高速流前端磁场<em>B</em><sub>z</sub>分量的变化

盛程; 傅绥燕; 郑昊; 白曦; 杨彪; 王永福

doi:10.11728/cjss2012.06.793

高速流前端磁场B_z分量的变化

doi: 10.11728/cjss2012.06.793

北京大学地球与空间科学学院北京 100871

基金项目: 国家自然科学基金项目资助(40874086, 41031065)

详细信息

中图分类号: P353
计量
- 文章访问数: 2358
- HTML全文浏览量: 29
- PDF下载量: 1041
- 被引次数: 0
出版历程
- 收稿日期: 2011-05-26
- 修回日期: 2012-04-28
- 刊出日期: 2012-11-15

Variation of the B_z Component of Magnetic Field During the Front of Bursty Bulk Flows

School of Earth and Space Science, Peking University, Beijing 100871

摘要

摘要: 等离子体片高速流在磁层活动中起着重要作用, 其形成机制以及与背景等离子体的相互作用日益引起关注. 本文利用搭载于Cluster四颗卫星上的磁场和等离子体观测仪器, 对2001和2002两年发生在磁尾等离子体片中高速流事件期间的磁场变化进行了统计研究. 结果表明, 在高速流前端, 伴随着等离子体整体速度的增加, 绝大多数高速流前端磁场的B_z分量经常出现先短暂减小然后剧烈增大的现象, 符合以往利用Geotail卫星观测数据获得的统计特性. 然而个例研究发现B_z的下降与上升常常是不对称的, 且B_z分量下降的程度并不是总能达到反向的程度, 说明这种变化特征并不一定是存在磁结构的表现. 我们认为更多时候这种磁场的变化特征是高速流挤压背景等离子体磁场造成的, 是相互作用的结果. 当偶极化锋面形成后, 由类似间断面的磁场界面反射的热离子产生抗磁效应, 可能对B_z下降形成部分贡献, 而B_z增加则是高速流携带磁通量堆积的效果.
- 等离子体片 /
- 高速流 /
- 背景等离子体 /
- 磁结构
Abstract: Bursty Bulk Flows (BBFs) play an important role in the magnetotail activites. The formation mechanism of BBFs and the interaction between BBFs and the ambient plasma have become important research subjects recently. Based on the observations made by Cluster during the periods from July to October 2001 and 2002, the variations of magnetic field during the passage of BBFs are statistically analyzed. Superposed epoch analyses show that there is a sharp change in the B_z component as the bulk speed of the flow begins to increase at the front of BBFs: a sharp increase preceded by a transient decrease. This signature in B_z component was found in most of the BBFs events observed by Cluster, which is generally agreed with the result reported based on Geotail observations. However, the change of B_z component is not always symmetry, and the decease of B_z is usually not strong enough to lead to a negative value. This implied that magnetic structure does not always occur together with BBFs. The interaction between BBFs and ambient plasma is responsible for the change in B_z. After the dipolarization front is formed, the diamagnetic effect due to the hot ions bouncing back from the boundary might contribute to the decrease in B_z. The pile-up of the magnetic flux carried by BBFs may be the reason for the increase.
- Plasma sheet /
- Bursty bulk flows /
- Ambient plasma /
- Magnetic structure

HTML全文

参考文献(26)

[1]	Angelopoulos V, Baumjohann W, Kennel C F, et al. Bursty bulk flows in the inner central plasma sheet[J]. J. Geophys. Res., 1992, 97:4027-4039
[2]	Angelopoulos V, Coroniti F V, Kennel C F, et al. Multipoint analysis of a bursty bulk flow event on April 11, 1985[J]. J. Geophys. Res., 1996, 101:4967-4989
[3]	Ohtani S, Shay M A, Mukai T. Temporal structure of the fast convective flow in the plasma sheet: Comparison between observations and two-fluid simulation[J]. J. Geophys. Res., 2004, 109, A03210, doi:10.1029/ 2003JA010002
[4]	Slavin J A, Lepping R P, Gjerloev J, et al. Geotail observations of magnetic flux ropes in the plasma sheet[J]. J. Geophys. Res., 108(A1), 1015, doi:10.1029/ 2002JA009557, 2003
[5]	Runov A, Angelopoulos V, Sitnov M I, et al. THEMIS observations of an earthward- propagating depolarization front[J]. Geophys. Res. Lett., 36, L14106, doi:10.1029/ 2009GL038980
[6]	Runov A, Angelopoulos V, Sitnov M, et al. Dipolarization fronts in the magnetotail plasma sheet[J]. Planet. Space Sci., 2010, doi: 10.1016/j.pss.2010.06.006
[7]	Sormakov D A, Sergeev V A. Topology of magnetic flux ropes in the magnetospheric plasma sheet as measured by the Geotail spacecraft[J]. Cosmic Res., 2008, 46(5):387-391
[8]	Cao J B, Ma Y D, Parks G, et al. Joint observations by Cluster satellites of bursty bulk flows in the magnetotail[J]. J. Geophys. Res., 2006, 111, A04206, doi: 10.1029/2005JA011322
[9]	Shue J H, Ieda A, Lui A T Y, et al. Two classes of earthward fast flows in the plasma sheet[J]. J. Geophys. Res., 113, A02205, doi: 10.1029/2007JA012456
[10]	Ma Y D, Cao J B, Nakamura R, et al. Statistical analysis of earthward flow bursts in the inner plasma sheet during substorms[J]. J. Geophys. Res., 114, A07215, doi: 10.1029/2009JA014275
[11]	Panov E V, Nakamura R, Baumijohann W, et al. Multiple overshoot and rebound of a bursty bulk flow[J]. Geophys. Res. Lett., 2010, 37, L08103, doi: 10.1029/2009GL041971
[12]	Ma Y D, Cao J B, Reme H, et al. The radial evolution of earthward BBFs during substorm[J]. Sci China Earth Sci., 2010, 53:1542-1551, doi: 10.1007/s11430-010-4040-x
[13]	Reme H, Aoustin C, et al. First multisapacecraft ion measurements in and near the Earth's magnetosphere with the identical Cluster Ion Spectrometry (CIS) experiment[J]. Ann. Geophys., 2001, 19:1303-1354
[14]	Wilken B, Guttler W, Korth A, et al. RAPID the imaging energetic particle spectrometer on Cluster[J]. Space Sci. Rev., 1997, 79:399-473
[15]	Balogh A H, Carr C M, Acuna M H, et al. The cluster magnetic field investigation: Overview of in-flight performance and initial results[J]. Ann. Geophys., 2001, 19:1207-1217
[16]	Zhou X Z, Angelopoulos E V, Sergeev V, Runov A. Accelerated ions ahead of Earthward-propagating dipolarization fronts[J]. J. Geophys. Res., 2010, 115, A00103, doi: 10.1029/2010JA015481
[17]	Zhou X Z, Angelopoulos V, Sergeev V, Runov A. On the nature of precursor flows upstream of advancing dipolarization fronts[J]. J. Geophys. Res., 2011, 116, A03222, doi: 10.1029/2010JA016165
[18]	Nakamura R, Baumihohann W, Klecher B, et al. Motion of the dipolarization front during a flow burst event observed by Cluster[J]. Geophys. Res. Lett., 2002, 29(20):1942
[19]	Nakamura R, Baumihohann W, Zhang T L, et al. Cluster and Double Star observations of dipolarization[J]. Ann. Geophys., 2005, 23:2915-2920
[20]	Shiokawa K, Miyashita Y, Shinohara I, Matsuoka A. Decrease in B_z prior to the dipolarization in the near-Earth plasma sheet[J]. J. Geophys. Res., 2005, 110, A09219, doi: 10.1029/2005JA011144
[21]	Henderson P D, Owen C J, Alexeev I V, et al. Cluster observations of flux rope structures in the near-tail[J]. Ann. Geophys., 2006, 24:651-666
[22]	Sergeev V, Angelopoulos V, Apatenkov S, et al. Kinetic structure of the sharp injection/dipolarization front in the flow-braking region[J]. Geophys. Res. Lett., 36, L21105, doi: 10.1029/2009GL040658
[23]	Zhou M, Ashour-Abdalla M, Deng X, et al. THEMIS observation of multiple dipolarization fronts and associated wave characteristics in the near-Earth magnetotail[J]. Geophys. Res. Lett., 2009, 36, L20107, doi: 10.1029/2009GL040663
[24]	Deng X, Ashour-Abdalla M, Zhou M, et al. Wave and particle characteristics of earthward electron injections associated with dipolarization fronts[J]. J. Geophys. Res., 2010, 115, A09225, doi: 10.1029/2009JA015107
[25]	Zhang X J, Angelopoulos V, Runov A, et al. Current carriers near dipolarization fronts in the magnetotail: A THEMIS event study[J]. J. Geophys. Res., 2011, 116, A00I20, doi: 10.1029/2010JA015885
[26]	Fu H S, Khotyaintsev Y V, Andre M, et al. Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts[J]. Geophys. Res. Lett., 2011, 38, L16104, doi: 10.1029/2011GL048528