Pc2 EMIC waves generated high off the equator in the dayside outer magnetosphere
Pc2 EMIC waves generated high off the equator in the dayside outer magnetosphere
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DOI：
10.1029/2012gl053082
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发表时间：
2012-09
影响因子：
5.2
通讯作者：
Y. Liu;B. J. Fraser;F. Menk
中科院分区：
文献类型：
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作者：
Y. Liu;B. J. Fraser;F. Menk
一般认为电磁离子回旋波（EMIC）产生于赤道附近，并向两半球的高纬电离层传播。本文描述了一个由四颗星团卫星在赤道以北13 °~20 °磁纬，穿过当地磁中午附近高纬尖区，从外磁层L_13向日穿越到磁层顶，在He~+回旋频率以上的Pc~2（0.1-0.2Hz）频段上观测到的一个长时间EMIC波事件。波包能量主要沿着地磁场方向传播，证实这是一个行进的EMIC波，而不是环向场线共振。能量包在交替方向上传播，而不是从赤道单向传播，这意味着波源位于远离赤道的高纬度地区，B场的最小值位于该地区。CIS ‐ CODIF H+离子数据提供的证据表明，波是通过离子回旋不稳定性局部产生的。我们认为，赤道外的最小磁场区域可能是这些波在外磁层中的重要源区。
It is generally accepted that electromagnetic ion cyclotron (EMIC) waves are generated around the equatorial regions and propagate toward the high latitude ionospheres in both hemispheres. Here we describe a prolonged EMIC wave event in the Pc2 (0.1–0.2 Hz) frequency band above the He+ cyclotron frequency detected by the four Cluster satellites as they traversed sunward from L∼ 13 in the outer magnetosphere to the magnetopause, over 13°–20° magnetic latitude north of the equator and across the high latitude cusp region near local magnetic noon. Wave packet energy propagated dominantly along the geomagnetic field direction, confirming this was a traveling EMIC wave rather than a toroidal field line resonance. The energy packets propagated in alternating directions rather than uni‐directionally from the equator, implying the wave source was located in a high latitude region away from the equator, where a minimum in the B field is located. The CIS‐CODIF H+ion data provided evidence that the waves were generated locally via the ion cyclotron instability. We believe the off‐equatorial minimum magnetic field regions may be important source regions for these waves in the outer magnetosphere.