第23太阳活动周期太阳风参数及地磁指数的统计分析

日冕物质抛射(Coronal Mass Ejection,简称CME)和共转相互作用区(Corotating Interaction Region,简称CIR)是造成日地空间行星际扰动和地磁扰动的两个主要原因,提供了地球磁暴的主要驱动力,进而显著影响地球空间环境.为深入研究太阳风活动及受其主导影响的地磁活动的时间分布特征,本文对大量太阳风参数及地磁活动指数的数据进行了详细分析.首先,采用由NASA OMNIWeb提供的太阳风参数及地磁活动指数的公开数据,通过自主编写matlab程序对第23太阳活动周期(1996-01-01—2008-12-31)的数据包括行星际磁场Bz分量、太阳风速度、太阳风质子密度、太阳风动压等重要太阳风参数及Dst指数、AE指数、Kp指数等主要的地磁指数进行统计分析,建立了包括269个CME事件和456个CIR事件列表的数据库.采用事例分析法和时间序列叠加法分别对两类太阳活动的四个重要太阳风参数(IMF Bz、太阳风速度、太阳风质子密度、太阳风动压)和三个主要地磁指数(Dst、AE、Kp)进行统计分析,并研究了其统计特征.其次,根据Dst指数最小值确定了第23太阳活动周期内的355个孤立地磁暴事件,并以Dst指数最小值为标准将这些磁暴进一步分类为145个弱磁暴、123个中等磁暴、70个强磁暴、12个剧烈磁暴和5个巨大磁暴.最后,采用时间序列叠加法对不同强度磁暴的太阳风参数和地磁指数进行统计分析.统计分析表明,对于CME事件,Nsw/Pdyn(Nsw表示太阳风质子密度,Pdyn表示太阳风动压)线性拟合斜率一般为正;对于CIR事件,Nsw/Pdyn线性拟合斜率一般为负,这可作为辨别CME和CIR事件的一种有效方法.从平均意义上讲,相较于CIR事件,CME事件有更大的南向IMF Bz分量、太阳风动压Pdyn、AE指数、Kp指数以及更小的Dstmin.一般情况下,CME事件有更大的可能性驱动极强地磁暴.总体而言,对于不同强度的地磁暴,Dst指数的变化呈现出一定的相似性,但随着地磁暴强度的增强,Dst指数衰减的速度变快.CME和CIR事件以及其各自驱动的地磁暴事件有着很多不同,因此,需要将CME事件驱动的磁暴及CIR事件驱动的磁暴分开研究.建立CME、CIR事件及地磁暴的数据库以及获取的统计分析结果,将为深入研究地球磁层等离子体片、辐射带及环电流对太阳活动的响应特征提供有利的帮助.     

Development of substorm bulges during storms of different interplanetary origins

Different solar wind structures are observed: magnetic clouds (MC), recurrent streams (RS), and regions of their interaction with undisturbed solar wind (Sheath and CIR). Three of these structures, Sheath, CIR, MC, are the sources of geomagnetic storms. We have searched for distinctions in the development of substorm bulges occurring during geomagnetic storms connected with the MC, Sheath and CIR. Solar wind parameters were taken from the Wind spacecraft and the auroral bulge parameters were obtained from the Ultra Violet Imager onboard Polar spacecraft. We determined the dimensions of the auroral bulges, the poleward aurora propagation, and the onset latitude of auroral bulges. It is shown that auroral bulges “geometry” is different for the examined types of storms. In consequence, the ratio between longitudinal and latitudinal sizes is also different.     

Indicators of an increase in the flux of relativistic electrons in geostationary orbit during geomagnetic storms

The relation of the fluxes of relativistic electrons in geostationary orbit during magnetic storms to the state of the magnetosphere and variations in the solar wind parameters is studied based on the GOES satellite data (1996–2000). It has been established that, in ～52–65% of all storms, the fluxes of electrons with energies higher than 0.6 and 2 MeV during the storm recovery phase are more than twice as high as the electron fluxes before a storm. It has been indicated that the probability of such cases is closely related to the prestorm level of fluxes and to a decrease in fluxes during the storm main phase. It has been found that the solar wind velocity on the day of the storm main phase and the geomagnetic activity indices at the beginning of the storm recovery phase are also among the best indicators of occurrence of storms with increased fluxes at the storm recovery phase.     

Solar origin of geomagnetic storms and prediction of storms with the use of neural networks

This review deals with how the changes of the large-scale solar magnetic fields are related to the occurrence of solar phenomena, which are associated with geomagnetic storms. The review also describes how artificial neural networks have been used to forecast geomagnetic storms either from daily solar input data or from hourly solar wind data. With solar data as input predictions 1–3 days or a month in advance are possible, while using solar wind data as input predictions about an hour in advance are possible. The predictions one hour ahead of the geomagnetic storm indexD _st from only solar wind input data have reached such high accuracy, that they are of practical use in combination with real-time solar wind observations at L1. However, the predictions days and a month ahead need to be much improved in order to be of real practical use.     

磁层相对论电子通量变化与磁暴/亚暴的关系

本文分析了1 AU处的行星际磁场、太阳风速度、Kp指数、Dst和AE的变化关系,以及它们和地球同步轨道附近相对论电子通量的变化关系.分析说明,当行星际磁场Bz分量出现南向扰动和太阳风速度增大超过500 km/s时,地球磁层中常常发生磁暴/亚暴活动.在磁暴主相期间,相对论电子(能量E≥1 MeV)通量下降;而在磁暴恢复相期间,相对论电子通量恢复上升.但是,只有在伴随有高强度（AE≥500 nT）的持续性亚暴活动的磁暴恢复相期间,相对论电子的通量才能增长到超过暴前通量值,且能量低于300 keV的亚暴电子的通量越高,相对论电子的通量越高,反之则越低.亚暴注入电子数的多少很大程度上决定了磁暴恢复相期间相对论电子数的多少,这说明亚暴活动注入能量低于300 keV的亚暴电子是磁层相对论电子的一个重要来源.     

Regional response of the mesosphere–lower thermosphere dynamics over Scandinavia to solar proton events and geomagnetic storms in late October 2003

The short-term regional responses of the mesosphere–lower thermosphere (MLT) dynamics over Scandinavia to the exceptionally strong solar storms with their accompanying solar proton fluxes on the Earth in late October 2003 have been investigated using radar measurements at Andenes (69°N, 16°E) and Esrange (68°N, 21°E). Several solar activity storms resulted in solar proton events (SPEs) at this time, but a particularly active period of high proton fluxes occurred between 28 and 31 October 2003. The significant temperature drop (∼25 K), detected by the meteor radar at Andenes at altitude ∼90 km, was in line with the enhancement of the proton fluxes and was caused by the dramatic reduction of the ozone in the high-latitude middle atmosphere monitored by satellite measurements. This exceptionally strong phenomenon in late October 2003 was composed of three geomagnetic storms, with the first one occurring in the daytime of 29 October and the other two storms in the nighttime of 29 and 30 October, respectively. The responses of the prevailing wind and the main tides (24- and 12-h tides) were studied in detail. It was found that the response of the MLT dynamics to the first geomagnetic storm occurring in the daytime and accompanied by solar proton fluxes is very different from those to the second and third geomagnetic storms with onsets during the nighttime. Some physical mechanisms have been suggested in order to explain the observed short-term variability of the MLT dynamics. This case study revealed the impact of the SPEs observed in late October 2003 and the timing of the geomagnetic storms on the MLT neutral wind responses observed over Scandinavia.     

行星际扰动和地磁活动对GEO相对论电子影响

利用1988—2010年小时平均的GOES卫星数据,对地球同步轨道(GEO)相对论电子变化进行了统计分析,研究了相对论电子通量(Fe)增强事件的发展过程,探讨了利于相对论电子通量增强的太阳风和地磁活动条件.主要结论如下:(1)GEO相对论电子通量即使是峰值,也具有明显的地方时特性,最大电子通量出现在磁正午时.午/夜电子通量比率随着太阳风速度(Vsw)增加而增大;在Dst-50nT时相对论电子具有规则的地方时变化.在太阳活动下降相,电子通量与各参数的相关性较好,与其相关性最好的Vsw、Kp指数以及三次根号下的太阳风密度(N)分别出现在电子通量前39~57h、57~80h和12~24h.(2)强(日平均电子通量峰值Femax≥104 pfu)相对论电子事件,在距离太阳活动谷年前两年左右和春秋分期间发生率最高,较弱(104Femax≥103 pfu)事件无此特点;大部分强相对论电子事件中,电子通量在磁暴主相开始增加,较弱事件中则在恢复相开始回升.(3)太阳风密度变化对相对论电子事件的发展具有重要指示作用.电子通量在太阳风密度极大值后0~1天达到极小值,太阳风密度极小值后0~2天达到极大值.(4)90%以上相对论电子事件是在磁暴及高速太阳风的条件下发生的,与其伴随的行星际参数和地磁活动指数极值满足以下条件:Vswmax516km/s,Dstmin-31nT,Nmin2.8cm-3,Nmax14.1cm-3,Bzmin-2.9nT,AEmax698nT.(5)磁暴过程中,Dstmin后日平均电子通量大于103 pfu的发生概率为53%左右,强/弱相对论电子事件占总数比例分别为36%/64%左右,磁暴强度对其无影响.磁暴过程中的Vsw、N和AE指数大小对于能否引起相对论电子增强起着指示作用.     

Prediction of maximal daily average values of relativistic electron fluxes in geostationary orbit during the magnetic storm recovery phase

The relation of the maximal daily average values of the relativistic electron fluxes with an energy higher than 2 MeV, obtained from the measurements on GOES geostationary satellites, during the recovery phase of magnetic storms to the solar wind parameters and magnetospheric activity indices has been considered. The parameters of Pc5 and Pi1 geomagnetic pulsations and the relativistic electron fluxes during the prestorm period and the main phase of magnetic storms have been used together with the traditional indices of geomagnetic activity (A _E, K _p, D _st). A simple model for predicting relativistic electron fluxes has been proposed for the first three days of the magnetic storm recovery phase. The predicted fluxes of the outer radiation belt relativistic electrons well correlate with the observed values (R ∼ 0.8–0.9).     

The recovery phase of the superstrong magnetic storm of July 15–17, 2000: Substorms and ULF pulsations

The geomagnetic observations, performed at the global network of ground-based observatories during the recovery phase of the superstrong magnetic storm of July 15–17, 2000 (Bastille Day Event, Dst = ?301 nT), have been analyzed. It has been indicated that magnetic activity did not cease at the beginning of the storm recovery phase but abruptly shifted to polar latitudes. Polar cap substorms were accompanied by the development of intense geomagnetic pulsations in the morning sector of auroral latitudes. In this case oscillations at frequencies of 1–2 and 3–4 mHz were observed at geomagnetic latitudes higher and lower than ～62°, respectively. It has been detected that the spectra of variations in the solar wind dynamic pressure and the amplitude spectra of geomagnetic pulsations on the Earth’s surface were similar. Wave activity unexpectedly appeared in the evening sector of auroral latitudes after the development of near-midnight polar substorms. It has been established that the generation of Pc5 pulsations (in this case at frequencies of 3–4 mHz) was spatially asymmetric about noon during the late stage of the recovery phase of the discussed storm as took place during the recovery phase of the superstrong storms of October and November 2003. Intense oscillations were generated in the morning sector at the auroral latitudes and in the postnoon sector at the subauroral and middle latitudes. The cause of such an asymmetry, typical of the recovery phase of superstrong magnetic storms, remains unknown.     

不同起源地磁扰动期间极光沉降能量的统计研究

尽管对极光沉降能量(HP)的研究已经开展很久,但是关于不同行星际扰动源对HP影响的研究仍然很少.本文基于2001—2008年NOAA极轨卫星数据,对三类不同扰动源,即盔状冕流共转相互作用区(CIRs)、伪冕流CIRs和行星际日冕物质抛射(ICMEs)驱动的中等磁暴期间HP的变化进行时序叠加统计分析,讨论了相关太阳风背景参数、地磁活动强度以及耦合函数的有效性;研究了三类磁暴事件期间HP的南北半球不对称性.结果表明,在磁暴之前盔状冕流CIR磁暴的HP明显低于伪冕流CIR磁暴和ICME磁暴,盔状冕流"磁暴前的平静期"与Newell耦合函数关系密切,而与Russell-McPherron效应关系较小.盔状冕流CIR磁暴主相HP高于伪冕流CIR磁暴和ICME磁暴,可能与盔状冕流相应行星际|B_z|和太阳风数密度均较高有关.此外,在Kp≤4时,冬夏季半球HP的差别随着Kp增加而增加,相应的变化规律符合电导率反馈机制的预测;在Kp>4时,盔状冕流磁暴和ICME磁暴冬季半球的HP大于夏季半球的,伪冕流磁暴事件夏季半球的HP大于冬季半球的或与冬季半球的相近.     

2007-2012年Dstmin≤-50nT的中等以上地磁暴的行星际源统计

地磁暴的行星际源研究是了解及预报地磁暴的关键因素之一.本文研究了2007-2012年间的所有Dst_min ≤-50 nT的中等以上地磁暴,建立了这些地磁暴及其行星际源的列表.在这6年中,共发生了51次Dst_min≤-50 nT的中等以上地磁暴,其中9次为Dst_min≤-100 nT的强地磁暴事件.对比上一活动周相同时间段发现,在这段太阳活动极低的时间,地磁暴的数目显著减少.对这些地磁暴行星际源的分析表明,65%的中等以上地磁暴由与日冕物质抛射相关的行星际结构引起,31%的地磁暴由共转相互作用区引起,这与以前的结果一致.特别的,在这个太阳活动极低时期内,共转相互作用区没有引起Dst_min≤-100 nT的强地磁暴,同时,日冕物质抛射相关结构也没有引起Dst_min≤-200 nT的超强地磁暴.以上结果表明极低太阳活动同时导致了共转相互作用区和日冕物质抛射地磁效应的减弱.进一步,分析不同太阳活动期间地磁暴的行星际源发现:在太阳活动低年(2007-2009年),共转相互作用区是引起地磁暴的主要原因; 而在太阳活动上升期和高年(2010-2013年),大部分(75%,30/40)的中等以上地磁暴均由日冕物质抛射相关结构引起.     

中低纬地区电离层对CIR和CME响应的统计分析

本文利用中低纬日本地区(131°E,35°N)GPS-TEC格点化数据,分析了2001—2009年间109个共转相互作用区(CIR)事件、45个日冕物质抛射(CME)事件引起的地磁扰动期间电离层的响应.结果表明,电离层暴的类型随太阳活动的变化而有不同的变化,CIR事件引发的电离层正相暴、正负双相暴多发生在太阳活动下降年,负相暴多发生在高年,负正双相暴多发生在低年;CME事件引发的电离层正相暴和负相暴多发生在高年.CIR和CME引发的不同类型的电离层暴的季节性差异不大,在夏季多发生正负双相暴.电离层暴发生时间相对地磁暴的时延大部分在-6~6h之间,但CIR引发的电离层暴时延范围更广,在-12~24h之间,而CME引发的电离层暴时延主要在-6~6h之间.中低纬的电离层暴多发生在主相阶段,其中CIR引发的双相暴也会发生在初相阶段.电离层负暴多发生在AE最大值为800~1200nT之间.CIR引起的电离层扰动持续时间较长,一般在1~6天左右,而CME引起的电离层扰动持续时间一般在1~4天左右.     

基于Weimer模型的高纬地磁扰动预测

地磁扰动是空间天气中的重要现象,对地基技术系统具有重要的影响.准确预报地磁扰动可以有效避免重大灾害发生.本文基于Weimer电势和磁势模型发展了高纬地区地磁扰动的模拟方法,并与地面台站观测数据进行了比较.地表磁场扰动主要受电离层电流系统的影响,利用Weimer模式计算出电离层等效电流分布后,基于毕奥-萨伐尔定律推导了地磁扰动三分量与电流的关系,最终计算出地磁扰动量.模型的输入参数为太阳风速度、太阳风密度、行星际磁场和磁偶极倾角.模型计算结果与不同纬度和经度的地磁台站观测结果对比表明本文的计算方法能有效地模拟地磁暴期间地磁扰动特征.本文结果对今后发展高纬地区地磁场预报模型奠定了重要基础.     

The spatial relationship between active regions and coronal holes and the occurrence of intense geomagnetic storms throughout the solar activity cycle

We study the annual frequency of occurrence of intense geomagnetic storms (Dst < –100 nT) throughout the solar activity cycle for the last three cycles and find that it shows different structures. In cycles 20 and 22 it peaks during the ascending phase, near sunspot maximum. During cycle 21, however, there is one peak in the ascending phase and a second, higher, peak in the descending phase separated by a minimum of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle distribution of storms with the corresponding evolution of coronal mass ejections and flares. We find that, as the frequency of occurrence of coronal mass ejections seems to follow very closely the evolution of the sunspot number, it does not reproduce the storm profiles. The temporal distribution of flares varies from that of sunspots and is more in agreement with the distribution of intense geomagnetic storms, but flares show a maximum at every sunspot maximum and cannot then explain the small number of intense storms in 1980. In a previous study we demonstrated that, in most cases, the occurrence of intense geomagnetic storms is associated with a flaring event in an active region located near a coronal hole. In this work we study the spatial relationship between active regions and coronal holes for solar cycles 21 and 22 and find that it also shows different temporal evolution in each cycle in accordance with the occurrence of strong geomagnetic storms; although there were many active regions during 1980, most of the time they were far from coronal holes. We analyse in detail the situation for the intense geomagnetic storms in 1980 and show that, in every case, they were associated with a flare in one of the few active regions adjacent to a coronal hole.     

The relation between geomagnetic pulsations and an increase in the fluxes of geosynchronous relativistic electrons during geomagnetic storms

The dynamics of the Pc5 and Pi1 pulsation characteristics and relativistic electron fluxes at geostationary orbit were comparatively analyzed for three nine-day intervals, including quiet periods and periods of geomagnetic storms. It was shown that relativistic electron fluxes increase considerably when the power of global Pc5 pulsations and the index of midlatitude irregular Pi1 pulsations increase simultaneously. The correlation between the characteristics of Pi1 and Pc5 geomagnetic pulsations and the level of the relativistic electron flux at geostationary orbit during the magnetic storm recovery phase were studied. It was shown that the correlation coefficient of the relativistic electron maximal fluxes during the magnetic storm recovery phase with the parameter of midlatitude Pi1 pulsations is slightly higher than such a correlation coefficient with the solar wind velocity.     

Correlation between the Earth’s outer radiation belt dynamics and solar wind parameters at the solar minimum according to EMP instrument data onboard the CORONAS-Photon satellite

The study of variations in the electron flux in the outer Earth radiation belt (ERB) and their correlations with solar processes is one of the important problems in the experiment with the Electron-M-Peska instrument onboard the CORONAS-Photon solar observatory. Data on relativistic and subrelativistic electron fluxes obtained by the Electron-M-Peska in 2009 have been used to study the outer ERB dynamics at the solar minimum. Increases in outer ERB relativistic electron fluxes, observed at an height of 550 km after weak magnetic disturbances induced by high-velocity solar wind arriving to the Earth, have been analyzed. The geomagnetic disturbances induced by the high-velocity solar wind and that resulted in electron flux variations were insignificant: there were no considerable storms and substorms during that period; however, several polar ground-based stations observed an increase in wave activity. An assumption has been made that the wave activity caused the variations in relativistic electron fluxes.     

Solar-wind–magnetosphere coupling,including relativistic electron energization,during high-speed streams

High geomagnetic activity occurs continuously during high-speed solar wind streams, and fluxes of relativistic electrons observed at geosynchronous orbit enhance significantly. High-speed streams are preceded by solar wind compression regions, during which time there are large losses of relativistic electrons from geosynchronous orbit. Weak to moderate geomagnetic storms often occur during the passage of these compression regions; however, we find that the phenomena that occur during the ensuing high-speed streams do not depend on whether or not a preceding storm develops. Large-amplitude Alfvén waves occur within the high-speed solar wind streams, which are expected to lead to intermittent intervals of significantly enhanced magnetospheric convection and to thus also lead to repetitive substorms due to repetitively occurring reductions in the strength of convection. We find that such repetitive substorms are clearly discernible in the LANL geosynchronous energetic particle data during high-speed stream intervals. Global auroral images are found to show unambiguously that these events are indeed classical substorms, leading us to conclude that substorms are an important contributor to the enhanced geomagnetic activity during high-speed streams. We used the onsets of these substorms as indicators of preceding periods of enhanced convection and of reductions in convection, and we have used ground-based chorus observations from the VELOX instrument at Halley station as an indicator of magnetospheric chorus intensities. These data show evidence that it is the periods of enhanced convection that precede substorm expansions, and not the expansions themselves, that lead to the enhanced dawn-side chorus wave intensity that has been postulated to cause the energization of relativistic electrons. If this inference is correct, and if it is chorus that energizes the relativistic electrons, then high-speed solar wind streams lead to relativistic electron flux enhancements because the embedded large-amplitude Alfvén waves give multi-day periods of intermittent significantly enhanced convection.     

The solar causes of major geomagnetic storms

In this paper we reanalyse the set of ten major geomagnetic storms which occurred between August 1978 and December 1979. We relate them to the characteristics of the solar wind disturbances which caused them and the solar sources of such disturbances as tracked by means of interplanetary scintillation. It seems to us that the shock causing the sudden commencement and the plasma behind it with an important long-lasting B_z south component (B_z     

Relativistic electron losses related to EMIC waves during CIR and CME storms

The losses of radiation belt electrons to the atmosphere due to wave–particle interactions with electromagnetic ion-cyclotron (EMIC) waves during corotating interaction region (CIR) storms compared to coronal mass ejections (CME) storms is investigated. Geomagnetic storms with extended ‘recovery’ phases due to large-amplitude Alfvén waves in the solar wind are associated with relativistic electron flux enhancements in the outer radiation belt. The corotating solar wind streams following a CIR in the solar wind contain large-amplitude Alfvén waves, but also some CME storms with high-speed solar wind can have large-amplitude Alfvén waves and extended ‘recovery’ phases. During both CIR and CME storms the ring current protons are enhanced. In the anisotropic proton zone the protons are unstable for EMIC wave growth. Atmospheric losses of relativistic electrons due to weak to moderate pitch angle scattering by EMIC waves is observed inside the whole anisotropic proton zone. During storms with extended ‘recovery’ phases we observe higher atmospheric loss of relativistic electrons than in storms with fast recovery phases. As the EMIC waves exist in storms with both extended and short recovery phases, the increased loss of relativistic electrons reflects the enhanced source of relativistic electrons in the radiation belt during extended recovery phase storms. The region with the most unstable protons and intense EMIC wave generation, seen as a narrow spike in the proton precipitation, is spatially coincident with the largest loss of relativistic electrons. This region can be observed at all MLTs and is closely connected with the spatial shape of the plasmapause as revealed by simultaneous observations by the IMAGE and the NOAA spacecraft. The observations in and near the atmospheric loss cone show that the CIR and CME storms with extended ‘recovery’ phases produce high atmospheric losses of relativistic electrons, as these storms accelerate electrons to relativistic energies. The CME storm with short recovery phase gives low losses of relativistic electrons due to a reduced level of relativistic electrons in the radiation belt.     

佘山地磁台百年磁暴（二）——极大磁暴分析

本文是佘山地磁台百年磁暴的第二部分,对其极大磁暴（主相ΔH≥400 nT）进行分析.通过与其他三组由不同地磁活动指数定义的极大磁暴对比,表明佘山台用主相幅度差对极大磁暴的定义与之基本相符.同时结合几个典型磁暴,对磁暴与太阳风、行星际磁场和电离层之间的关系进行了讨论.