共查询到16条相似文献，搜索用时 187 毫秒
1.
卫星观测证实了磁尾等离子体团与亚暴活动的相关性,除了具有北-南双极特征的尾向传播等离子体团外,还发现地向传播等离子体团,它们表现为南-北双极中性片事件和南-北双极瓣区讯号. 资料分析表明:南-北双极讯号的出现几率远低于北-南双极讯号,并且南-北双极事件主要发生于行星际磁场北向和地磁宁静条件,它们往往与小的孤立的地磁亚暴相关. 本文根据地磁宁静时期(IMF Bz北向且By≥Bz)越尾电场Ey分量的分布特点,对地向传播等离子体团作模拟研究. 两类算例的数值结果展示了通量绳磁结构及具有复杂闭合磁力线位形的等离子体团的基本特征,上述特征与尾向传播的等离子体团类似,与IMP 8卫星关于地向传播南-北中性片事件的观测特征大致相符. 数值结果还展示了与Schindler示意图相类似的磁力线拓扑位形,在一定程度上为南-北事件出现几率低作出了解释;并且揭示了磁尾中性片内越尾磁场分量By对磁重联发展的抑制作用. 本文的模拟研究说明:无论磁尾处于活动时期(IMF Bz为南向),还是宁静时期(IMF Bz为北向且By≥Bz),磁场重联均是磁尾等离子体加速和加热的通用机制. 相似文献
2.
利用全球磁流体力学(MHD)的模拟结果,研究了太阳风压力系数与上游太阳风参数和日下点磁层顶张角的相关性.在识别出日下点附近磁层顶位置后,通过拟合得到日下点附近的磁层顶张角.在考虑上游太阳风中的磁压和热压以及磁层顶外侧的太阳风动压的情况下,计算了太阳风压力系数.通过分析行星际磁场不同方向时太阳风动压在日地连线上与磁压和热压的转化关系,详细研究了太阳风参数和日下点磁层顶张角对太阳风压力系数的影响,得到以下相关结论:(1) 在北向行星际磁场较大(Bz≥5 nT)时,磁层顶外侧磁压占主导,南向行星际磁场时磁层顶外侧热压占主导;(2) 太阳风压力系数随着行星际磁场的增大而增大,随着行星际磁场时钟角的增大而减小;并且在行星际磁场大小和其他太阳风条件相同时,北向行星际磁场时的太阳风压力系数要大于南向行星际磁场时的;北向行星际磁场时,太阳风压力系数随着太阳风动压的增大而减小,南向行星际磁场时,太阳风压力系数随着太阳风动压的增大而增大;以上结论是对观测结果的扩展;(3) 最后,我们还发现太阳风压力系数随着日下点磁层顶张角的增大而增大. 相似文献
3.
等离子体系统中存在两个或多个电流片时，电流片中发生的不稳定性可能会相互作用．行星际磁场北向时，背阳面碰层顶电流片与磁尾等离子体片之间可能发生相互作用，高纬边界层强烈的流场剪切可能促进磁场重联，产生磁层亚暴．本文运用二维可压缩磁流体模拟研究具有强流场剪切的多个电流片系统中磁场重联的演化．结果表明，Kelvin－Helmholtz不稳定性使多电流片系统的磁场重联过程明显加快；相邻电流片之间的距离越近，两者相互作用越强，重联增长率越大；在三电流片系统中，超Alfven速度强流场导致外侧两个电流片中出现强烈的磁场重联，并引发中心电流片的磁场重联．行星际磁场北向时，也可能发生磁层亚暴． 相似文献
4.
本文利用THEMIS卫星的磁场数据和等离子体观测数据,统计分析地球磁尾等离子体片区域线性磁洞的发生率、时空尺度、分布特征、和发生率与地磁AE指数的相关性.分析结果表明磁尾等离子体片区域的磁洞的时间尺度为几秒到几十秒,空间尺度小于当地的质子回旋半径.通过磁洞在空间的位置分布和卫星数据在空间的数据采样分布的对比,我们发现线性磁洞在等离子体片内经常发生,然而在磁尾等离子体片中的发生率要小于太阳风中磁洞的发生率.本文最后统计分析了磁洞发生和AE指数的相关性,结果表明磁洞可能与地磁活动有关系. 相似文献
5.
《中国科学:地球科学》2015,(12)
使用2007~2011年THEMIS卫星数据,对位于地球磁尾(|YGSM|13RE,|ZGSM|5RE,–30REXGSM–6RE)等离子体片内的高速流及背景的等离子体特性和它们与太阳风参数之间的联系进行了统计研究.我们发现,距离地球越近,高速流温度的增加相较于其背景要更强一些;高速流与背景的离子数密度比值和离子温度比值也都有所升高;而我们的统计进一步表明,高速流密度与其发生前2 h的太阳风密度相关性最高,背景密度与其观测时刻前3.5 h的太阳风密度相关性最高,且二者的归一化密度(密度与太阳风密度之比)均与其前3 h的行星际磁场θ角(θ=arctan(Bz/sqrt(Bx2+By2)))相关性程度最大.行星际磁场越倾向于北向,高速流归一化密度越大,与磁尾背景等离子体的性质相似. 相似文献
6.
2004年7月14日TC-1卫星在近地磁尾(-9.3Re,-5.4Re,1.2Re)附近观测到了伴随有持续尾向流的等离体片变薄和偶极化过程.尾向流持续时间为32分钟.偶极化过程中磁场By分量没有明显变化.在偶极化过程发生两分钟之后,地面台站观测到的Pi2脉动.ACE卫星的观测表明行星际磁场有弱的南向行星际磁场（-2nT）,持续时间约55分钟.Imagine卫星在电离层区域没有观测到极光出现.和伴随有极光增亮的亚暴过程相比,南向行星际磁场明显较弱,且持续时间短.TC-1卫星和ACE卫星的联合观测表明尾部释能有大有小,并非达到某值才能发生.但能量小时,不能够引起极光亚暴.其次南向行星际磁场有可能与近地磁尾尾向流有密切关系. 相似文献
7.
利用Cluster卫星数据,选取2001—2010年期间的616个极尖区穿越事件,研究了行星际磁场（IMF）的大小和方向对极尖区位形的影响.结果表明：当Bz为北向时,随着Bx负向的增大,极尖区的磁不变纬度向高纬方向（极区）移动;当Bz为南向时,随着Bx负向增大,极尖区的磁不变纬度略微向低纬度方向（赤道）移动.Bx正向增大时,极尖区并没有明显移动.Bx对极尖区影响在南半球较为显著,在北半球没有明显规律性变化.此外,随着行星际磁场锥角的增大（>90°）,极尖区也随之向高纬移动.当Bz南向时,随着By的负向增大,极尖区在北半球向晨侧移动,在南半球向昏侧移动.而当Bz南向增加时,南北半球两个极尖区的磁不变纬度都朝赤道方向移动;但北向Bz时几乎没有移动. 相似文献
8.
磁尾电流片在磁尾动力学过程中起着重要作用.卫星观测表明磁尾电流片经常处于拍动状态.但磁尾电流片拍动的特性和产生机制至今仍然没有被完全弄清楚.本文主要利用欧洲空间局Cluster卫星数据,研究一个伴随高速离子流的电流片拍动事件.该电流片拍动事件具有很强的周期性.拍动的周期约是2min,磁场振荡幅度约为20nT.能量电子和离子的通量具有周期性增强和减弱的特征.电流密度X和Y分量也具有周期性的振荡,并且振荡周期与磁场振荡周期一致.通过对粒子流速矢量与电流矢量的分析,发现粒子运动具有涡旋的特征.因此可以推断,该磁尾电流片的拍动不是由磁尾等离子体片高速流产生的,而是与局地等离子体不稳定性有关. 相似文献
9.
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
10.
11.
《Journal of Atmospheric and Solar》2008,70(17):2132-2143
We study the influence of the interplanetary magnetic field (IMF) and convection electric field on the rate and destination of polar wind and other thermal (low-energy) ion outflows, and its resulting effects on magnetosphere–ionosphere coupling, using single-particle trajectory simulations in conjunction with ion velocity distribution measurements on Akebono and IMF and ionospheric convection data. We find that the ions preferentially feed the dusk sector of the plasma sheet when the IMF is duskward (By>0), and are more evenly distributed in the plasma sheet when the IMF is dawnward. The flow of oxygen ions originating from the noon or dusk sectors of the polar cap has a higher probability of reaching the magnetosphere and beyond compared with that from the dawn or midnight sectors, due to the increased centrifugal acceleration associated with the larger magnetic field curvature near noon and the increased convection electric field in the dusk sector. The flow is enhanced and confined to lower L-shells at times of strongly southward IMF, compared with that at times of northward IMF. The outflow rate to both the plasma sheet and the magnetotail correlates strongly with the ion temperature. As a result, the IMF and the convection electric fields affect both the overall magnitude and the detailed distribution of mass transfer from the ionosphere to the magnetosphere in magnetosphere–ionosphere coupling. 相似文献
12.
Characteristics of isolated substorms selected by variations in the 1-min values of the AL index are analyzed. The substorms were divided into several types with respect to the behavior of the Bz component of the interplanetary magnetic field (IMF) during the expansion phase. The probability of observations of substorms associated with the northward turn of the Bz component of IMF was ~19%, while the substorms taking place at Bz < 0 were observed in 53% of cases. A substantial number of events in which no substorm magnetic activity was observed in the auroral zone after a long (>30 min) period of the southward IMF and a following sharp turn of the Bz component of IMF before the north was detected. The data suggest that a northward IMF turn is neither a necessary nor sufficient condition for generating substorms. It has been shown for substorms of the both types that the average duration of the southward IMF to moment T 0 and the average intensity of the magnetic perturbation in the maximum are approximately the same and amount to ~80 min and–650 nT, respectively. However, for substorms at Bz < 0, their mean duration, including the expansive and recovery phases, is on average 30 min longer than that at a northward turn of IMF. Correlations between the loading–unloading processes in the magnetosphere in the periods of magnetospheric substorms were investigated with different functions that determine the efficiency of the energy transfer from the solar wind to the magnetosphere. It has been shown that the highest correlation coefficient (r = 0.84) is observed when the function suggested by Newell et al. (2007) is used. It has been detected that a simple function VB S yields a high correlation coefficient (r = 0.75). 相似文献
13.
IMF-associated cloudiness above near-pole station Vostok: Impact on wind regime in winter Antarctica
《Journal of Atmospheric and Solar》2008,70(10):1289-1300
Changes in the cloudiness above the Antarctic station Vostok during the winter season were examined in relation to strong disturbances in the interplanetary magnetic field (IMF). A reliable relationship between cloud formation and IMF has been found: cloudiness increased under the influence of a strong southward IMF and decreased under the northward IMF. The surface temperature at Vostok station, which is derivative of the constant radiation cooling of air situated at the ice sheet and adiabatic warming of the air masses, incoming into the central Antarctica from the middle and upper troposphere, is enhanced or reduced. Quite opposite regularity in the temperature changes is typical of altitudes higher than the suggested cloud layer position (5–8 km). The processes occurring on the Antarctic ridge leads to anomalous winds at the ice dome and decay of the circumpolar vortex at the periphery of the Antarctic continent. As a result, the surface easterlies at the coast stations are replaced by southerlies, and the cold air masses flow from Antarctica out over the Southern Ocean. 相似文献
14.
综合分析EISCAT雷达与卫星当地测量数据,并利用磁层磁场模式对磁力线进行追踪,研究了发生在极光椭圆朝极盖边界附近电离层中,一例反常的背离太阳流动的强等离子体对流事件,及相关的太阳风-磁层-电离层耦合过程.结果表明,磁暴期间IMFBz指向南时观测到这一反常高速对流,及其相应的等离子体性态特征,很可能是向阳侧磁层顶磁重联过程在电离层中的印记. 相似文献
15.
L.R. Lyons S. Zou C.J. Heinselman M.J. Nicolls P.C. Anderson 《Journal of Atmospheric and Solar》2009,71(6-7):717-728
The plasma sheet moves earthward (equatorward in the ionosphere) after enhancements in convection, and the electrodynamics of this response is strongly influenced by Region 2 magnetosphere–ionosphere coupling. We have used Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) observations associated with two relatively abrupt southward turnings of the IMF to provide an initial evaluation of aspects of this response. The observations show that strong westward sub-auroral polarization streams (SAPS) flow regions moved equatorward as the plasma sheet electron precipitation (the diffuse aurora) penetrated equatorward following the IMF southward turnings. Consistent with our identification of these flows as SAPS, concurrent DMSP particle precipitation measurements show the equatorial boundary of ion precipitation equatorward of the electron precipitation boundary and that westward flows lie within the low-conductivity region between the two boundaries where the plasma sheet ion pressure gradient is expected to drive downward R2 currents. Evidence for these downward currents is seen in the DMSP magnetometer observations. Preliminary examination indicates that the SAPS response seen in the examples presented here may be common. However, detailed analysis will be required for many more events to reliably determine if this is the case. If so, it would imply that SAPS are frequently an important aspect of the inner magnetospheric electric field distribution, and that they are critical for understanding the response of the magnetosphere–ionosphere system to enhancements in convection, including understanding the earthward penetration of the plasma sheet. This earthward penetration is critical to geomagnetic disturbance phenomena such as the substorm growth phase and the formation of the stormtime ring current. Additionally, for one example, a prompt electric field response to the IMF southward turnings is seen within the inner plasma sheet. 相似文献
16.
The dynamics of auroral arcs, observed in the prenoon sector during the 2-h period, has been studied in the context of ionospheric convection. The appearance of an isolated arc, the poleward drift velocity of which pronouncedly exceeded the plasma drift velocity, accompanied the IMF impulse and could result from the Alfvén resonance oscillations of the magnetosphere. Arcs that appeared after the northward turning of the IMF vertical component drifted poleward at a velocity close to the convection velocity. The mechanism of arc generation is related to the flute instability which develops in the region of the large-scale field-aligned current. Flute instability indications are found out in the POLAR satellite data. The study confirms the previously proposed classification criterion for dayside arcs with the source on closed field lines, based on the character of arc drift as compared to convection. 相似文献