radar aurora signal fades before breakup, if auroral substorm is observed in a radar pattern and substorm source is located under good aspect conditions. Riometer absorption decreases simultaneously with auroral fading. Geomagnetic pulsations decay on dayside and nightside immediately before breakup. Such a multiform manifestation of fading in various geophysical phenomena indicates that fading is related to some global processes proceeding in the magnetosphere when energy accumulation in this region comes to the end before its explosive release into the polar ionosphere. 相似文献
10.
K. Mohanakumar 《Annales Geophysicae》1994,12(5):448-456
A study on the variability of temperature in the tropical middle atmosphere over Thumba (8 32’ N, 76 52’ E), located at the southern part of India, has been carried out based on rocket observations for a period of 20 years, extending from 1970 to 1990. The rocketsonde-derived mean temperatures over Thumba are corrected prior to 1978 and then compared with the middle atmospheric reference model developed from satellite observations and Solar Mesosphere Explorer (SME) satellite data. Temperature variability at every 1 km interval in the 25–75 km region was analysed. The tropical stratosphere is found to be highly stable, whereas considerable variability is noted in the middle mesosphere. The effect of seasonal cycle is least in the lower stratosphere. Annual and semi-annual oscillations in temperature are the primary oscillations in the tropical middle atmosphere. Annual temperature oscillations are dominant in the mesosphere and semi-annual oscillations are strong in the stratosphere. The stratopause region is noted to be the part of the middle atmosphere least sensitive to the changes in solar activity and long-term variability. 相似文献
11.
The geomagnetic observations, performed at the global network of ground-based observatories during the recovery phase of the superstrong magnetic storm of July 15–17, 2000 (Bastille Day Event, Dst = ?301 nT), have been analyzed. It has been indicated that magnetic activity did not cease at the beginning of the storm recovery phase but abruptly shifted to polar latitudes. Polar cap substorms were accompanied by the development of intense geomagnetic pulsations in the morning sector of auroral latitudes. In this case oscillations at frequencies of 1–2 and 3–4 mHz were observed at geomagnetic latitudes higher and lower than ～62°, respectively. It has been detected that the spectra of variations in the solar wind dynamic pressure and the amplitude spectra of geomagnetic pulsations on the Earth’s surface were similar. Wave activity unexpectedly appeared in the evening sector of auroral latitudes after the development of near-midnight polar substorms. It has been established that the generation of Pc5 pulsations (in this case at frequencies of 3–4 mHz) was spatially asymmetric about noon during the late stage of the recovery phase of the discussed storm as took place during the recovery phase of the superstrong storms of October and November 2003. Intense oscillations were generated in the morning sector at the auroral latitudes and in the postnoon sector at the subauroral and middle latitudes. The cause of such an asymmetry, typical of the recovery phase of superstrong magnetic storms, remains unknown. 相似文献
12.
13.
《Journal of Atmospheric and Solar》2007,69(16):2058-2070
High-resolution observations by the FAST and Freja satellites indicate that multiscale transverse structures in magnetic-field-aligned flows are common features in the auroral ionosphere. A number of multiscale processes, such as broadband low-frequency oscillations, coherent structures, and various cross-field transport effects are well correlated with these inhomogeneities. Previously, these effects were studied using the three-dimensional multifluid model with a uniform magnetic field. In the present study a more realistic model with a dipole magnetic field has been used. Self-consistent generation of the low-frequency modes driven by local transverse gradients in the field-aligned ion flow and associated transport processes have been simulated. In spite of the large variations of the magnetic field with altitude (by several orders of magnitude), the most important features, observed in the previous simulations with a uniform magnetic field, have been reproduced with a new model. For typical polar wind conditions, it has been found that inhomogeneous parallel flow can excite low-frequency oscillations with comparable amplitudes over a wide range of altitudes (several . This leads to a significant cross-field transport over the same range of altitudes. It has also been shown that even small-amplitude short-scale modulations of the original large-scale flow profile significantly increases low-frequency mode generation and associated cross-field transport at various altitudes. The relevance of the obtained results to recent observations is discussed. 相似文献
14.
O. Luízar M. V. Stepanova J. M. Bosqued E. E. Antonova R. A. Kovrazhkin 《Annales Geophysicae》2000,18(11):1399-1411
Multiple inverted-V structures are commonly observed on the same auroral zone crossing by a lowaltitude orbiting satellite. Such structures appear grouped and apparently result from an ionospheric and/or magnetospheric mechanism of stratification. More than two years of AUREOL-3 satellite observations were analyzed to study their properties and their formation in the framework of the ionosphere-magnetosphere coupling model proposed by Tverskoy. This model predicts some natural periodicity in the electrostatic potential profile (and subsequently in the field-aligned current profiles) that could account for oscillations experimentally observed in the auroral zone, such as successive inverted-Vs. Experimental results obtained during quiet or moderately active periods demonstrate that the number of structures observed within a given event is well described by a scaling parameter provided by the hot plasma stratification theory and expressed in terms of the field-aligned current density, the total width of the current band, the plasma sheet ion temperature, and the height-integrated Pedersen conductivity of the ionosphere. The latitudinal width, in the order of 100/200 km at ionospheric altitudes, is relatively independent of the current density, and is determined not only by the existence of a potential difference above the inverted-Vs, but also by basic oscillations of the ionosphere-magnetosphere coupling system predicted by Tverskoy. The large number of cases studied by the AUREOL-3 satellite provides reliable statistical trends which permits the validation of the model and the inference that the multiple structures currently observed can be related directly to oscillations of the magnetospheric potential (or the pressure gradients) on a scale of 1000/2000 km in the near-Earth plasma sheet. These oscillations arise in the Tverskoy model and may naturally result when the initial pressure gradients needed to generate a large-scale field-aligned current have a sufficiently wide equatorial scale, of about 1 RE or more. 相似文献
15.
V. I. Badin 《Geomagnetism and Aeronomy》2011,51(2):178-186
A method for detecting discrete equidistant spectra in high-latitude magnetic observations is proposed. The method finds approximate
solutions of the classical Schuster problem, which finds a hidden periodicity in observations with considerable noise. The
usage of difference signals makes it possible to increase the latitudinal resolution of the magnetometric diagnostics. The
equidistant spectra of two different types have been detected based on the proposed method. The spectra of the first type
are interpreted as frequencies of coupled compressional-transverse magnetohydrodyncompressionalamic oscillations in the magnetospheric
cavity. The origin of the second type of spectra can be related to a rotating source, i.e., a small-scale vortex of magnetospheric
convection. Such an interpretation takes into consideration the Doppler frequency shift caused by entrainment of the ionospheric
neutral gas by magnetospheric convection. The results confirm the conclusion that discrete auroral frequencies are stable
under disturbed conditions. 相似文献
16.
根据解析求解引导中心近似的动力学方程得到的离子分布函数 ,研究了不同Kp指数条件下起源于不同电离层区域的上行O+离子通量密度沿不同经度处的磁力线的定态分布 ,并研究了上行O+离子向不同磁层区域传输的特性 .主要结果为 :（ 1 ）起源于向阳面极光带外侧及更低纬区的电离层离子基本上传输到向阳面磁层区 ;起源于背阳面极光带及更低纬区的电离层离子基本上传输到背阳面磁尾等离子体片区和闭合磁力线区 ;起源于极盖区及向阳面极光带内侧的电离层离子基本上传输到等离子体幔区和磁瓣区 .（ 2 ）上行离子主要分布在近地空间 ,其通量密度相对于地心距离呈负梯度 .（ 3）地磁活动指数Kp 增高时上行离子进入磁层的概率增大 ,因而上行离子起动力学作用的地球空间范围增大 .所得结果可解释有关地顶的观测特征 ,理论估算的上行离子在磁尾的通量密度与观测结果相符合. 相似文献
17.
Incoherent scatter radars are designed to detect scatter from thermalfluctuations in the ionosphere. These fluctuations contain, among other things,features associated with ion-acoustic waves driven by random motions within theplasma. The resulting spectra are generally broad and noisy, but neverthelessthe technique can, through a detailed analysis of spectra, be used to measure arange of physical parameters in the Earth's upper atmosphere, and provides apowerful diagnostic in studies of magnetosphere-ionosphere coupling,thermosphere dynamics and the geospace environment in general. In recent yearsthere has been much interest in naturally occurring (as opposed to artificiallystimulated) enhanced ion-acoustic spectra seen in the auroral zone andcusp/cleft region. A study of the plasma instability processes that lead tosuch spectra will help us to better understand auroral particle acceleration,wave-particle and wave-wave interactions in the ionosphere, and theirassociation with magnetospheric processes. There is now a substantial body ofliterature documenting observations of enhanced ion-acoustic spectra, but thereremains controversy over generation mechanisms. We present a review ofliterature documenting observations of naturally enhanced ion-acoustic spectra,observed mainly along the geomagnetic field direction, along with a discussionof the theories put forward to explain such phenomena. 相似文献
18.
B. G. Shpynev A. V. Oinats V. P. Lebedev M. A. Chernigovskaya I. I. Orlov A. Yu. Belinskaya O. M. Grekhov 《Geomagnetism and Aeronomy》2014,54(4):500-512
Long-term variations in the parameters of the Earth’s upper atmosphere and geophysical activity have been studied based on the current spectra. The main sources of quasiperiodic oscillations in the atmosphere (including variations in the solar radiation, geomagnetic activity, and gravity) have been considered. It was shown that the most stable quasiharmonic variations are related to tidal gravitational oscillations and Rossby planetary waves with stable spectra. These oscillatory processes substantially contribute to the dynamics of the middle and upper atmosphere and manifest themselves in ionospheric parameters. 相似文献
19.
P.-L. Blelly J. Lilensten A. Robineau J. Fontanari D. Alcaydé 《Annales Geophysicae》1997,14(12):1375-1390
A set of EISCAT UHF and VHP observations is used for calibrating a coupled fluid-kinetic model of the ionosphere. The data gathered in the period 1200–2400 UT on 24 March 1995 had various intervals of interest for such a calibration. The magnetospheric activity was very low during the afternoon, allowing for a proper examination of a case of quiet ionospheric conditions. The radars entered the auroral oval just after 1900 UT: a series of dynamic events probably associated with rapidly moving auroral arcs was observed until after 2200 UT. No attempts were made to model the dynamical behaviour during the 1900–2200 UT period. In contrast, the period 2200–2400 UT was characterised by quite steady precipitation: this latter period was then chosen for calibrating the model during precipitation events. The adjustment of the model on the four primary parameters observed by the radars (namely the electron concentration and temperature and the ion temperature and velocity) needed external inputs (solar fluxes and magnetic activity index) and the adjustments of a neutral atmospheric model in order to reach a good agreement. It is shown that for the quiet ionosphere, only slight adjustments of the neutral atmosphere models are needed. In contrast, adjusting the observations during the precipitation event requires strong departures from the model, both for the atomic oxygen and hydrogen. However, it is argued that this could well be the result of inadequately representing the vibrational states of N2 during precipitation events, and that these factors have to be considered only as ad hoc corrections. 相似文献
20.
Alv Egeland 《Journal of Atmospheric and Solar》2009,71(17-18):1749-1755
More than one hundred years ago Kristian Birkeland (1867–1917) first addressed the question as to why auroras appear overhead when the Earth's magnetic field is disturbed. He laid foundations for our current understanding of geomagnetism and polar auroras. For the first time cosmic phenomena were scaled and simulated in a laboratory. Birkeland's terrella experiments were ingenious. Even though the famous Lord Kelvin, in 1892, wrote that no matter passes between the Sun and the Earth, Birkeland's first auroral theory from 1896 is based on charged particle of solar origin, illustrated by the following quotation: “the auroras are formed by corpuscular rays drawn in from space, and coming from the sun”. Thus, the year 1896 marks the founding of space plasma physics. His most enduring contribution to auroral physics was his recognition that field-aligned currents are needed to couple auroral phenomena in the upper atmosphere to interplanetary space. The existence of field-aligned currents was controversial and disputed vigorously among scientists for more than 50 years. During The Birkeland Symposium in 1967 it was unanimously proposed that field-aligned currents in space should be called “Birkeland currents”, which was accepted by the International Union for Geomagnetism and Aeronomy. Today, plasma physicists strongly believe that many significant cosmic phenomena result from streams of Birkeland currents. 相似文献