偶极化锋面在地球磁尾的能通量传输中有着重要的作用，也因其与磁尾中的电流体系的密切关系而备受人们关注，成为近来空间天气领域十分热门的研究对象。偶极化锋面最明显的观测特征是磁场Bz迅速的增强，在其前端，往往可以观测到一个磁场Bz的降低区域(Bz dip)。有理论研究认为，这一现象是由于偶极化锋面对其前端离子的反射形成的次生电流所造成的，但仍然缺乏观测上的证据。在本工作中，我们利用THEMIS卫星的观测数据，分析发现磁场dip的深度明显受到偶极化锋面传播速度和背景等离子体片密度的影响，从统计的角度印证了偶极化锋面对背景离子的反射能重塑锋面附近的磁场位型。
该成果发表在 Geophys. Res. Lett. (GRL)上。文章链接http://onlinelibrary.wiley.com/doi/10.1002/2015GL064369/full
文章作者为：潘东晓，周煦之，史全岐，刘江，Vassilis Angelopoulos，Andrei Runov，宗秋刚和傅绥燕。
研究工作得到国家自然科学基金的支持。
Pan, D.-X., X.-Z. Zhou, Q.-Q. Shi, J. Liu, V. Angelopoulos, A. Runov, Q.-G. Zong, and S.-Y. Fu (2015), On the generation of magnetic dips ahead of advancing dipolarization fronts, Geophys. Res. Lett. , 42 , doi:10.1002/2015GL064369.
On the generation of magnetic dips ahead of advancing dipolarization fronts
Dong-Xiao Pan1, Xu-Zhi Zhou1, Quan-Qi Shi2, Jiang Liu3, Vassilis Angelopoulos3, Andrei Runov3,
Qiu-Gang Zong1, and Sui-Yan Fu1
1 School of Earth and Space Sciences, Peking University, Beijing, China
2 School of Space Sciences and Physics, Shandong University at Weihai, Weihai, China
3 Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California, USA
Dipolarizing flux bundles (DFBs) transport magnetic flux to the inner and dayside magnetosphere, heat the plasma sheet, and provide a seed population to the radiation belt. The magnetic perturbation ahead of them, often referred to as a dipolarization front (DF), is asymmetric with a small Bz dip followed by a sharp Bz enhancement. The Bz dip is thought to be generated from dawnward currents carried by DF-reflected ions; after reflection, these earthward-moving ions gyrate clockwise and contribute to dawnward diamagnetic currents ahead of the front. Using observations of hundreds of DFs, we investigate this hypothesis. We find that the depth of the Bz dip as a function of the front azimuth depends on DF propagation speed and ambient plasma density. These statistical signatures support the hypothesis that the Bz dip is caused by ion reflection, and suggest that secondary currents carried by these reflected ions can reshape the front significantly.
