Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements
Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements
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基于 IMAGE FUV 和 EISCAT 测量的磁尾重连率估计
DOI：
10.5194/angeo-23-123-2005
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发表时间：
2002
影响因子：
1.9
通讯作者：
M. Fujimoto
中科院分区：
文献类型：
--
作者：
N. Østgaard;J. Moen;S. Mende;H. Frey;T. Immel;P. Gallop;K. Oksavik;M. Fujimoto
行星际磁场和地球磁场的昼侧合并将太阳风电场耦合到地球磁层，增加磁层对流，并导致太阳风能量有效地传输到磁层。随后，磁尾中的叶磁场重联将能量输送到闭合磁场区域。结合全球成像和地基雷达测量，我们估计在磁尾重联率在2000年11月至12月的EISCAT活动的两天。来自IMAGE FUV系统的全球图像指导我们识别由特罗姆瑟（VHF）和斯瓦尔巴（ESR）的两个EISCAT雷达观测到的开闭场线边界的电离层特征。开-闭场线边界的连续雷达和光学监测用于确定开-闭边界的位置、取向和速度以及垂直于该边界的离子流速度。发现磁尾重联电场是一个突发过程，周期在0 mV/m和1 mV/m之间振荡，周期为10 - 15 min。这些超低频振荡主要是由于开-闭边界的运动引起的。在地磁尾的重联点向地的原位测量表明，在黄昏电场中也有类似的振荡。我们还发现磁尾重连增加的爆发并不一定有任何相关的极光特征。最后，我们发现探测率与太阳风电场的相关性很差。这表明磁尾重联不是直接驱动的，而是一个内部磁层过程。太阳风电磁场和磁尾重联之间的耦合效率的估计似乎只是作为长时间间隔的平均值而相关。1 mHz的振荡模式对应于具有额外的较低频率（0.5和0.8 mHz）的内腔模式，其可能被太阳风压变化调制。
Dayside merging between the interplanetary and terrestrial magnetic fields couples the solar wind electric field to the Earth's magnetosphere, increases the magnetospheric convection and results in efficient transport of solar wind en- ergy into the magnetosphere. Subsequent reconnection of the lobe magnetic field in the magnetotail transports energy into the closed magnetic field region. Combining global imag- ing and ground-based radar measurements, we estimate the reconnection rate in the magnetotail during two days of an EISCAT campaign in November-December 2000. Global images from the IMAGE FUV system guide us to identify ionospheric signatures of the open-closed field line bound- ary observed by the two EISCAT radars in Tromso (VHF) and on Svalbard (ESR). Continuous radar and optical mon- itoring of the open-closed field line boundary is used to de- termine the location, orientation and velocity of the open- closed boundary and the ion flow velocity perpendicular to this boundary. The magnetotail reconnection electric field is found to be a bursty process that oscillates between 0 mV/m and 1 mV/m with 10-15 min periods. These ULF oscilla- tions are mainly due to the motion of the open-closed bound- ary. In situ measurements earthward of the reconnection site in the magnetotail by Geotail show similar oscillations in the duskward electric field. We also find that bursts of increased magnetotail reconnection do not necessarily have any asso- ciated auroral signatures. Finally, we find that the reconnec- tion rate correlates poorly with the solar wind electric field. This indicates that the magnetotail reconnection is not di- rectly driven, but is an internal magnetospheric process. Es- timates of a coupling efficiency between the solar wind elec- tric field and magnetotail reconnection only seem to be rel- evant as averages over long time intervals. The oscillation mode at 1 mHz corresponds to the internal cavity mode with additional lower frequencies, 0.5 and 0.8 mHz, that might be modulated by solar wind pressure variations.