极隙区极光粒子沉降对电离层影响的模拟研究

利用一维自洽的时变极区电离层模型,研究极隙区极光粒子沉降对极区电离层F层电子密度影响的时变过程。假设一维时变电离层模型描述的磁流管中F层等离子体在对流作用下经过极隙区,随对流路径的不同,磁流管在极隙区经历的时间不同,以此考察极光粒子沉降作用下电离层随时间的演化过程。数值计算结果表明,当磁流管在极隙区停留的时间足够长,F层电子密度能显著增大。然而在磁流管经历极隙区实际时间较短的情况下,极隙区极光粒子沉降对F层电子密度的影响并不大。本文还给出了统计对流模型作用下磁流管在经历极隙区时,有沉降粒子作用和没有沉降粒子作用两种情况下,F层等离子体的时间变化过程的差异。     

极区电离层NmF2观测与国际参考电离层对比研究

利用南北极极隙区与极光带纬度3个台站对电离层F₂层峰值电子密度(N_mF₂)长达1个太阳活动周的观测数据,对国际参考电离层IRI-2016模型在极区的适用性进行系统的定量研究。结果表明,在极光带纬度的北极Troms?站,IRI预测与观测符合最好,大部分季节相对误差在40%以内,在太阳活动高年略好于太阳活动低年。在极隙区纬度的南极中山站和Longyearbyen站,IRI预测精度在太阳活动低年高于太阳活动高年。在中山站和北极Longyearbyen站仅个别月份相对误差在20%以内,大部分月份相对误差超过40%,冬季相对误差接近100%,特别是Longyearbyen站,在太阳活动高年冬季相对误差超过100%。从季节上看,3个台站都是冬季符合最差,夏季符合最好。IRI-2016模型对极区电离层进行预测时,难以如实反映极区等离子体对流和能量粒子沉降等极区特有的物理过程对极区电离层N_mF₂的影响。     

极区ELDI随太阳活动的变化特征—— EISCAT/ESR雷达观测

利用1999—2011年EISCAT(EISCAT Tromsø UHF)和ESR(EISCAT Svalbard Radar)雷达的场向电子密度观测数据, 对比分析了两处雷达观测到的极区E层占优电离层ELDI (E-Layer Dominated Ionosphere)事件在太阳活动高、低年的统计特征。地面雷达观测表明, 太阳活动水平对极区ELDI发生率的空间分布影响显著: 在太阳活动高年, ELDI在EISCAT雷达处(极光椭圆区纬度)的发生率高于ESR雷达处(极尖/极隙区纬度); 在低年则恰好相反。夏季似乎不利于ELDI的发生, 且在该季节的变化特征不受太阳活动水平及空间位置变化的影响。两部雷达在太阳活动高年观测到ELDI的季节变化规律分别与低年期间的结果相一致: 在冬季和早春, ELDI的发生率较高, 其他季节发生率较低, 夏季尤其低。在ELDI事件期间, 两处雷达观测到事件的持续时间和电离层E层厚度随太阳活动水平的变化表现出明显差异: 高年事件的持续时间总体上比低年短, 低年观测到ELDI的厚度要小于高年结果; 然而N_mE/N_mF₂比值及H_mE却没有表现出明显依赖。     

极隙区纬度太阳活动高年背景电离层特征

本文利用 EISCAT-Svalbard 雷达1999年3月至2003年2月期间观测数据,对太阳活动高年前后极区电离层 F 区电子密度随高度和地方时的二维分布进行统计分析,研究极隙/极盖区背景电离层特征,并与 IRI-2001模式预测结果进行比较。分析结果表明,在 ESR 雷达所在纬度,不存在“冬季异常”现象;但首次发现,此处电离层冬季日变化存在磁午夜前主极大。另外,无论在什么季节,白天时段 ESR 雷达上空电子密度都在磁正午附近有一极大值。与 IRI 模式的比较表明,模式预测的 F 区电子密度与 ESR 实测结果存在较大偏差,在500km 高度以上的顶部电离层和冬季,差别尤其明显。简要讨论了软粒子沉降对造成电子密度日变化磁正午极大的作用和冬季磁午夜前主极大的形成机理。     

太阳活动低年南北极电离层F2层观测与国际参考电离层对比研究

利用2006-2007年EISCAT Svalbard雷达(ESR)和南极中山站DPS-4测高仪的观测数据,对太阳活动低年不同季节的极区电离层F2层临界频率(f0F2)和峰值高度(hmF2)进行统计分析,研究其日变化特征,并与国际参考电离层IRI-2007模式比较.结果表明,在太阳活动低年,夏季两站的观测结果与IRI预...     

南极中山站的f_0F2特征

本文利用电离层数字测高仪 (DPS - 4)所测的f0 F2和从美国NOAA和DMSP卫星观测估算的半球功率指数和午夜极光区赤道侧边界纬度等资料 ,考察中山站电离层的极区特征。结果表明 ,冬季中山站电离层内的电离生成主要取决于从磁层沉降的粒子。在太阳活动和地磁变化宁静环境下 ,磁正午极隙区内的软粒子是最主要的电离源 ,它能使f0 F2达全天的最大值 ;上、下午各有数小时处于极光带内时 ,高能粒子的电离作用也很重要 ;夜间进入极盖区后 ,电子密度则很低。夏季太阳辐射电离效应使f0 F2值比冬季增加 1- 1 .5MHz,而其日变化的最大值时间也提前了 1- 2hr。发生很大扰动时 ,极隙区和极光带的位置均向低纬方向移动。若中山站日间也处于极盖区内时 ,电子密度会大幅度下降 ,并常接收不到电离层回波的信号。在中等扰动环境下情况更加复杂。由于高纬电离层对流速度很高 ,离子 /中性分子间的碰撞复合系数就很大。热层中性大气全球经向环流对高纬电离层电子密度的增加无显著作用。磁暴期间中午从极隙区向南的等离子体对流对中山站f0 F2的增高也无明显影响。     

北极区低电离层加热效应的数值模拟研究

从等离子体能量守恒方程和连续性方程出发,以国际参考电离层(IR I2000)和大气模型(MSIS)为背景,通过数值方法模拟研究大功率无线电波对北极低电离层的电子密度和电子温度的扰动效应。结果表明,在外加强电磁场作用下,电离层等离子体中的带电粒子(主要是电子)动力学温度得以升高而产生等离子体温度扰动;由于电子温度升高,等离子体碰撞频率增加且电子的复合系数减小,诱发电子密度扰动;电子密度和电子温度的扰动幅度随着加热时间的推移而减小,即扰动趋于饱和;电子密度扰动的弛豫时间较电子温度扰动的弛豫时间大;在泵波频率大于电离层临界频率的条件下,泵波频率越高,其激发的电子温度和电子密度扰动效应也就越弱。     

极盖区等离子体云块触发的极向边界点亮事件的观测研究

极盖区等离子体云块是电子密度比背景高出2倍及以上的高密度不均匀体,极向边界点亮是夜侧极光卵极向边界亮度显著增强的极光结构。探究极盖区等离子体云块与极向边界点亮现象的形成和演化以及二者之间的关系对理解极区电离层-磁层耦合具有重要意义。本文基于北极黄河站全天空极光成像仪、欧洲非相干散射雷达(EISCAT)、SuperDARN雷达和GPSTEC等多手段观测数据,揭示极盖区等离子体云块运动到夜侧极光卵极向边界,进而触发极向边界点亮的完整过程。研究结果表明,(1)高密度等离子体云块从极盖区运动到夜侧极光卵极向边界时,极向边界附近的极光强度明显增加,即出现了极向边界点亮现象。(2)极光亚暴发生后,极光卵极向膨胀,极向边界到达EISCAT Svalbard 42 m雷达观测视野。该雷达观测到了高密度、高电子和离子温度的结构,并伴随着电子密度峰值高度下降和离子上行等现象,这与高密度等离子体云块的输运和当地的极光粒子沉降密切相关。(3)从日侧向夜侧输运的等离子体云块到达夜侧极光卵极向边界附近时可能触发极向边界点亮,并且影响等离子体云块和极光粒子沉降接触区域的等离子体特征,这有助于加深我们对夜侧极区电离层...     

GNSS广播电离层模型在极区的改正效果分析

电离层时延为GPS测量中最棘手、最严重的误差源,而极区结构复杂波动较大,电离层延迟极大影响了GPS测量精度,故在极区选取一个简单有效的电离层模型极为重要。将GPS及BDS采用的不同Klobuchar模型以及Ne Quick模型计算的极区总电子含量,以欧洲定轨中心提供的GIM模型电离层产品作为参考标准,研究三种广播电离层模型在北极地区的均方根和模型改正率。选取了2009—2013年共计5年的时间数据进行分析。结果表明,纬度在57.5°以上地区电离层改正GPS系统采用的Klobuchar模型基本不适用,但改正效果依然优于BDS,而Ne Quick模型改正效果弱于中低纬度,改正率整体在40%左右。     

南北极冬季F2层电离层特性对比研究

利用南极中山站和北极Tromso站1996、1997、1998及2002年的测高仪观测数据,对中山站(6月份)和Tromso站(12月份)上空冬季foF2的日变化特性进行了对比研究,结合数值模拟结果,分析了中山站和Tromso站F2层电离层的极区特征,进一步揭示了极区电离层特征的形成机理。结果表明,中山站和Tromso站虽然地理纬度接近,foF2日变化形成机理不完全相同。由于地磁纬度的差异,极区对流与日侧光致电离的相互作用造成了两站日侧电离层的不同变化形态,中山站foF2日变化主峰出现在磁地方时中午附近,而Tromso站foF2日变化主峰出现在地方时正午附近;两站日侧foF2受太阳辐射流量影响较大,极光沉降粒子电离在太阳活动低年对中山站foF2日变化形态影响显著。     

Auroral Infrasonic Waves and Poleward Expansions of Auroral Substorms at Inuvik, N.W.T., Canada

Summary Observations at Inuvik (70.4° dipole latitude) have shown that supersonic motions of auroral arcs that sweep across the zenith from south to north during poleward expansions of auroral substorms do not generate observable auroral infrasonic waves. This is in contrast to the fact that equator-ward supersonic motions of similar auroral arcs do produce large amplitude infrasonic bow waves. These results imply an asymmetry in the basic generation mechanism of infrasound within the auroral electrojet arcs.     

极光区高空物理过程与磁层-电离层耦合

极区高空物理现象之观测具有悠久历史。对极区地磁、电离层和极光现象的深入考察将地球物理的研究领域扩展到了外层空间,并提出了太阳风－磁层－电离层－热层间耦合这一重要课题。耦合物理机制的证实不仅是火箭、卫星探测的重要贡献,而且也是基于对地面雷达和遍及全球大陆的地磁台站、电离层垂测站之长期观测成果。对流电场、一区和二区场向电流、电离层扰动电流系（包括极光区电集流）,以及电导率的分布和变化乃是一有机整体,对其每一环节的深入认识均与对整体的全面了解密不可分。有关的理论和模式研究则有助于人们深入理解各个耦合过程的相互关系,以及其各发展阶段中不同物理过程的相对重要性。     

南极中山站极光电集流分布特征分析

本文通过 1 997年在南极中山站观测的极光和所对应的地磁场扰动 ,利用 AU、AL、AE指数描述极光电集流在南极中山站的分布规律及其强度 ,我们发现东向极光电集流强度是正值 ,西向极光电集流强度是负值 ,从绝对值来说 ,西向极光电集流强度大于东向极光电集流强度。南极中山站夏季的极光电集流强度大于冬季的极光电集流。秋夏冬季节的东向极光电集流在72 0～ 1 44 0分 (世界时 1 2～ 2 4时 )的分布规律的拟合曲线类似口朝上的抛物线形 ;西向极光电集流在 72 0～ 1 44 0分这段时间的分布规律的拟合曲线类似正弦波形。了解了极光电集流在南极中山站的分布特征 ,有利于极区电离层和磁层耦合及极光动力学的研究。     

Analysis of S~p_q current systems by using corrected geomagnetic coordinates

The S~p_q equivalent current system of the quiet day geomagnetic variation in the polar region is very complicated. It is composed of several currents, such as the ionospheric dynamo current and the auroral electrojet caused by the field aligned current. S p q is unsymmetrical in both polar regions. In this paper, the S p q current systems are analyzed in the corrected geomagnetic coordinates (CGM) instead of the conventional geomagnetic coordinates (GM), and the symmetries of the S p q current in different systems are compared. Then the causes of S p q asymmetry in the GM coordinates are discussed; the effects of each component in S p q are determined.     

Localization of VLF ionospheric exit point by comparison of multipoint ground-based observation with full-wave analysis

In order to estimate the dynamic structure of the VLF ionospheric exit point, we conducted multipoint ground-based observation of the natural VLF emissions at three unmanned sites: West Ongul (69°01′ S, 39°30′ E), Skallen (69°40′ S, 39°24′ E), and H100 (69°18′ S, 41°19′ E) around Japanese Syowa station, Antarctica, during a whole year of 2006. In this observation, we developed three sets of unmanned autonomous observation systems for natural VLF emissions. Each observation system consists of two crossed vertical loop antennas to pick-up North–South (NS) and East–West (EW) magnetic components, a multi-channel analyzer, and a data logger. The intensity and polarization of NS and EW magnetic components are obtained in 4 spaced frequency (0.5, 1.0, 2.0, and 6.0 kHz) channels by the multi-channel analyzer.The VLF emissions observed at the three sites exhibit an interesting difference in the wave intensity as well as the polarization that allows important information about the locations of their ionospheric exit point to be determined. Firstly, to find the distinct exit point, we have theoretically calculated the spatial distributions of the wave intensity and the polarization on the Earth for VLF whistler mode waves coming down from the magnetized ionosphere, by using the full-wave analysis. Then, we have compared the calculated results with the observed data, to evaluate the possible locations of the ionospheric exit point for the auroral hiss events.As an example, the direction of the estimated ionospheric exit point for the auroral hiss event at 31 March 2006 was found to be consistent with a bright aurora region. However, in this case, the estimated ionospheric exit point was located a few hundred kilometers equatorward of the associated aurora. This would suggest that the ray paths for the auroral hiss could be different from the directions of the geomagnetic field lines for auroral precipitation.     

An improved geomagnetic data selection algorithm for global geomagnetic field modelling

A spherical harmonic degrees 60, global internal field model is described (called BGS/G/L/0706). This model includes a degree 15 core and piecewise-linear secular variation model and is derived from quiet-time Ørsted and Champ satellite data sampled between 2001.0 and 2005.0. For the satellite data selection, a wide range of geomagnetic index and other data selection filters have been used to best isolate suitably quiet magnetospheric and ionospheric conditions. Only a relatively simple, degree one spherical harmonic, external field model is then required. It is found that a new 'Vector Magnetic Disturbance' index ( VMD ), the existing longitude sector A indices, the auroral zone index IE , and the polar cap index PC are better than Kp and Dst at rejecting rapidly varying external field signals at low, middle, auroral and polar latitudes. The model quality is further enhanced by filling spatial and temporal gaps in the quiet data selection with a second selection containing slightly more disturbed data. It is shown that VMD provides a better parametrization than Dst of the large-scale, rapidly changing, external field. The lithospheric field model between degrees 16 and 50 is robust and displays good coherence with other recently published models for this epoch. BGS/G/L/0706 also shows crustal anomalies consistent with other studies, although agreement is poorer in the southern polar cap. Intermodel coherency reduces above about degree 40, most likely due to incompletely filtered signals from polar ionospheric currents and auroral field aligned currents. The absence of the PC index for the southern hemisphere for 2003 onwards is a particular concern.     

A study of two polar magnetic substorms with a two-dimensional magnetometer array

Summary. The paper reports studies of the three-dimensional magnetospheric—ionospheric current systems which produced polar magnetic substorms on 1974 September 7 and September 18. The data were magnetic perturbation fields observed with a two-dimensional array of 23 three-component magnetometers located in western Canada beneath the auroral oval. In an earlier study of a substorm of September 11 (Bannister & Gough) the fields fitted calculated field for a Boström Type 1 current loop with field-aligned currents at east and west ends of the ionospheric segment, and with uniform current density across the width. The substorms here reported could not be modelled with uniform current density. An inverse method due to Oldenburg was therefore used to estimate current density distributions, and satisfactory fits of calculated to observed field resulted. Each substorm was modelled at six representative epochs. In general the principal ionospheric current seem by the array was westward. At four epochs of the September 7 substorm and throughout the September 18 substorm, significant eastward ionospheric current (or its equivalent in terms of the fields produced) was observed north of the westward electrojet. Northwestward bends in the ionospheric current segments were found at four epochs on September 7 and at three epochs on September 18. As in the September 11 substorm (Paper 1), these bends were either west of or close to magnetic midnight. In some cases the bends may follow the auroral oval, but in others they are sharper and may be associated with the Harang discontinuity. East of geomagnetic the ionospheric currents tend to run in a constant geomagnetic midnight latitude range. The developments of the three substorms, of September 7, 11 (Paper 1) and 18, are compared. They showed a variety of shifts in longitude, though all moved eastward relative to magnetic midnight.     

Development of a polar magnetic substorm: a two-dimensional magnetometer array study

A polar magnetic substorm on 1974 September 11 was recorded by a two-dimensional array of 25 three-component magnetometers, so located that the westward ionospheric current passed over the array. The mean perturbation fields over five-minute intervals are presented at six representative epochs of the substorm, the first just before its onset and the sixth 21/2 hr later in the coda of the event. At four of the resulting 'time frames', the perturbation fields have been fitted, on a least-squares criterion, by calculated fields of three-dimensional current loops having downward field-aligned current at the east end of the ionospheric westward current, upward field-aligned current at the west end and closure in the magnetotail. The current density was constant across the width of each of these model currents. In three of the four time frames it proved necessary to introduce a bend to the northwest in the ionospheric current; this bend occurred within 27° (geomagnetic) west of geomagnetic midnight. An association with the Harang discontinuity is possible. The field-aligned current nearer to the array (in one time-frame the downward, east-end current, in two others the upward current at the west end) proved essential to secure any reasonable fit to the data. The ionospheric segment of the current loop moved at least 20° of longitude eastward, relative to the surface of the earth, between 07.48 and 08.58 UT. In this 70-min period the ionospheric segment moved at least 38° eastward relative to magnetic midnight.     

南极中山站冬季电离层的平均特性

本文利用南极中山站的数字式电离层垂直测高仪１９９５年的频高图资料，对中山站上空冬季电离层的一些平均特性进行了初步分析。中山站冬季电离层Ｆ层很不稳定，其日变化比较明显，ｆｏＦ２的月中值在０９００ＵＴ出现极大并在１４００ＵＴ附近出现次极大。最大值在０９００ＵＴ（磁中午）附近，这是极隙区软电子沉降、极区等离子体对流和光辐射电离效应等诸多因素综合作用的结果，形成了所谓的磁中午异常。在２０００～０１００ＵＴ之间ｆｏＦ２数值较小，可能是由于这段时间中山站正处于电离层极洞区域。Ｅｓ层几乎每天都可以观测到，在１７００ＵＴ附近出现机率较高，并且ｆｏＥｓ数值较大，多数为极光型Ｅｓ，主要是由于极光粒子沉降引起的。电离层Ｅ层的变化相对平缓。