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1.
磁暴的发生与环电流的变化密切相关.除了对称环电流外,部分环电流在磁暴的发展过程中也起到了重要的作用,同时部分环电流通过场向电流与极区电离层中的电流形成回路.本文应用INTERMAGNET地磁台网北半球中低纬区域地磁台站数据,对不同强度4个磁暴事件主相和恢复相期间部分环电流和场向电流的磁地方时分布进行了分析和讨论.对于每一个磁暴事件,在低纬地区（地磁纬度约0°—40°N）选用地磁经度上大致均匀的8个台站,通过坐标转换计算平行于磁偶极轴的地磁场水平分量H来分析磁暴期间环电流所引起的磁场扰动;在低纬地区8个台站的基础上增加中纬地区（地磁纬度约40°N—60°N）地磁经度上大致均匀的6个台站,计算地磁坐标系下地磁场东西分量Y来分析磁暴期间场向电流在中低纬地区引起的磁场扰动.结果表明,磁暴主相期间的部分环电流主要作用于磁地方时昏侧和夜侧扇区,并且主相和恢复相期间部分环电流引起的磁场变化随着磁暴级别的增大而增大;磁暴主相期间向下的场向电流多出现在夜侧至晨侧扇区,向上的场向电流多出现在昏侧至午后扇区,且中纬地区向下和向上场向电流的展布范围明显大于低纬地区;恢复相期间弱、中磁暴事件的场向电流呈现与部分环电流相同的减弱趋势,而强、大磁暴事件在恢复相末期场向电流引起的磁场变化明显不同于恢复相的其他时刻,这可能与高纬较强的亚暴活动有关. 相似文献
2.
对流电场、场向电流和极光区电集流是磁层一电离层耦合的主要物理过程．它们的演化发展时间分别为几分钟至半小时的量级．本文用１００°Ｅ和３００°Ｅ的两个地磁经度链附近各１１个台站的１ｍｉｎ均值地磁Ｈ和Ｚ分量资料,分析了１９９４年４月１６-１７日磁暴期间磁层耦合过程对极光区和中低纬区电离层扰动的地磁特征．强磁暴开始时,台站所处的地方时位置不同,则观测到的电离层和地磁响应也完全不同．这是磁层对流和一、二区场向电流共同作用的结果．一般说,扰时极光区的西向电集流变化更为强烈．随着耦合的发展,极光区范围会向南北扩展,电集流中心带则向低纬侧移动．在中低纬区,二区场向电流的建立能屏蔽一区场向电流所产生的扰动,并引起反向的电流及地磁变化．由此,中低纬区夜间有可能出现短时间的东向电场,又可通过ＥＸＢ的垂直向上漂移作用抬升Ｆ层等离子体,并发生同一经度链附近的多站电离层ｈ＇Ｆ同时突增现象．另一方面,磁赤道附近的台站则更多地受内磁层赤道环电流和电离层赤道电集流的影响． 相似文献
3.
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. 相似文献
4.
为了解极光电集流在sawtooth事件期间的响应情形,本文利用北半球高纬地磁台站的磁场数据,建立了以球元基本电流系反演法求得大尺度电离层水平等效电流系分布的方法,以此研究了2000年9月30日同步轨道LANL卫星观测到的sawtooth事件期间极光电集流的变化.本文将sawtooth注入事件后极区电离层夜侧西向电集流增长的特征,与中低纬地基磁场北向分量正弯扰的特征做比较分析.两者的观测结果都表明在本sawtooth注入事件期间有电流楔的形成,且电流楔约有11 h磁地方时(MLT)的宽度.此外,中低纬磁弯扰达到最大扰动值的时间一般比高纬电集流达到最大扰动值的时间长,说明影响中低纬磁弯扰变化的电流源较丰富. 相似文献
5.
基于Van Allen Probes近三年的EMFISIS仪器波动观测数据,针对内磁层上频带哨声模合声波幅度的全球分布特性对地磁活动水平的依赖性进行了详细的统计分析,着重研究上频带合声波平均场强幅度随磁壳值(L)、磁地方时(MLT)、地磁纬度(MLAT)的分布特征及不同强度区间的合声波的发生概率.结果表明,上频带合声波的平均场强幅度与地磁活动条件密切相关,在强磁扰期,平均幅度可达到40 pT以上.在外辐射带中心区域(L=4~6),上频带合声波的幅度最强;在L~3的区域,上频带磁层合声波没有分布.在夜侧至晨侧(22—09MLT),上频带合声波幅度最强;在下午侧至昏侧(15-19MLT),上频带合声波幅度最弱;日侧(10-14MLT)上频带合声波在不同地磁活动条件下都存在,幅度偏小.上频带合声波主要分布在|MLAT|10°,其中21-09MLT范围内、磁纬位于|MLAT丨5°的平均场强幅度最强,磁扰期间可达约100 pT.另外,统计而言,中等幅度(10~30 pT)的上频带合声波在夜侧至晨侧(23-09MLT)靠近磁赤道区域的发生率最高,可达15%左右.强幅度(30 pT)的上频带合声波普遍分布在夜侧(01-05MLT),发生率最小.本文建立的上频带哨声模合声波的全球分布模型结合已经建立的下频带合声波的全球分布模型,将有助于进一步深入理解该重要磁层等离子体波动对地球等离子体片、辐射带、环电流动力学过程的定量贡献. 相似文献
6.
本文根据OMNI、TC-2卫星、LANL系列卫星、Cluster星簇卫星(C1-C4)以及加拿大的8个中高纬地磁台站的观测数据,研究了2005年8月24日强磁暴(SYM-Hmin~ -179 nT)主相期间的强亚暴(ALmin~ -4046 nT)事件特征.该强磁暴在大振幅(IMF Bz min~ -55.57 nT)、短持续时间(~90 min)的行星际磁场条件下产生,有明显的磁暴急始(SSC),强度较大且持续时间较短.发生在磁暴主相期间的亚暴发展的主要特征如下:亚暴增长相期间,C1-C4卫星先后穿越中心等离子体片;亚暴膨胀相触发后,在近地磁尾(X~-6RE)可观测到磁场偶极化现象;等离子体无色散注入区在亚暴onset开始后迅速沿经向扩展,但被限制在有限的经度范围;磁纬60°附近,Pi2地磁脉动振幅超过了100 nT.膨胀相开始后,在中、高磁纬地磁台站可观测到负湾扰,近地磁尾可观测到Pi2空间脉动,中磁尾区域可观测到尾向流、磁重联以及O+/H+数密度比值在亚暴onset之后增大等现象.分析表明该强磁暴主相期间的强亚暴现象发生时序是自内向外:X~-6RE处TC-2观测到磁场偶极化(~09:42:30 UT),同步轨道卫星LANL1994-084观测到等离子体无色散注入(~09:44:30 UT),X~-17.8RE处C1观测到磁场重联(~09:45:30 UT),由此推断该亚暴事件很可能是近地磁尾不稳定性触发产生,其发生区域距离地球很近. 相似文献
7.
基于Van Allen Probes近三年的EMFISIS仪器波动观测数据,对内磁层下频带哨声模合声波幅度的全球分布特性对地磁活动水平的依赖性进行了详细的统计分析,着重研究下频带合声波平均场强幅度随磁壳值L、磁地方时、地磁纬度的分布特征及不同强度区间的合声波的发生概率.结果表明,下频带合声波的波动强度与地磁活动密切正相关,处于强磁扰期间的合声波具有更大的振幅,其发生率与地磁活动强度具有同样的正相关特性.下频带合声波主要发生于午夜至下午的磁地方时区间,其余的磁地方时时段下频带合声波较弱.赤道面附近的下频带合声波主要分布在夜侧至黎明这一时段内,随着磁纬度的增加逐步向日侧扩展.下频带合声波在午夜侧(21-03 MLT)主要出现在15°的磁纬范围内,在晨侧(03-09 MLT)可以到达15°磁纬甚至更高纬度.下频带合声波主要发生于L=~4.5的附近区域.随着地磁活动的增加,下频带合声波所覆盖的L-shell空间区域增大,趋势为向高、低L值区域同时扩展.建立的下频带哨声合声波的全球分布模型将有助于进一步深入理解该重要磁层波动对辐射带电子的波粒作用散射效应和对辐射带动力学过程的定量贡献. 相似文献
8.
本文综述了不同类型电离层场向电流(亦称为Birkeland电流)及其在地磁扰动(磁暴和亚暴)期间的时空分布特征.首先简述了场向电流近70年的研究历程,总结了各种与太阳风—行星际磁场(interplanetary magnetic field,IMF)、电离层电导率空间分布不均匀相关的1区和2区场向电流,北向、晨昏向IM... 相似文献
9.
本文根据Cluster卫星上的粒子成像质谱仪（RAPID）探测器在穿越地球等离子体片过程中的观测数据,统计研究了等离子体片中能量离子能量密度的空间分布（氢离子能量范围从40keV到1500keV,氦离子和氧离子从10keV到1500keV）,并且给出了离子能量密度在不同地磁活动时期随GSE Z向分布的剖面.研究表明能量离子的能量密度以及能量密度的梯度与地磁活动指数Kp之间存在近似线性的关系.观测结果表明形成这种分布变化的主要原因是在地磁活动期间在电流片附近离子能量密度的增加,特别是其中的重离子成分增加更为显著.本文通过一个简化的电流片模型的数值计算,定性地研究了形成能量离子空间分布的机理.计算表明重离子在电流片中可以获得更多的能量,电流片加速可能是形成能量密度分布变化的一种可能的机制. 相似文献
10.
本文采用一种新的坐标系——耀斑-日球电流片坐标系,对1966—1982年间由耀斑-激波所引起的277个耀斑-地磁扰动事件进行了分析.初步结果是:1.耀斑-地磁扰动事件在该坐标系中相对日球电流片的随机分布呈高斯分布,极大值在电流片附近;2.当地球和耀斑位于日球电流片同侧时,地磁扰动事件频次远高于异侧;3.地磁扰动强弱在该坐标系中的分布,亦呈现了同侧高于异侧,且极大值多在日球电流片附近;4.耀斑-激波能流密度ρ_2V_2~3及其跃变量ρ_2V_2~3-ρ_1V_1~3在该坐标系中具有十分类似于相应磁扰水平的分布,其离散程度后者略大于前者. 根据本文的结果可以看出,对耀斑-地磁扰动研究来说,近太阳日球电流片的存在是一个重要的特征面,它对耀斑-地磁扰动的产生和强弱水平有重要影响,使太阳耀斑活动与地磁活动效应之间的对应关系变得复杂化了. 相似文献
11.
O.M. Pirog N.M. Polekh E.B. Romanova A.V. Tashchilin G.A. Zherebtsov 《Journal of Atmospheric and Solar》2009,71(1):49-60
Research results concerning the main ionospheric trough (MIT) in the afternoon sector are present. Data are used from the meridional chain of stations located in the East Asian region. The analysis of ionospheric storms with different intensities reveals that the depletion in the F2 layer ionization in the afternoon/evening sector can be observed in the subauroral latitudes in the storm recovery phase predominantly during equinoxes and is associated with the formation of the MIT equatorward wall. Model calculations of the evening trough show that its location coincides with the belt of westward drift in the geomagnetic latitudes 55–65° at 13–17 MLT. Hence the simulated results support the assumption that the narrow and deep trough in the afternoon sector is formed by the westward drift with high velocities (～700 m/s). the drift transports the low-density plasma from the night side. The eastward drift with high velocities (～1000–1200 m/s) transports the low-density plasma from the night to morning side forming a trough in the morning sector. 相似文献
12.
The level of wave geomagnetic activity in the morning, afternoon, and nighttime sectors during strong magnetic storms with Dst varying from ?100 to ?150 nT has been statistically studied based on a new ULF wave index. It has been found out that the intensity of geomagnetic pulsations at frequencies of 2–7 mHz during the magnetic storm initial phase is maximal in the morning and nighttime sectors at polar and auroral latitudes, respectively. During the magnetic storm main phase, wave activity is maximal in the morning sector of the auroral zone, and the pulsation intensity in the nighttime sector is twice as low as in the morning sector. It has been indicated that geomagnetic pulsations excited after substorms mainly contribute to a morning wave disturbance during the magnetic storm main phase. During the storm recovery phase, wave activity develops in the morning and nighttime sectors of the auroral zone; in this case nighttime activity is also observed in the subauroral zone. 相似文献
13.
Using data from ground-based ionospheric sounding stations, we studied the morphologic features of the disturbance pattern
of the electron concentration at the midlatitude F2-layer maximum (NmF2) in the period of a magnetic superstorm, which began on July 15, 2000. In the Southern (winter) Hemisphere in the latitudinal
sector, where the main storm phase began after sunrise, negative NmF disturbances were observed at quite high midlatitudes both day and night; whereas large positive NmF disturbances took place at lower midlatitudes in nighttime hours. In the Northern (summer) Hemisphere at latitudes where
the main storm phase occurred in the local evening, only long-term negative disturbances were observed in daytime and nighttime
hours; whereas at latitudes where the main storm phase began in the afternoon, NmF2 experienced both negative and positive disturbances. Based on analysis of data of KOMPSAT-l, ROCSAT-1, DMSP F13, F14, and
F15 satellites, we present clear arguments for the viewpoint of many authors that it is just the enhancement of the eastward
electric field in the evening sector that led to formation of the large-scale trough in the nighttime low-latitude upper ionosphere.
This field enhancement was due to penetration of the magnetospheric electric field to low latitudes, not to the dynamo action
of the disturbed neutral wind. It is also shown that, due to equatorward expansion of the magnetospheric convection system
during the main storm phase, the plasmapause and the main ionospheric trough were shifted to a magnetic latitude of 40° (L ∼ 1.7). 相似文献
14.
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. 相似文献
15.
基于CHAMP卫星资料,分析了2002—2008年267个磁暴期间400km高度大气密度变化对季节、地方时与区域的依赖以及时延的统计学特征,得到暴时大气密度变化的一些新特点,主要结论如下:1)两半球大气密度绝对变化(δρa)结果在不同强度磁暴、不同地方时不同.受较强的焦耳加热和背景中性风共同作用,在北半球夏季,中等磁暴过程中夜侧和大磁暴中,夏半球的δρa强于冬半球;由于夏季半球盛行风环流造成的扰动传播速度快,北半球夏季日侧30°附近大气,北(夏)半球到达峰值的时间早于南(冬)半球.而可能受半球不对称背景磁场强度所导致的热层能量输送率影响,北半球夏季强磁暴和中磁暴个例的日侧,南半球δρa强于北半球;春秋季个例中日侧30°附近大气,北半球先于南半球1~2h达到峰值.2)受叠加在背景环流上的暴时经向环流影响,春秋季暴时赤道大气密度达到峰值的时间最短,日/夜侧大气分别在Dstmin后1h和2h达到峰值.至点附近夜侧赤道大气达到峰值时间一致,为Dstmin后3h;不同季节日侧结果不同,在北半球冬季时赤道地区经过更长的时间达到峰值.3)日侧赤道峰值时间距离高纬度峰值时间不受季节影响,为3h左右.在春秋季和北半球冬季夜侧,赤道大气密度先于高纬度达到峰值,且不同纬度大气密度的峰值几乎无差别,表明此时低纬度存在其他加热源起着重要作用. 相似文献
16.
The dynamics of the auroral precipitation boundaries in the daytime (0900–1200 MLT) and nighttime (2100–2400 MLT) sectors during two strong magnetic storms of February 8–9, 1986, and March 13–14, 1989, with a Dst value at a maximum of approximately ?300 and ?600 nT, respectively, are studied using the DMSP satellite data. It is shown that, during the main phase of a storm, a shift to lower latitudes of the poleward and equator ward boundaries of the daytime precipitation is observed. In the nighttime sector, the equatorward boundary of the precipitation also shifts to lower latitudes, whereas the position of the poleward boundary depends weakly on the magnetic activity level even in the periods of very strong magnetic disturbances. The increase in the polar cap area occurs mainly due to the equatorward shift of the daytime precipitation. A high correlation degree between the equatorward shift of the poleward boundary of the daytime precipitation and the position of the equatorward boundary of the precipitation at the nighttime side of the Earth is demonstrated. The analysis of the events shows that (1) the magnetic activity level in the nighttime sector of the auroral zone influences considerably the position of the daytime precipitation boundaries during magnetic storms and that (2) the ring current inputs considerably into the value of the Dst variations. 相似文献
17.
Biqiang Zhao Weixing Wan Libo Liu K. Igarashi K. Yumoto Baiqi Ning 《Journal of Atmospheric and Solar》2009,71(1):88-100
This paper presents an investigation of geomagnetic storm effects in the equatorial and middle-low latitude F-region in the West Pacific sector during the intense geomagnetic storm on 13–17 April, 2006. The event, preceded by a minor storm, started at 2130 UT on April 13 while interplanetary magnetic field (IMF) Bz component was ready to turn southward. From 14–17 the ionosphere was characterized by a large scale enhancement in critical frequency, foF2 (4～6 MHz) and total electron content (TEC) (～30TECU, 1TECU=1×1016el/m2) followed by a long-duration negative phase observed through the simultaneous ionospheric sounding measurements from 14 stations and GPS network along the meridian 120°E. A periodic wave structure, known as traveling ionospheric disturbances (TIDs) was observed in the morning sector during the initial phase of the storm which should be associated with the impulsive magnetospheric energy injection to the auroral. In the afternoon and nighttime, the positive phase should be caused by the combination of equatorward winds and disturbed electric fields verified through the equatorial F-layer peak height variation and modeled upward drift of Fejer and Scherliess [1997. Empirical models of storm time equatorial electric fields. Journal of Geophysical Research 102, 24,047–24,056]. It is shown that the large positive storm effect was more pronounced in the Southern Hemisphere during the morning-noon sector on April 15 and negative phase reached to lower magnetic latitudes in the Northern Hemisphere which may be related to the asymmetry of the thermospheric condition during the storm. 相似文献
18.
A very strong magnetic storm of May 15, 2005, was caused by an interplanetary magnetic cloud that approached the Earths’ orbit. The sheath region of this cloud was characterized by a high solar wind density (～25–30 cm?3) and velocity (～850 km/s) and strong variations (to ～20 nT) in the interplanetary magnetic field (IMF). It has been indicated that an atypical bay-like geomagnetic disturbance was observed during the initial phase of this storm in a large longitudinal region at high latitudes: from the morning to evening sectors of the geomagnetic local time. Increasing in amplitude, the magnetic bay rapidly propagated to the polar cap latitudes up to the geomagnetic pole. An analysis of the global space-temporal dynamics of geomagnetic pulsations in the frequency band 1–6 mHz indicated that most intense oscillations were observed in the morning sector in the region of the equivalent ionospheric current at latitudes of about 72°–76°. The wavelet structure of magnetic pulsations in the polar cap and fluctuations in IMF was generally similar to the maximum at frequencies lower than 4 mHz. This can indicate that waves directly penetrated into the polar cap from the solar wind. 相似文献
19.
N. G. Kleimenova E. E. Antonova O. V. Kozyreva L. M. Malysheva T. A. Kornilova I. A. Kornilov 《Geomagnetism and Aeronomy》2012,52(6):746-754
A new type of high-latitude magnetic bays is revealed at geomagnetic latitudes higher than 71°, called ??polar substorms.?? It is shown that polar substorms differ from both classical substorms and high-latitude geomagnetic disturbances of the type of polar boundary intensifications (PBIs). While classical substorms start at latitudes below 67° and then expand poleward, polar substorms start almost simultaneously in the evening-night polar region of the oval. In contrast to PBIs, accompanied by auroral streamers expanding southward, polar substorms are accompanied by auroral arcs quickly traveling northward. It is shown that polar substorms are observed before midnight (20?C22 MLT) under weak geomagnetic activity (Kp ?? 2) during the late recovery phase of a magnetic storm. It is shown that a typical feature of polar substorms is the simultaneous excitation of highly intensive Pi2 and Pi3 geomagnetic pulsations at high latitudes, which exceed the typical amplitude of these pulsations at auroral latitudes by more than an order of magnitude. The duration of pulsations is determined by the substorm duration, and their amplitude decreases sharply at geomagnetic latitudes below ??71°. It is suggested that pulsations reflect fluctuations in ionospheric currents connected with polar substorms. 相似文献