A satellite study of dayside auroral conjugacy

A study of dayside auroral conjugacy has been done using the cleft/boundary layer auroral particle boundaries observed by the DMSP-F7 satellite in the southern hemisphere and the global UV auroral images taken by the Viking spacecraft in the northern hemisphere. The 22 events have been studied on the basis of an internal IGRF 1985 magnetic field; it is shown that there is a displacement of up to 4^° in latitude from the conjugate points with the northern aurora appearing to be located poleward of the conjugate point. No local time dependence of the north-south auroral location difference was seen. The use of a more realistic magnetic field model for tracing field lines which incorporates the dipole tilt angle and Kp index, the Tsyganenko 1987 long model plus the IGRF 1985 internal magnetic field model, appears to organize the data better. Although with this external plus internal model some tracings did not close in the opposite hemisphere, 70% of those that did indicated satisfactory conjugacy. The study shows that the degree of auroral conjugacy is dependent upon the accuracy of the magnetic field model used to trace to the conjugate point, especially in the dayside region where the field lines can either go to the dayside magnetopause near the subsolar point or sweep all the way back to the flanks of the magnetotail. Also the discrepancy in the latitude of northern and southern aurora can be partially explained by the displacement of the neutral sheet (source region of the aurora) by the dipole tilt effect.     

地基观测的夜侧极光对行星际激波的响应

行星际激波与地球磁层相互作用通常会导致日侧极光活动增强,随后沿着极光卵的晨昏两侧向夜侧扩展的激波极光.行星际激波也可能直接导致夜侧扇区极光活动增强,甚至沉降粒子能通量的数量级可以与典型亚暴相比拟.本文首次利用我国南极中山站和北极黄河站连续多年积累的极光观测数据,对行星际激波与地球磁层相互作用期间地面台站在夜侧扇区(18—06MLT)观测的极光响应进行了分析.对18个极光观测事件的分析结果表明:行星际激波与磁层相互作用可以在夜侧触发极光爆发和极光微弱增强或静态无变化事件;太阳风-磁层能量耦合的效率以及磁层空间的稳定性决定着行星际激波能否触发极光爆发.     

Interplanetary magnetic field By control of dayside auroras

The effect of the interplanetary magnetic field (IMF) By component on the dayside auroral oval from Viking UV measurements for March–November 1986 is studied. Observations of dayside auroras from Viking UV images for large positive (15 cases) and negative (22 cases) IMF By (∣By∣>4 nT), suggest that: (1) the intensity of dayside auroras tends to increase for negative IMF By and to decrease for positive By, so that negative IMF By conditions seem preferable for observations of dayside auroras; (2) for negative IMF By, the auroral oval tends to be narrow and continuous throughout the noon meridian without any noon gap or any strong undulation in the auroral distribution. For positive IMF By, a sharp decrease and spreading of auroral activity is frequently observed in the post-noon sector, a strong undulation in the poleward boundary of the auroral oval around noon, and the formation of auroral forms poleward of the oval; and (3) the observed features of dayside auroras are in reasonable agreement with the expected distribution of upward field-aligned currents associated with the IMF By in the noon sector.     

Synoptic distribution of dayside aurora: Multiple-wavelength all-sky observation at Yellow River Station in Ny-Ålesund,Svalbard

Observations acquired from three-wavelength (427.8, 557.7 and 630.0 nm) all-sky imagers (ASIs) at Yellow River Station (YRS) in Ny-Ålesund, Svalbard, are used to examine the synoptic distribution of dayside aurora. The results demonstrate that the maximum emission regions (MERs) at each wavelength are all located in the postnoon sector, but have rather different magnetic local time (MLT) distributions from each other. The so-called 15 MLT “hot spot” is the overlapping region of the MERs at three wavelengths, and the prenoon “warm spot” is characterized uniquely by an increase of emissions at the 557.7 nm wavelength. The detailed dayside auroral spectra and morphology as a function of MLT are discussed.     

Features of morning-time auroras during SC

The optical observations on Heiss Island and the ion drift measurements on the DMSP F8 satellite were used to study the aurora characteristics and ionospheric convection before and after SC registered at 2330 UT on January 13, 1988. It has been indicated that two zones of luminosity can be distinguished in morning-time auroras during the quiet period before SC: the soft zone with auroral arcs and the harder diffuse auroral zone (equatorward of the first zone). After SC, a gradual smooth activation of auroras in both zones was followed (4–5 min later) by a more abrupt intensification of diffuse luminosity and by the appearance of numerous bright discrete auroras throughout the sky. In the diffuse auroral zone, the variations in the luminosity intensity with a period of 6–7 min were observed after SC. Auroral and geomagnetic field pulsations are closely correlated. During the quiet period before SC, sunward convection was concentrated in the soft precipitation region in the form of jets located in the vicinity of auroral arcs. After SC, considerable sunward convection was observed in the diffuse auroral zone. Peaks of the upward ion drift velocity were registered in the vicinity of auroral arcs.     

基于全天空图像的极光活动变化检测方法研究

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.     

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

We document the detailed dynamics of the dayside aurora in the ≈1200–1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF B_y conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5^MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71^–75^MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ≈100 km equatorward shift of its equatorward boundary, at ≈75^MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5–6 min, and (3) east-west expansion of the higher-latitude aurora (at ≈77^–78^MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100–400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection.     

Response of the night aurora to a negative sudden impulse

Data from the meridian scanning photometers of the NORSTAR network and all-sky cameras of the THEMIS network were used for a detailed study of the response of night auroras to the sharp decrease of the solar wind dynamic pressure on September 28, 2009. The decrease in dynamic pressure was accompanied by a corresponding depression of the magnetic field in the SYM-H index and the origin of a negative sudden impulse (SI) with a duration of 5–8 min and amplitude of 150–200 nT in the horizontal component of the magnetic field at stations of the night sector of the auroral zone. The magnetic impulse was preceded by a long calm magnetic period, although the IMF Bz-component was negative for ~1.5 hour before the SI ^–. The commencement of the SI ^–, which was determined by variations in the magnetic field at ~0650 UT, was accompanied by a sharp increase in the intensity of discrete forms of polar auroras in the midnight sector of the auroral zone and their fast propagation to the pole. Approximately 6–8 min after the SI ^–, the auroral intensity in the emissions, which were excited by the fluxes of precipitated electrons and protons, quickly began to decrease in the night sector. Analysis of the optical observations showed the two-stage character of the response of the night auroras to the SI ^– in the considered event: first, fast movement of the discrete aurora forms to the pole with a significant increase in their intensity, and a further fast decrease in auroral intensity with a delay of ~6–8 min relative to the SI ^–. The possible reasons for such aurora behavior are discussed.     

X射线极光强度与亚暴指数AE的相关关系

研究了Polar卫星的极区电离层X射线成像仪（PIXIE）得到的极光X射线成像强度AI（Auroral Intensity）与磁层亚暴指数的相关关系.本文发现,在所选取的1997年至2001年的部分数据中,从完整的X射线图像得到的极光X射线总强度和AE指数有很好的线性相关关系,在全部83组数据中有566％的数据的线性相关系数都在060以上（相关系数最大为097）.所以本文认为极光X射线总强度可以作为新的磁层亚暴卫星实时监测指数.     

Reconfiguration and closure of lobe flux by reconnection during northward IMF: possible evidence for signatures in cusp/cleft auroral emissions

Observations are presented of the response of the dayside cusp/cleft aurora to changes in both the clock and elevation angles of the interplanetary magnetic field (IMF) vector, as monitored by the WIND spacecraft. The auroral observations are made in 630 nm light at the winter solstice near magnetic noon, using an all-sky camera and a meridian-scanning photometer on the island of Spitsbergen. The dominant change was the response to a northward turning of the IMF which caused a poleward retreat of the dayside aurora. A second, higher-latitude band of aurora was seen to form following the northward turning, which is interpreted as the effect of lobe reconnection which reconfigures open flux. We suggest that this was made possible in the winter hemisphere, despite the effect of the Earth’s dipole tilt, by a relatively large negative X component of the IMF. A series of five events then formed in the poleward band and these propagated in a southwestward direction and faded at the equatorward edge of the lower-latitude band as it migrated poleward. It is shown that the auroral observations are consistent with overdraped lobe flux being generated by lobe reconnection in the winter hemisphere and subsequently being re-closed by lobe reconnection in the summer hemisphere. We propose that the balance between the reconnection rates at these two sites is modulated by the IMF elevation angle, such that when the IMF points more directly northward, the summer lobe reconnection site dominates, re-closing all overdraped lobe flux and eventually becoming disconnected from the Northern Hemisphere.     

基于机器学习的极光图像自动分割方法

极光是太阳风能量注入到极区的指示器,从观测视野中准确分割出极光区域对研究极光演变如亚暴过程有非常重要的意义.本文基于全卷积神经网络提出了一种弱监督极光图像自动分割策略,数据标记时仅需指定极光区域的一个像素点即可,极大解决了机器学习人工标注数据的压力.首先利用简单单弧状极光图像训练一个初始分割模型Model 1,然后基于该模型,结合热点状和复杂多弧状极光图像获得一个增强的分割模型Model 2,最后对分割结果做进一步优化.本文对2003—2007年北极黄河站越冬观测的2715幅极光图像进行了分割,并和最新论文结果及人工标签进行了定量和定性比较,其中分割结果与人工标签的“交并比”高达60%,证明了本文方法的有效性.     

The discovery and the first studies of the auroral oval: A review

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.     

The 4-emission-core structure of dayside aurora oval observed by all-sky imager at 557.7 nm in Ny-Ålesund,Svalbard

A survey of dayside aurora excitation at 557.7 nm, which was acquired from an all-sky imager at Yellow River Station in Ny-Ålesund, Svalbard, shows that there are 4 intense emission maxima in the dayside oval, centered near 0630/76, 0830/76, 1400/75, and 1600/75 (unit: MLT/MLAT), respectively. Tracing the magnetospheric sources of these cores along geomagnetic field lines, the 0830- and 1400-MLT cores correspond with the prenoon and postnoon magnetospheric boundary layers (MBLs), and the 0630- and 1600-MLT cores are located at the dusk and dawn MBLs, respectively. The potential solar wind-magnetosphere dynamic processes resulting in these auroral features are discussed.     

Plasma structure within poleward-moving cusp/cleft auroral transients: EISCAT Svalbard radar observations and an explanation in terms of large local time extent of events

We report high-resolution observations of the southward-IMF cusp/cleft ionosphere made on December 16th 1998 by the EISCAT (European incoherent scatter) Svalbard radar (ESR), and compare them with observations of dayside auroral luminosity, as seen at a wavelength of 630 nm by a meridian scanning photometer at Ny Ålesund, and of plasma flows, as seen by the CUTLASS (co-operative UK twin location auroral sounding system) Finland HF radar. The optical data reveal a series of poleward-moving transient red-line (630 nm) enhancements, events that have been associated with bursts in the rate of magnetopause reconnection generating new open flux. The combined observations at this time have strong similarities to predictions of the effects of soft electron precipitation modulated by pulsed reconnection, as made by Davis and Lockwood (1996); however, the effects of rapid zonal flow in the ionosphere, caused by the magnetic curvature force on the newly opened field lines, are found to be a significant additional factor. In particular, it is shown how enhanced plasma loss rates induced by the rapid convection can explain two outstanding anomalies of the 630 nm transients, namely how minima in luminosity form between the poleward-moving events and how events can re-brighten as they move poleward. The observations show how cusp/cleft aurora and transient poleward-moving auroral forms appear in the ESR data and the conditions which cause enhanced 630 nm emission in the transients: they are an important first step in enabling the ESR to identify these features away from the winter solstice when supporting auroral observations are not available.     

Comparing the latitudinal distribution of the <Emphasis Type="Italic">Pc</Emphasis>1 intensity and the position of subauroral proton spots

The latitudinal position of subauroral proton spots (special proton auroras observed from the IMAGE satellite) has been compared with the Pc1 pulsation intensity distribution determined using the data from the Finnish meridional network of induction magnetometers. It has been indicated that a Pc1 intensity maximum is always observed at the station that is closer to the proton aurora projection. Two Pc1 bands were registered in the event when two proton auroral spots were simultaneously observed at different latitudes. In this case, the Pc1 intensity distribution maximum at lower frequencies was related to a proton auroral spot at a higher latitude and vice versa. Such a spatial correlation between Pc1 pulsations and proton auroral spots, together with the previously established time correlation between these phenomena, demonstrates that subauroral proton spots reflect the region of ion cyclotron instability in the equatorial magnetosphere at the level of the ionosphere.     

Statistical characteristics of the spatial distribution of Pc3-4 geomagnetic pulsations at high latitudes in the antarctic regions

The diumal variations in the parameters of Pc3 (20–60 mHz) and Pc4 (10–19 mHz) pulsations at latitudes of the dayside cusp and polar cap have been studied using data of the magnetic stations of the trans-Antarctic meridional profile for the time interval from January to March 1997 (local summer) under weakly disturbed geomagnetic conditions (AE ≤ 250 nT). The technique for estimating pulsation parameters is based on the separation of the wave packets and noise. The diumal variations in the hourly average parameters of the wave packets in the Pc3 and Pc4 bands and noise in the Pc3-4 band (10–60 mHz)—the average number of wave packets, energy of wave packets and noise, and energy of a single wave packet—turned out to be different for the stations located deep in the polar cap (Φ ～ 87°) and at the latitudes of the dayside polar cusp (Φ ～ 70°) and auroral oval (Φ ～ 66°). Several sources of pulsations caused by different channels of wave energy penetration into the magnetosphere through the dayside cusp, dayside magnetopause, and dawn flank of the magnetotail apparently exist at high latitudes.     

不同地磁活动水平下电离层H+上行的半球对比研究

使用FAST/TEAMS仪器在第23太阳活动周下降相的数据,从地磁活动水平的角度,分别分析在磁静日(Kp≤2⁺)和磁扰日(Kp≥3⁺)时南(SH)、北半球(NH)高纬(>50°)电离层H⁺的上行强度,计算其上行率和净上行积分能通量,以期得到H⁺上行的长期水平并分析地磁扰动期间南、北半球离子上行强度的异同.研究结果表明,磁扰期间上行强度显著加强,平静期南、北半球的平均上行率分别是~15%和~20%,而磁扰期的平均上行率分别增强了1.45倍和1.04倍,磁扰期间南半球上行强度的增长更显著;平静期南半球的上行强度小于北半球,但磁扰期两个半球的上行强度相当;磁午夜和黎明区间受地磁扰动的影响最显著,其磁扰期与平静期上行率的比值(S/Q)最大,同时南半球在各个地方时区间的S/Q值均大于北半球;另外,我们发现磁扰期间的上行率在极光椭圆带下边界附近增幅最明显,而积分通量在上边界附近增加显著.上行源区以平静期的源区为中心从日侧极尖区扩展到磁午夜、且向低磁纬延伸,同时,极尖区上行源区在磁扰期有向晨侧偏移的趋势.     

日侧极光弧的发光强度与沉降电子能谱的相关关系

本文利用中国北极黄河站多波段全天空极光观测数据,选取稳定的日侧极光弧,统计研究了极光强度比I_(557.7)/I_(630.0)与极光发光强度I_(557.7)的相关关系.发现I_(557.7)在午前暖点和午后热点区附近出现极大值,分别为2.2kR和2.9 kR;而I_(630.0)在磁正午出现极大值,为1.5kR.当I_(557.7)从0.1kR增加到10kR时,极光强度比I_(557.7)/I_(630.0)也由0.2增加到9.结合DMSP卫星探测的沉降粒子能谱数据,找到17个DMSP卫星穿越黄河站上空极光弧的事件,共穿越40条极光弧.得到了沉降电子的平均能量正比于极光强度比I_(557.7)/I_(630.0),沉降电子的总能通量正相关于极光强度I_(557.7)的关系式.利用该关系式反演所有极光弧的电子能谱,发现在午前和午后扇区,产生极光弧的沉降电子主要来源于等离子体片边界层;在高纬出现强度较弱的弧,对应等离子体幔区域.在磁正午附近,沉降电子的平均能量较低,极光弧处于低纬一侧,粒子源区主要是低纬边界层.     

基于星点的全天空极光图像参数标定及其验证

全天空极光成像仪是地基极光观测研究的重要仪器设备,从其拍摄的全天空图像数据中能获得极光形态、尺度、激发强度等重要物理参数,因而精确标定全天空图像,对准确获取极光相关物理参数极为重要.本文提出了一种基于星点位置信息对全天空图像进行标定的方法,通过该方法可以确定全天空图像参数(天顶在全天空图像中的像素点位置,地理方位以及视野范围内成像半径与天顶角的关系).利用电离层卫星探测到的极光沉降电子能谱中的"倒V"结构与极光弧之间的对应关系,对星点标定方法获取的全天空图像参数进行了验证.结果显示卫星穿越的"倒V"结构宽度(60±6km、102±6km)与同时全天空极光成像仪观测到的卫星穿越的极光弧宽度(64.7±7km、111.6±7km)几乎一致,这表明本文提出的全天空极光图像参数的星点标定方法是有效和准确的.     

Investigation of the relationship between optical auroral forms and HF radar E region backscatter

The SuperDARN HF radars have been employed in the past to investigate the spectral characteristics of coherent backscatter from L-shell aligned features in the auroral E region. The present study employs all-sky camera observations of the aurora from Husafell, Iceland, and the two SuperDARN radars located on Iceland, Þykkvibær and Stokkseyri, to determine the optical signature of such backscatter features. It is shown that, especially during quiet geomagnetic conditions, the backscatter region is closely associated with east-west aligned diffuse auroral features, and that the two move in tandem with each other. This association between optical and radar aurora has repercussions for the instability mechanisms responsible for generating the E region irregularities from which radars scatter. This is discussed and compared with previous studies investigating the relationship between optical and VHF radar aurora. In addition, although it is known that E region backscatter is commonly observed by SuperDARN radars, the present study demonstrates for the first time that multiple radars can observe the same feature to extend over at least 3 h of magnetic local time, allowing precipitation features to be mapped over large portions of the auroral zone.