On the collocation between dayside auroral activity and coherent HF radar backscatter

The 2D morphology of coherent HF radar and optical cusp aurora has been studied for conditions of predominantly southward IMF conditions, which favours low-latitude boundary layer reconnection. Despite the variability in shape of radar cusp Doppler spectra, the spectral width criterion of 220 m s^–1 proves to be a robust cusp discriminator. For extended periods of well-developed radar backscatter echoes, the equatorward boundary of the 220 m s^–1 spectral width enhancement lines up remarkably well with the equatorward boundary of the optical cusp aurora. The spectral width boundary is however poorly determined during development and fading of radar cusp backscatter. Closer inspection of radar Doppler profile characteristics suggests that a combination of spectral width and shape may advance boundary layer identification by HF radar. For the two December days studied the onset of radar cusp backscatter occurred within pre-existing 630.0 nm cusp auroral activity and appear to be initiated by sunrise, i.e. favourable radio wave propagation conditions had to develop. Better methods are put forward for analysing optical data, and for physical interpretation of HF radar data, and for combining these data, as applied to detection, tracking, and better understanding of dayside aurora. The broader motivation of this work is to develop wider use by the scientific community, of results of these techniques, to accelerate understanding of dynamic high-latitude boundary-processes. The contributions in this work are: (1) improved techniques of analysis of observational data, yielding meaningfully enhanced accuracy for deduced cusp locations; (2) a correspondingly more pronounced validation of correlation of boundary locations derived from the observational data set; and (3) a firmer physical rationale as to why the good correlation observed should theoretically be expected.     

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2.2 kR和2.9 kR;而I_630.0在磁正午出现极大值,为1.5 kR.当I_557.7从0.1 kR增加到10 kR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.

     

Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm

The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F₂ region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O⁺ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min.     

Fine structure of auroras during auroral breakup according to the ground-based and satellite observations

The dynamics and fine structure of auroras before and during 60 auroral breakups, including pseudobreakups and breakups at moderate and high auroral activity, have been studied using the developed method for processing television images. The IMAGE and POLAR satellite and simultaneous ground images of auroras, ground magnetic data, and measurements of IMF and solar wind plasma parameters have been analyzed. The signatures that can be precursors of breakup have been found out in the auroral dynamics and morphology in the spatial—temporal vicinity of breakup. The morphological characteristics of auroral structures have been analyzed statistically. The directions of motion of weak subvisual structures have been determined. The velocities of motion of such structures are presented. The relation of the initial auroral arc bright-ening during breakups and pseudobreakups to the beginning of magnetic activation and formation of rayed structures has been analyzed.     

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.     

高纬向阳侧磁层顶通量传输事件的特性研究——通量管轴线方位及运动分析

本文分析了2001年2月和3月期间Cluster Ⅱ穿越磁层顶前后的观测资料,检测到13个通量传输事件（FTEs）.用多颗卫星磁场测量资料的最小方差分析（MVAB）方法确定FTE的管轴方向（其中6个方向较可靠）.FTE管轴方向的分布和低纬处不同,在磁顶法线坐标系LMN中对M轴有较大偏离,比较靠近L轴.deHoffmann-Teller(HT)分析指出,13个FTEs都存在一个很好的HT参考系,表明它们以一个准稳的MHD结构运动.对垂直于管轴方向的运动分析表明FTEs并不一定和背景等离子体一起对流,它们可快于或慢于背景流,但FTEs的运动和背景流基本沿相同方向,其间可有一不大的夹角.在HT坐标系中,10个FTEs的等离子体速度接近零, 其他3个FTEs的等离子体速度约为局地Alfven波速的14%,都不符合Walen关系.其中北半球事件的Walen曲线为正斜率,南半球事件为负斜率,这说明等离子体沿磁力线（北半球顺着磁场,南半球逆着磁场）流向磁层.     

大尺度场向电流及其与单色极光电子的联系——Swarm卫星观测

Swarm卫星A/C在480 km左右高度伴飞,通过二者磁场观测数据,可在不需假设无限大垂直电流片的情况下更加真实地计算出场向电流（FAC）.本文利用最新的Swarm观测数据,研究了大尺度场向电流的时空分布特征,及其对行星际条件的依赖;结合极光沉降粒子时空分布信息,探究了场向电流可能载流子及其源区.分析发现：（1）IMF B_z分量主要控制FAC的强度大小,B_y分量主要改变FAC的结构与分布,最为明显的是0区FAC;（2）昏侧1区上行FAC与单色极光电子的高发区域具有较高的重合度,且在不同行星际条件下均表现出相类似的纬度分布;（3）在上述区域内,FAC密度与单色极光电子能通量表现出较好的相关性.这表明单色极光电子对昏侧1区上行电流起着重要贡献.

     

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.     

Multi-instrument observations of the dynamics of auroral arcs: a case study

We present results from a multi-instrument study of events on February 13–14, 1996. The data were taken by the EISCAT incoherent-scatter radar, the Sussex, MPI and FMI all-sky cameras, the IRIS riometer and the IMAGE and SAMNET magnetometer networks. Observations from the various instruments are compared to establish the concurrency of the radar, optical and absorption signatures of arcs, and to make a detailed study of their dynamics. The distribution of electric field strength near each arc is determined and the drift velocity of each arc is compared with EISCAT measurements of F-region plasma velocity. Two multiple-onset substorms are studied in detail, the behaviour of each arc depends on the phase of the substorm in which it is observed. Our major points are: (1) All arcs observed during the growth or recovery phases are seen to drift at velocities close to the average convection velocity. In contrast, arcs observed during the expansion phase travel at a significantly different velocity. (2) There is strong qualitative evidence that arcs which drift with the convection are optically less bright than arcs with a large relative velocity with respect to the surrounding plasma so that arc brightening at substorm onset is clearly associated with a sharp increase in relative velocity. (3) The observations confirm the current electrodynamics model of arcs and, moreover, we notice a difference in the conductivity behaviour with respect to the direction of the arc movement. It is generally true that when the band of enhanced electric field is in advance of a moving arc the gradient in conductivity is very sharp at the leading edge of the arc and hence the largest electric fields are seen very close to the arc. When, however, the band of enhanced field follows the moving arc the increase in Pedersen conductivity is more gradual, and in such cases too the maximum electric field strength is observed at greater distances from the optical arc itself.     

A neural network-based ionospheric model for the auroral zone

A new empirical model for the lower ionosphere in the auroral zone, called IMAZ, has been developed, tested and refined for use in the International Reference Ionosphere (IRI) global model. Available ionospheric data have been used to train neural networks (NNs) to predict the high latitude electron density profile. Data from the European Incoherent Scatter Radar (EISCAT), based near Tromsø, Norway (69.58°N, 19.23°E), combined with rocket-borne measurements (from 61° to 69° geomagnetic latitude) make up the database of reliable D- and E-region data.NNs were trained with different combinations of the following input parameters: day number, time of day, total absorption, local magnetic K index, planetary Ap index, 10.7 cm solar radio flux, solar zenith angle and pressure surface. The output that the NNs were trained to predict was the electron density for a given set of input parameters. The criteria for determining the optimum NN are (a) the root mean square (RMS) error between the measured and predicted output values, and (b) the ability to reproduce the absorption they are meant to represent. An optimum input space was determined and then adapted to suit the requirements of the IRI community. In addition, the true quiet electron densities were simulated and added to the database, thus allowing the final model to be valid for riometer absorptions down to 0 dB.This paper discusses the development of a NN-based model for the high-latitude, lower ionosphere, and presents results from the version developed specifically for the IRI user community.     

极光电集流纬度变化特征初步分析

为研究极光电集流地磁纬度分布特征,利用北半球SME台站提供的极光电集流指数,通过时序叠加的方法,分析98-07年极光电集流中心地磁纬度随季节和世界时的分布特征.通过对磁扰程度的分级,分析极光电集流地磁纬度随地磁扰动程度的变化特征.结果表明:1)由于SME台站覆盖范围更广,更多地记录到最大的极光电集流强度,有利于研究极光电集流的变化特征;2)西向板光电集流纬度分布存在与强度相反的季节性变化特征,在春秋出现最低值,冬季、夏季出现最高值;3)在| SML|＜2000 nT时,西向极光电集流地磁纬度随着极光电集流强度的增强,近似以线性关系向低纬迁移.随后伴随SML的进一步增强,西向极光极光电集流中心地磁纬度仍有向低纬迁移的趋势,但主要是在磁纬62°N-63°N之间波动.     

Wave emission during a plasma density jump in the auroral zone of the topside ionosphere according to the APEX satellite data

The intensity of the wave emission in the 0.1–10 MHz band measured in the ionosphere (the APEX satellite experiment) has been presented. A jump of the plasma density and an increase in the emission intensity at a plasma frequency have been registered at altitudes of ～1300 km in the topside auroral ionosphere. The emission intensity in the whistler-mode band nonmonotonically increased along the satellite trajectory near the plasma jump wall. It has been indicated that waveguides could be formed near the wall during damping of electrostatic oscillations generated by precipitating electron fluxes. A spatially nonmonotonous separation of waveguides from the plasma inhomogeneity stretched along geomagnetic field lines is possible in this case.     

基于遥感影像研究宁波地区断裂活动性

利用遥感影像多分辨率、 多光谱以及多传感器相结合的方法, 对浙江宁波地区约1900 km²范围的断裂活动性进行分析判读。 根据断裂的影像特征, 将所判读的断裂分为晚更新世活动, 早、 中更新世活动及第四纪活动不明显3类, 同时对主要断裂的活动性进行了详细分析。 宁波地区主要发育NNE向、 NE向和NW向三组活动构造。 其中NNE向育王山山前断裂, 在TM、 MSS和SPOT影像上都表现出清晰的断层形迹, 切过三处冲积洪积扇, 晚更新世有活动。 走向20°的老鹰山与走向55°的清凉山截然相接显示的线性影像反映出NE向算山-曹隘断裂的形迹, 断裂向宁波盆地延伸, 为宁波盆地规模最大的隐伏断裂。 多时相MSS影像上, 显示出NW向新乐—宝幢和宁波—莫枝活动断层的形迹, 它是深部构造活动在地表的反映, 与走向45°的算山—曹隘断裂, 可能是一组地壳破裂网络。     

A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere

Incoherent-scatter radar and ionospheric sounding are powerful and complementary techniques in the study of the Earths ionosphere. The work presented here involves the use of the Tromsø Dynasonde as a correlative diagnostic with the EISCAT incoherent-scatter radar. A comparison of electron-density profiles shows how a Dynasonde can be used to calibrate an incoherent-scatter radar and to monitor changes in the system. Sky-maps of the direction of Dynasonde echoes are compared with EISCAT-derived density profiles to illustrate how a Dynasonde can be used to measure the drift velocity of auroral features. Vector velocities fitted to Dynasonde echoes are compared with EISCAT-derived plasma velocities. The results show good agreement when the data are taken during quiet to moderately active conditions and averaged over time scales of 30 min or more.     

高纬日侧电离层离子上行的地磁活动依赖性研究

本文对比分析了太阳活动高、低年期间高纬日侧顶部电离层离子上行随地磁活动水平的变化特征.按地磁活动水平, 将DMSP卫星在太阳活动高年(2000-2002年, F13和F15)及太阳活动低年(2007-2009年, F13;2007-2010年, F15)期间的SSIES离子漂移速度观测数据分为三组:地磁平静期(Kp < 3), 中等地磁扰动期(3 ≤ Kp < 5)和强地磁活动期(Kp ≥ 5), 分别统计分析了高纬日侧顶部电离层离子上行特征的时空分布.对比分析发现:(1)太阳活动低年期间, 高纬日侧电离层离子上行发生率以及上行速度峰值均是太阳活动高年的2倍多, 而离子上行通量峰值只有高年的1/6-1/4;(2)在相同太阳活动条件下, 地磁活动水平对日侧电离层离子上行发生率峰值的影响并不明显, 但对离子上行发生率的空间分布有着显著的控制作用:电离层离子上行高发区随地磁活动向低纬度扩展, 并在强地磁活动期间呈现饱和的趋势; (3)日侧顶部电离层等离子体似乎存在两个效率相当的上行区域, 一个位于极尖/极隙区纬度附近, 离子可沿开放磁力线上行进入磁尾; 另一个位于晨侧亚极光区附近, 离子沿闭合磁力线上行, 有可能进入日侧等离子体层边界层.

     

The spatial structure of the dayside ionospheric trough

Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.     

Substorm associated radar auroral surges: a statistical study and possible generation model

Substorm-associated radar auroral surges (SARAS) are a short lived (15–90 minutes) and spatially localised (5° of latitude) perturbation of the plasma convection pattern observed within the auroral E-region. The understanding of such phenomena has important ramifications for the investigation of the larger scale plasma convection and ultimately the coupling of the solar wind, magnetosphere and ionosphere system. A statistical investigation is undertaken of SARAS, observed by the Sweden And Britain Radar Experiment (SABRE), in order to provide a more extensive examination of the local time occurrence and propagation characteristics of the events. The statistical analysis has determined a local time occurrence of observations between 1420 MLT and 2200 MLT with a maximum occurrence centred around 1700 MLT. The propagation velocity of the SARAS feature through the SABRE field of view was found to be predominately L-shell aligned with a velocity centred around 1750 ms^–1 and within the range 500 m s^–1 and 3500 m s^–1. This comprehensive examination of the SARAS provides the opportunity to discuss, qualitatively, a possible generation mechanism for SARAS based on a proposed model for the production of a similar phenomenon referred to as sub-auroral ion drifts (SAIDs). The results of the comparison suggests that SARAS may result from a similar geophysical mechanism to that which produces SAID events, but probably occurs at a different time in the evolution of the event.     

Complex study of the auroral arc dynamics and ionospheric plasma convection in prenoon hours

The dynamics of auroral arcs, observed in the prenoon sector during the 2-h period, has been studied in the context of ionospheric convection. The appearance of an isolated arc, the poleward drift velocity of which pronouncedly exceeded the plasma drift velocity, accompanied the IMF impulse and could result from the Alfvén resonance oscillations of the magnetosphere. Arcs that appeared after the northward turning of the IMF vertical component drifted poleward at a velocity close to the convection velocity. The mechanism of arc generation is related to the flute instability which develops in the region of the large-scale field-aligned current. Flute instability indications are found out in the POLAR satellite data. The study confirms the previously proposed classification criterion for dayside arcs with the source on closed field lines, based on the character of arc drift as compared to convection.     

日侧伴随电子加速的离子上行事件的分布特征

本文基于2005年1月和7月DMSP F13卫星的观测数据, 研究了日侧伴随电子加速的顶部电离层离子整体上行事件的分布特征.结果表明, 离子上行主要发生在磁纬70°~80° MLAT范围内, 加速电子磁层源区对应低纬边界层和等离子体片边界层; 冬季上行存在明显的晨昏不对称性, 主要发生在晨侧(06∶00—09∶00 MLT), 夏季上行主要发生在磁正午(09∶00—15∶00 MLT), 以磁正午为中心近似呈对称分布, 并且冬季离子上行发生率显著高于夏季; 离子上行发生率在中等地磁活动时期显著增强, 上行区域随着地磁活动的增强向低纬度方向扩展; 行星际磁场Bx>0时, 对应等离子体片边界层13∶00—18∶00 MLT和06∶00—09∶00 MLT区域内上行发生率增加, 行星际磁场By的方向会导致上行高发区以磁正午为中心发生反转, 行星际磁场南向时, 上行发生率增强; 冬季离子上行平均速度高于夏季.