Electric potential structures of auroral acceleration region border from multi-spacecraft Cluster data

This paper studies an auroral event using data from three spacecraft of the Cluster mission, one inside and two at the poleward edge of the bottom of the Auroral Acceleration Region (AAR). The study reveals the three-dimensional profile of the region’s poleward boundary, showing spatial segmentation of the electric potential structures and their decay in time. It also depicts localized magnetic field variations and field-aligned currents that appear to have remained stable for at least 80?s. Such observations became possible due to the fortuitous motion of the three spacecraft nearly parallel to each other and tangential to the AAR edge, so that the differences and variations can be seen when the spacecraft enter and exit the segmentations, hence revealing their position with respect to the AAR.     

Application of small-size antennas for estimation of angles of arrival of HF signals scattered by ionospheric irregularities

A modification of the Doppler Interferometry Technique is suggested to enable estimating angles of arrival of comparatively broadband HF signals scattered by random irregularities of the ionospheric plasma with the use of small-size weakly directional antennas. The technique is based on the measurements of cross-spectra phases of the probe radiation recorded at least in three spatially separated points. The developed algorithm has been used to investigate the angular and frequency-time characteristics of HF signals propagating at frequencies above the maximum usable one (MUF) for the direct radio path Moscow-Kharkiv. The received signal spectra show presence of three families of spatial components attributed, respectively, to scattering by plasma irregularities near the middle point of the radio path, ground backscatter signals and scattering of the sounding signals by the intense plasma turbulence associated with auroral activations. It has been shown that the regions responsible for the formation of the third family components are located well inside the auroral oval. The drift velocity and direction of the auroral ionosphere plasma have been determined. The obtained estimates are consistent with the classical conception of the ionospheric plasma convection at high latitudes and do not contradict the results of investigations of the auroral ionosphere dynamics using the SuperDARN network.     

Understanding Substorms in the Magnetotail: Early Development and Recent Progress

This is a concise review of physics of the substorm in the magnetotail. It consists of two parts. The first part summarizes historical developments in the early days of the space age (1960--1975) when the basic concepts such as magnetotail and reconnection were established and the leading model of the substorm was introduced. The second part is an overview of the research conducted in recent years (1995--2010) when very significant advances have been achieved in understanding the substorm physics by virtue of several major satellites missions that addressed the magnetotail physics intensively.      

Day-to-day variability of equatorial anomaly in GPS-TEC during low solar activity period

The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionization anomaly (EIA) crest region is investigated by using dual-frequency signals of the Global Positioning System (GPS) acquired from Rajkot (Geog. Lat. 22.29°N, Geog. Long. 70.74°E; Geom. Lat. 14.21°N, Geom. Long. 144.90°E), India. The day-to-day variability of EIA characteristics is examined during low solar activity period (F10.7∼83 sfu). It is found that the daily maximum TEC at EIA crest exhibits a day-to-day and strong semi-annual variability. The seasonal anomaly and equinoctial asymmetry in TEC at EIA is found non-existent and weaker, respectively. We found a moderate and positive correlation of daily magnitude of crest, Ic with daily F10.7 and EUV fluxes with a correlation coefficient of 0.43 and 0.33, respectively indicating an existence of a short-term relation between TEC at EIA and the solar radiation even during low solar activity period. The correlation of daily Ic with Dst index is also moderate (r = −0.35), whereas no correlation is found with the daily Kp index (r = 0.14) respectively. We found that the magnitude of EIA crest is moderately correlated with solar flux in all seasons except winter where it is weakly related (0.27). The magnitude of EIA crest is also found highly related with EEJ strength in spring (r = 0.69) and summer (r = 0.65) than autumn (0.5) and winter (r = 0.47), though EEJ is stronger in autumn than spring.     

Geomagnetic activity driven by solar wind turbulence

Within the framework of the solar wind—magnetosphere coupled system, intense perturbations in the solar wind, causing geomagnetic storms and substorms, have been widely studied by means of the so-called coupling parameters. However, remarkable variations in the geomagnetic field occur even in absence of such perturbations. In those conditions, solar wind MHD turbulence might have a role. Recent results have shown that solar wind turbulence can be described not only as a mixture of inward and outward stochastic Alfvénic fluctuations, but includes also advected structures, dominated by an excess of magnetic energy.     

暴时极光区热层大气焦耳加热与F区电离耗空的EISCAT雷达观测

利用ＥＩＳＣＡＴ雷达探测数据，分析计算了太阳活动高年夏季发生的一次强磁暴期间，极光区电离层对流电场、电导率以及焦耳加热速率等着重考察了Ｅ区热怪大气焦耳加热和Ｆ区离子摩擦增温与Ｆ区电子密度耗空的关系发现在下午东向极光电集流期间，电子密度最大耗空出现在Ｆ区３００－３２５ｋｍ高度，时间恰在积分的Ｅ区大气焦耳加热量大值和Ｆ区最大离子增温之后５－１０ｍｉｎ，耗空率达７０％。     

Auroral Electrojet Event Associated With Magnetospheric Substorms

The auroral electrojet index is an important index in monitoring and predicting substorms. A substorms usually includes auroral breakup, auroral electrojet event marked by AE increase, energetic particle injection at geosynchronous orbit, mid-low latitude Pi2, etc. However the question whether an auroral electrojet event corresponds to a substorm remains unanswered. Using the auroral electrojet index in 2004, we analyzed five auroral electrojet events and studied their relation with substorms. The results show that there are three kinds of auroral electrojet events: (1) simultaneous rapid increase of westward auroral electrojet and eastward auroral electrojet; (2) rapid increase of westward auroral electrojet and almost unchangeable eastward auroral electrojet; (3) rapid increase of eastward auroral electrojet and almost unchangeable westward auroral electrojet. Most of auroral electrojet events correspond to substorms. However a few auroral electrojet events are not accompanied by substorms. This situation most often occurs for the auroral electrojet event in which eastward auroral electrojet dominates.      

Temporal and spatial variation of equatorial ionization anomaly by using multistation ionosonde data for the 19th solar cycle over the Indian region

The paper deals with the study of temporal and spatial variation of equatorial ionization anomaly (EIA) phenomenon along with its dependence on solar activity and season during the 19th solar cycle by using seven Indian ionosonde stations. Present study is an attempt to carry out the comprehensive study of EIA by using the limited number of ground based instruments. This has been achieved by performing the Gaussian fitting over the latitudinal distribution of F2-region critical frequency (foF2) data. Results reveal that the phenomenon of EIA has a strong dependence on solar activity and seasons. The EIA crest exhibits the feature of latitudinal shifting and expansion with increasing solar activity. It is found out that the effect of solar cycle and seasons on EIA is local time dependent. The observations were also compared with the IRI-2001 model predictions and results reveal that the model values are in general agreement with the observed values with some discrepancies, particularly during the high solar activity period and morning sector. The results have been discussed in the light of relative contribution from transequatorial interhemispheric neutral wind and strength of equatorial fountain process during different local time, season and solar activity levels. Furthermore, an attempt is made to parameterize the location and foF2 of the EIA crest by using the regression analysis. These results can be used to predict the latitudinal position and foF2 of the EIA crest for any given 12-month running average sunspot number (R12).     

极光电激流中的暂态过程

本义分析了极光电激流建立阶段的物理过程，认为在此期间存在着一个正反馈，从而导致一种暂态过程的产生。使用一种简化的物理模型，模拟了极光电激流在建立阶段的物理过程，计算结果表明，极光电激流中的暂态过程确实存在，电流、净电荷和电导率在治极光电激流的方向上均存在着传播的阶跃结构.计算结果与有关观测资料符合得很好.     

行星际磁场（IMF）By分量对磁正午前后区极光嘶声发生率的调制

利用南极极点站（磁纬约７５°）１９８６年３１－３８ｋＨｚ频率的ＶＬＦ波数据和卫星观测的ＩＭＦＢｙ分量数据，分析研究了ＩＭＦ晨昏分量Ｂｙ对高纬ＶＬＦ极光嘶声统计发生率周日分布的影响。结果发现，Ｂｙ对极光嘶声的统计发生率的磁地方对（ＭＬＴ）分布有明显的调制作用。磁正午前后的ＶＬＦ统计发生率不对称，Ｂｙ为正，午后发生率大于午前，Ｂｙ为负，午前发生率大于午后，Ｂｙ极性对夜侧ＶＬＦ发生频次的磁地方时分布也有