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.     

极光吸收的日变化与季变化

麦阔里岛和戴维斯站分别位于极光带中心和极光带极向边缘区内.这两处的极光吸收次数在晚间多些,其中突然性吸收主要出现在午夜(当地地磁时间)前,缓变性吸收在午夜后.极光吸收与太阳的活动性密切相关.太阳风高能粒子主要沉降在极光中心带磁午夜区,然后向东西与南北方向扩散,以向西的电射流为主,向东的为辅.但向西的弱些、速度慢些;向东的强些、速度快些.太阳活动增强后,尤其是强的X耀斑事件后,向西的电射流增多增强.另外,在较高磁纬地区的戴维斯站,冬季时极光吸收增多增强.但在极光中心区的麦阔里岛观测站,基本上无此种季节效应.这可能是由于冬季(对南半球而言)极光卵向南偏移造成的.     

A study on the multi-component substrom current

A new technique of eigen mode analysis, Method of Natural Orthogonal Components (MNOC) is used to analyze the ionospheric equivalent current systems obtained on the basis of magnetic data at six meridian magnetometer chains in the northern hemisphere during March 17 19, 1978. The results show that the whole current pattern for any given instant consists of a few eigen modes with different intensities. The first eigen mode exhibits a two cell current construction, characterizing the large scale magnetospheric convection and directly driven process, while the second eigen mode shows a concentrated westward electrojet at midnight sector, characterizing the substorm current wedge and the loading unloading process. The first mode consistently exists whenever during quiet periods or at substorms, and its intensity increases from the beginning of the growth phase of substorms, then quickly intensifies in the expansion phase, followed by a gradual decrease in the recovery phase. On the other hand, the intensity of the second mode remains to be near zero during both quiet time and the growth phase of substorms. Its rapid enhancement occurs in the expansion phase. These characteristics in the current patterns and the intensity variations coincide with the defined physical processes of the directly driven and loading unloading components.     

A comprehensive model current system for high-latitude magnetic activity -II. The substorm component

Summary. In paper I of this series (Hughes & Rostoker) we have presented a composite model three-dimensional current system whose magnetic perturbation pattern is in good agreement with that observed at high latitudes during periods of moderate magnetospheric activity. In this paper we extend the model current system to demonstrate its ability to reproduce the magnetic perturbation pattern associated with the magnetospheric substorms. In agreement with previous workers, we find it necessary to include a region of intense equatorward current flow at the western edge of the westward travelling surge. For the particular substorm event presented in this paper, we find that the main eastward and westward electrojets intensified slightly before the appearance of the surge form, and we are able to evaluate quantitatively the amount of change involved.     

Propagation and source of Pc5 frequency range pulsation at cusp latitude

Two induction magnetometers have been installed at Chinese Zhongshan Station and Australia Davis Station, Antarctica respectively. We adopt the cross spectral analysis technique to analyze the data of the two induction magnetometers, in June, September, December 1996 and March 1997, and to investigate Pc5 frequency range pulsation (150 600 s) occurrence and propagation in cusp latitude. The results are summarized as follows: At Zhongshan Davis Station, the magnetic pulsations in Pc5 frequency band can occurs over a wide time, but more frequently at pre local magnetic noon and pre local magnetic midnight. The Pc5 pulsations have no significant seasonal variation in the amplitude, occurrence and propagation. The amplitude has a small peak at pre local magnetic noon and large value sometimes at pre local magnetic midnight. In daytime, the Pc5 pulsations propagate westward in morning and eastward in afternoon, and reversal at local magnetic noon. In nighttime, the Pc5 pulsations propagate westward before 20:00 MLT and eastward after 20:00 MLT. Near dusk time, the Pc5 pulsations propagate irregularly. These characteristics indicate that the Pc5 pulsations have different source at different local magnetic time.     

Low-latitude infrasonics associated with geomagnetic activity

Summary. Certain associated fluctuations in geomagnetic records and infrasonic pressure variations at ground level noted at Hyderabad and Delhi are discussed with the help of simultaneous records taken during 1980. Typical infrasound signals are noted, apparently generated by the magnetic substorms in the auroral zones and travelling down to near tropical latitudes with speeds in the range of 400–500m s^-1. Characteristic signatures in infrasound records, corresponding to SSCs and storm time fluctuations are also noted, but only when substorms are associated with the storms.     

南极地区地磁扰日变化S_D场特征

利用南极地磁资料研究了地磁扰日变化ＳＤ场特征。１）ＳＤ场变化不如Ｓｑ场变化规则,无明显的昼夜差异;太阳活动高年（１９９１年）比下降年（１９９４年）ＳＤ场变化更强烈。２）极隙区中山站ＳＤ场变幅比亚极光区长城站和北半球低纬区北京台的ＳＤ场变幅大１０倍以上。３）中山站Ｓ０Ｄ（Ｈ）变化呈“正弦波”形态,与长城站和北京台Ｓ０Ｄ（Ｈ）变化形态相反。４）中山站Ｓ０Ｄ等效电流矢量在早晨－下午（０２～１５ｈ）矢量方向为反时针西向,下午－夜间（１５～０２ｈ）矢量方向为顺时针东向,这是由极区东向、西向电射流和极区电流涡旋所引起;长城站与北京台Ｓ０Ｄ等效电流矢量很小,这是由极区东向和西向电射流的影响所致。     

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。     

Unmanned magnetometer network observation in the 44th Japanese Antarctic Research Expedition: Initial results and an event study on auroral substorm evolution

In the 44th Japanese Antarctic Research Expedition (JARE-44) during 2003 to 2004, four unmanned magnetometers were deployed in Antarctica to establish a observation network for studying ionospheric and magnetospheric phenomena. Three of them were set about 80 km from Syowa Station, and the fourth was set at Dome Fuji Camp, about 800 km from Syowa. Observations were carried out continuously with a maximum sampling rate of 1 Hz. The purpose of the close network around Syowa was to observe the two-dimensional distribution of the ionospheric equivalent current in a localized area within the field-of-view of the all-sky auroral imager operated at Syowa. Dome Fuji is located at the higher-latitude edge of the auroral zone, while Syowa is located in the middle of it. Auroral observations using the all-sky imager were also carried out at Dome Fuji in 2003. The simultaneous auroral and magnetic observations both at Dome Fuji and Syowa enabled us to study auroral activities in a larger area. This paper describes, the deployment and performance of the unmanned magnetometers in the JARE-44. One auroral substorm event is analyzed in detail to show the usefulness the unmanned magnetometer network.     

Observation of electric currents in the Alaska oil pipeline resulting from auroral electrojet current sources

Summary. Currents in the 1.28 × 10³ km Alaska oil pipeline, induced from the ionospheric, auroral electrojet, were measured at three sites, near Fairbanks, Paxson and Valdez, Alaska, using a gradient configuration of two fluxgate magnetometers. The observed pipeline current magnitudes, which reached 50 A during times of mild geomagnetic activity, displayed a linear relationship with the electric earth potential. Using the induction relationship between the electric and magnetic fields and the typical spectral composition of the geomagnetic field at high latitudes, I obtained a spectral appearance of the current that shows a maximum in the range of 4.5- to 10-min period. Near Fairbanks the pipeline current amplitudes, I (Amperes), could be represented, approximately, by I = 0.65 B _x T ^−0.5, where B _x(nT) is the north—south geomagnetic field variation amplitude and T (min) is its apparent period. There is much less pipelines current at the sites south of Fairbanks. A previously established relationship between the local electric field and the planetary geomagnetic activity index, Ap , permitted a prediction of the pipeline current surge amplitudes in the Fairbanks region as approximately I = 5.0 Ap . Current surges larger than 500 A may be expected rather often in the Alaska pipeline during large geomagnetic storms.     

A study of geomagnetic storms

Summary. An attempt is made to find interplanetary magnetic field and solar-wind parameters which control the development of geomagnetic storms. For this purpose, the interplanetary energy flux is estimated in terms of the Poynting flux ( E × B /4π), and its time variations are compared with the rate of energy dissipation in terms of the ring-current particle injection u _i( t ), Joule dissipation in the ionosphere u_j ( t ) and auroral particle injection u_p ( t ) for 15 major geomagnetic storms.
It is shown that the growth of geomagnetic storms, namely the time variations of the rate of the total energy dissipation, u ( t ) = u _i( t ) + u _j( t ) + u _p( t ), is closely related to the Poynting flux by the following relation:
where l ₀≅ 7 R _E and θ' is a measure of the angle between the interplanetary magnetic field vector and the magnetospheric field vector at the front of the magnetosphere in the equatorial plane. Further, it is shown that within a factor of 2 for each storm period.
A large increase of u ( t ) is associated with substorm activity. Thus, the energy flux ɛ( t ) entering the magnetosphere is dissipated through magneto-spheric substorm processes within the magnetosphere, and their accumulated effects can be understood as geomagnetic storm phenomena.     

极区极夜期间E层占优电离层的分布特征

E层占优电离层是指E层的峰值电子密度大于F层的峰值电子密度（N_mE>N_mF）时的电离层,记为ELDI（E-Layer Dominated Ionosphere）。针对ELDI,利用2007-2010年的COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate satellite)掩星数据,在修正地磁纬度-磁地方时标系下统计分析了它在南北极区极夜期间（南北半球的冬至日前后30天）的分布特征,结果表明极夜期间电离层ELDI特征明显,其分布与极光椭圆位形基本一致,而且其在夜侧的发生率较高,特别是磁子夜之后,北极为70%左右,而南极为90%左右;另外南极的ELDI特征在磁纬度分布上要略宽于北极的分布范围。在ELDI高发区,电离层峰值电子密度要高于其两侧地区,特别是在夜侧,尤其是磁子夜前的峰值电子密度要接近甚至大于磁正午的峰值电子密度,在南极地区格外明显;而且ELDI高发区内的E层的电子含量（TECE）、电离层总电子含量（TECI）及TECE占TECI的比重（TECEI）都高于其两侧地区,北极TECE和TECI大于南极,而TECEI则是南极大于北极。这些现象主要是由于极夜期间极区高能粒子沉降引起底部电离层电离率增大所致;同时,由于地磁轴偏离地理轴的程度在南极要大于北极,使得极夜期间南极地区的电离层的电子密度,特别是在F层要相应地小于北极地区,从而导致了极夜期间南北半球极区电离层ELDI特征之间差异。     

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.     

Annual variation of the geomagnetic field

Summary. Horizontal and vertical intensity data, obtained between 1957.0 and 1961.0 at 69 observatories, are analysed to determine the worldwide distribution of the annual variation of the geomagnetic field. Only data observed near local midnight are used, to avoid the small, but significant contamination from Sq. Over most of the world the variation is found to be small, with a clear dependence on latitude, but near the poles it is larger and more erratic. The non-polar variation is subjected to spherical harmonic analysis and separated into parts of internal and external origin. The polar variations are shown to be consistent with a north—south oscillation of the mean position of the auroral electrojets during the year. It is suggested that, with the exception of the polar effect, the annual variation is not due to ionospheric currents (as was hitherto believed), but results from an annual variation in the latitude of the ring current.     

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。     

The auroral occurrence over Zhongshan Station, Antarctica

The auroral data observed by all sky TV camera during 1995 and 1997 at Zhongshan Station of Antarctica are used to analyze the statistic characteristics of the aurora over Zhongshan Station. Around postnoon (1200 - 1600UT ) and midnight (2000 - 0100 UT ), the aurora appears more frequently and stronger than those in evening (1600- 2000UT ). The corona type auroras mainly occur at poleward and overhead of Zhongshan Station during postnoon and around midnight. The hand type auroras mainly appear during postnoon. while during evening and around midnight only appear at equatorward. The active surges mostly appear around midnight,while the transpolar arcs mainly occur after midnight. Except for the transpolar arcs. the occurrences of the other three type auroras are related with Kp index. Usually Zhongshan Station enters the auroral oval at postnoon,the exact time depends on Kp index.     

南极中山站极光形态的统计特征

利用极光全天空摄象机１９９５年和１９９７年在南极中山站观测的极光数据,对中山站上空极光的出现情况进行了统计分析。在南极中山站,午后（磁地方时１４００～１８００ＭＬＴ）和子夜前后（２２００～０３００ＭＬＴ）出现极光的情况比较多,在傍晚（１８００～２２００ＭＬＴ）出现极光的情况要少一些;较强的极光主要也出现在午后和子夜附近。冕状极光主要出现在子夜附近和午后的极向侧和天顶,在傍晚出现很少;带状极光主要出现在午后和赤道侧的傍晚与子夜;极光浪涌主要出现在子夜前后;向日极光弧则主要出现在子夜前后,子夜前比子夜后多,极向和天顶比赤道侧多。除向日极光弧外,其它形态的极光在中山站的出现情况与Ｋｐ指数相关。中山站进入极光带的时间通常在午后,具体时间也与Ｋｐ指数有关     

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.     

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。     

极区电离层F区加热激发极低频波研究

"极区电急流天线"辐射依赖于低电离层D/E区背景电急流,而高电离层F区极低频调制加热,可产生抗磁性电流,形成极低频波辐射源。利用电离层F区一维时变加热数值模型,采用全波解算法研究高纬Troms(69.59°N,19.23°E)地区电离层F区极低频调制加热。模拟结果表明,极区高电离层激发的极低频波与极区低电离层激发的结果不同。加热泵波的有效辐射功率(effective radiated power,ERP)、调制频率及电离层背景对极低频波强度有着重要影响。