基于深度学习的极光亚暴时-空自动检测

准确快速地检测极光亚暴具有重要的意义.现有利用机器学习技术自动检测亚暴起始时刻的方法无法同时兼顾检测精度和效率.本文基于深度学习技术提出了一个端到端的亚暴起始检测模型,该模型利用双流卷积网络提取亚暴的时-空特征,并用三个一维时序卷积层获得亚暴起始的概率序列.该模型在Polar卫星1996-1998年极光观测上获得了87...     

Features of the planetary distribution of auroral precipitation characteristics during substorms

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.     

Auroral intensification structure and dynamics in the double oval: Substorm of December 26, 2000

Based on results of the simultaneous TV observations at Barentsburg high-latitude observatory and Lovozero auroral observatory and using the IMAGE auroral luminosity images, the auroral fine structure and dynamics has been studied during the substorm of December 26, 2000, when the auroral luminosity distribution represented a double oval. It has been indicated that the interaction between the processes proceeding in different magnetospheric regions, the projections of which are the poleward and equatorward edges of the double oval, is observed in auroras in the process of substorm development.     

Relation of auroral substorm onset to local AL index and dispersionless particle injections

In this study, we investigate the relation of auroral substorm onset to the sharp decrease in the local AL index (IL) during substorms. With a database of over 4200 onsets determined from auroral images, we have statistically examined the timing between the auroral substorm onset and the sharp decrease in the IL index, as determined with data from the IMAGE magnetometer network. From the database of onsets, 54 substorms were determined to be within 6° of the central meridian of the IMAGE ground array. Our superposed epoch median curve shows that the IL index begins to sharply decrease 3 min before the auroral onset, which is twice the 2 min resolution of the auroral imager. However, the mean difference determined by measuring the time between the start of the IL decrease and the auroral substorm onset is about 1.1±0.6 min. An analysis of the superposed epoch median curves of the SOPA particle data for the LANL spacecraft closest to the auroral onset meridian indicates that both the electron and proton injections begin about 3 min before the auroral onset. However, the mean time of the difference between the minimum of the particle dispersionless injection and the auroral onset is simultaneous within the uncertainty of the auroral onset and the error of the mean for the injection. The location of the electron injection relative to the IMAGE ground array seems to be 01–04 MLT, while the proton injection appears to be in the 22–01 MLT sector. These statistical results support the idea that the field aligned and ionospheric currents of the substorm current wedge begin to flow before the auroral onset.     

一种基于紫外极光图像的亚暴膨胀期起始时刻的自动检测方法

准确界定亚暴起始时刻是理解亚暴相关问题的关键.已有研究主要集中在两方面:一是从极光图像中人工挑选亚暴事件进行案例分析或统计分析来研究亚暴发生机制及亚暴期间的地磁环境;二是基于一些空间物理参数,如AE指数、SME(SuperMAG electrojet)指数、Pi2、正弯扰等,采用人眼判断或是模式识别的方法从中找出亚暴起始时刻.本文尝试采用模式识别的方法从紫外极光图像中自动地检测出亚暴膨胀期起始时刻.首先,将紫外极光图像通过网格化处理转换到磁地方时-地磁纬度(MLT-MLAT)直角坐标下,然后通过模糊c均值聚类方法提取亮斑,再考察亮斑强度是否增强、面积是否极向膨胀来判断是不是亚暴事件.本文方法在1996年12月-1997年2月这三个月的Polar卫星紫外极光图像上进行了实验验证.我们将检测到的亚暴起始时刻与Liou(J. Geophys. Res., 2010, 115: A12219)的人工标记进行了对比,并详细分析了与标记不一致的多检和漏检事件.本文提出的自动检测方法可以快速地从海量紫外极光图像中完成亚暴事件的初步筛选,方便研究人员进一步深入研究极光亚暴.     

Injection of relativistic electrons into the internal magnetosphere during magnetic storms: Connection with substorms

The connection between rapid increases in the intensity of electrons with energies >0.3 MeV and magnetospheric substorms was studied for the first time by measurements of energetic electrons on the low-orbit SERVIS-1 satellite. In addition to the well-known process of radial diffusion detected at the recovery phase, the increases during a period of time no longer than 1.5 h at the main phase of six magnetic storms in a channel of 0.3–1.7 MeV (in three of them, in a channel of 1.7–3.4 MeV) were measured. An analysis of auroral zone magnetograms demonstrated that the increases occurred at the instant of magnetospheric substorm activation. A conclusion is made that the increases are caused by the radial injection of electrons by a pulse electric field induced during substorm activations. Pulse injections are shown to be one of the main mechanisms of electron radiation belt completion in the inner magnetosphere and, in combination with moderate radial diffusion, to be responsible for the appearance of large fluxes of energetic electrons (“killers”) in the magnetosphere after magnetic storms.     

Multiscale phenomena in the near-Earth magnetosphere

Several studies on the scaling properties of the near-Earth magnetosphere and auroral phenomena are reviewed. These studies employ modern analysis techniques that include fractal, multifractal, wavelet, wavelet bicoherence, and sign-singularity analyses as well as cellular automaton simulations of sandpile and avalanches. The results provide strong evidence for the multiscale, cross-scale coupling, and reorganization nature of auroral and magnetospheric phenomena, suggesting the possibility that the magnetosphere is in a forced and/or self organized critical state. Signatures of inverse cascade are found in magnetic fluctuations in current disruption events, which may indicate large-scale substorm features such as substorm current wedge and plasmoid may be evolved from small-scale plasma turbulence structures. Insights gained from these studies help to discriminate the existing competing substorm models. The multiscale properties of magnetospheric substorms are consistent with substorm models with intrinsic multiscale processes and not with substorm models with only a macroscopic process.     

Spatial-temporal dynamics of auroras during the magnetic storm main phase

The structure and dynamics of auroras in the midnight sector during substorms, which develop during the magnetic storm main phase as compared to the characteristics of a typical auroral substorm, have been studied using the ground-based and satellite observations. It has been found out that a difference from the classical substorm is observed in auroras during the magnetic storm main phase. At the beginning of the storm main phase, the series of pseudobreakups with the most pronounced jump-like motion toward the equator shifts to lower latitudes. The substorm expansion phase can be observed not only as arc jumps to higher latitudes but also as an explosive expansion of a bright diffuse luminosity in all directions. During the magnetic storm main phase, auroras are mainly characterized by the presence of stable extensive rayed structures and by the simultaneous existence of different auroral forms, typical of different substorm phases, in the TV camera field of view.     

Planetary features of aurorae: Results of the IGY (a review)

In the period of the International Geophysical Year (IGY), almost the entire planet was covered for the first time by ground-based geophysical observations. Their analysis led to two fundamental results: the existence of the auroral oval and auroral (magnetospheric) substorm. At the final stage of the IGY, satellite explorations of the near-Earth space began. The auroral luminosity appeared to be related to the plasma structure of the magnetosphere. That opened new possibilities for parameters diagnostics of the Earth’s magnetosphere on the basis of ground-based aurora observations. The concepts of auroral oval and magnetospheric substorm became paradigms of the new science of solar-terrestrial physics.     

Auroral fading structure before breakup: A review

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.     

极光亚暴期间的南极中山站地磁共轭点位置研究

通过对北极斯瓦尔巴特( Svalbard )岛Longyearbyen台站的 极光扫描光度计和地磁 观测数据在地磁亚暴膨胀相期间的对比分析,发现扫描光度计记录中的极光边缘的快速极向 运动和地磁数据x分量的陡峭负弯之间有着良好的对应关系,地磁数据可用来研究两极 高纬 地区极光亚暴的地磁共轭特征. 对南极中山站、挪威Troms Svalbard台链和东格陵兰岛 地 区共15个地磁台站在7个典型极光亚暴事件中的地磁数据进行对比分析后发现, 中山站的地 磁共轭点位置存在明显的漂移特征,漂移的范围在斯瓦尔巴特岛与东格陵兰岛之间,纬度值 与CGM模型值近似.     

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic field, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its first few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s^-1 poleward, finally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at ~6 km s^-1, whilst the eastward edge also expands eastward at ~0.6 km s^-1. Typical flows of 600 m s^-1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to ~100 m s^-1 and 10–20 S respectively at activation. The initial flow response to the substorm expansion phase onset is a flow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the flow, resulting in a region of low-electric field, but also low conductivity poleward of the high-conductivity region. Rapid flows are observed at the edge of the high-conductivity region, and subsequently the high flow region develops, flowing around the expanding auroral feature in a direction determined by the flow pattern prevailing before the substorm intensification. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2° further poleward than the UV auroral signature associated with it.     

TC-1卫星在近地磁尾观测到的持续尾向流、等离子体片变薄和偶极化过程

2004年7月14日TC-1卫星在近地磁尾(-9.3Re,-5.4Re,1.2Re)附近观测到了伴随有持续尾向流的等离体片变薄和偶极化过程.尾向流持续时间为32分钟.偶极化过程中磁场By分量没有明显变化.在偶极化过程发生两分钟之后,地面台站观测到的Pi2脉动.ACE卫星的观测表明行星际磁场有弱的南向行星际磁场（-2nT）,持续时间约55分钟.Imagine卫星在电离层区域没有观测到极光出现.和伴随有极光增亮的亚暴过程相比,南向行星际磁场明显较弱,且持续时间短.TC-1卫星和ACE卫星的联合观测表明尾部释能有大有小,并非达到某值才能发生.但能量小时,不能够引起极光亚暴.其次南向行星际磁场有可能与近地磁尾尾向流有密切关系.     

Substorm correlated absorption on a 3200 km trans-auroral HF propagation path

A high-frequency transmitter located at Clyde River, NWT, Canada, and a receiver located near Boston, USA, provide a 3200 km trans-auroral, near-meridional propagation path over which the propagation characteristics have been measured. Out of the fourteen frequencies in the HF band sampled every hour for the duration of the experimental campaign (16 January-8 February 1989), the signal level measurements of 6.800 MHz transmissions were selected in order to determine the extent and occurrence of auroral absorption. The median level of auroral absorption along the path is found to increase with geomagnetic activity, quantified by the index K_p, with the increase being greater in the post-midnight sector than in the pre-midnight sector. This asymmetric behaviour is attributed to the precipitation of high energy electrons into the midnight and morning sector auroral D region. The measured diurnal variation in the median level of absorption is consistent with previous models describing the extent and magnitude of auroral absorption and electron precipitation. Individual substorms, identified from geosynchronous satellite data, are found to cause short-lived absorption events in the HF signal level of \sim30 dB at 6.800 MHz. The occurrence of substorm correlated auroral absorption events is confined to the midnight and morning sectors, consistent with the location of the electron precipitation. The magnitude of absorption is related to the magnetotail stress during the substorm growth phase and the magnetotail relaxation during the substorm expansion phase onset. The absorption magnitude and the occurrence of substorms during the period of the campaign increase at times of high K_p, leading to an increase in median auroral absorption during disturbed periods.     

The convection electrojet and the substorm electrojet

Enhancements in the auroral electrojets associated with magnetospheric substorms result from those in either the electric field or the ionospheric conductivities, or both. Their relative importance varies significantly, even during a single substorm, depending on the location as well as on the substorm phases. It is predicted that different parts of the electrojets tend to respond in different ways to substorm activity. The unprecedented, unique opportunity for CLUSTER spacecraft observations of electric/magnetic fields and precipitating particles, combined with radar measurements of ionospheric quantities and with ground magnetometers, will provide us with crucial information regarding the physical nature of the separation between the “electric field-dominant” and “conductivity-dominant” auroral electrojets. This study also discusses the implications of these two auroral-electrojet components in terms of solar wind-magnetosphere-ionosphere interactions.     

亚暴期间高纬黄昏-子夜扇区极光弧增亮与衰减及其与IMF的关系

利用南极中山站极光全天空摄相、地磁、地磁脉动数据和Wind卫星的行星际磁场IMF观测数据，分析了7个亚暴期间高纬黄昏-子夜扇区极光弧的短暂增亮现象.极光弧特征是，短暂增亮随后很快衰减，历时10-20min，基本沿着日-地方向，有明显黄昏方向运动.这些事件大都发生在IMFB_z南转之后，亚暴增长相或膨胀相期间，极光浪涌到达之前10-73min消失.相应的IMFB_x＞0，IMFB_y＜0.这种极光弧和亚暴极光不同，它们与地磁活动及Pi2脉动不相关.这7个极光弧的形态和IMF特征表明，极光弧的增亮很可能由尾瓣重联产生，很快衰减归因于IMFB_z南向条件，而黄昏方向运动受IMFB_y控制.     

A multipoint study of a substorm occurring on 7 December, 1992, and its theoretical implications

On 7 December 1992, a moderate substorm was observed by a variety of satellites and ground-based instruments. Ionospheric flows were monitored near dusk by the Goose Bay HF radar and near midnight by the EISCAT radar. The observed flows are compared here with magnetometer observations by the IMAGE array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF B_z component. The data presented show that the substorm onset electrojet at midnight was confined to closed field lines equatorward of the pre-existing convection reversal boundaries observed in the dusk and midnight regions. No evidence of substantial closure of open flux was detected following this substorm onset. Indeed the convection reversal boundary on the duskside continued to expand equatorward after onset due to the continued presence of strong southward IMF, such that growth and expansion phase features were simultaneously present. Clear indications of closure of open flux were not observed until a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven by reconnection in the tail.     

Westward moving dynamic substorm features observed with the IMAGE magnetometer network and other ground-based instruments

We present the ground signatures of dynamic substorm features with particular emphasis on the event interpretation capabilities provided by the IMAGE magnetometer network. This array covers the high latitudes from the sub-auroral to the cusp/cleft region. An isolated substorm on 11 Oct. 1993 during the late evening hours exhibited many of well-known features such as the Harang discontinuity, westward travelling surge and poleward leap, but also discrete auroral forms, known as auroral streamers, appeared propagating westward along the centre of the electrojet. Besides the magnetic field measurements, there were auroral observations and plasma flow and conductivity measurements obtained by EISCAT. The data of all three sets of instruments are consistent with the notion of upward field-aligned currents associated with the moving auroral patches. A detailed analysis of the electro-dynamic parameters in the ionosphere, however, reveals that they do not agree with the expectations resulting from commonly used simplifying approximations. For example, the westward moving auroral streamers which are associated with field-aligned current filaments, are not collocated with the centres of equivalent current vortices. Furthermore, there is a clear discrepancy between the measured plasma flow direction and the obtained equivalent current direction. All this suggests that steep conductivity gradients are associated with the transient auroral forms. Also self-induction effects in the ionosphere may play a role for the orientation of the plasma flows. This study stresses the importance of multi-instrument observation for a reliable interpretation of dynamic auroral processes.     

CRRES/Ground-based multi-instrument observations of an interval of substorm activity

Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L=7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.