Pi2 Pulsations During Extremely Quiet Geomagnetic Condition: Van Allen Probe Observations
Pi2 Pulsations During Extremely Quiet Geomagnetic Condition: Van Allen Probe Observations
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极其安静的地磁条件下的 Pi2 脉动：范艾伦探测器观测
DOI：
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发表时间：
2017
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影响因子：
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通讯作者：
E. Ghamry
中科院分区：
文献类型：
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作者：
E. Ghamry
据报道，在磁层和太阳风极其平静的时期会出现一种超低频波Pi 2。据作者所知，在极其安静的条件下，没有使用卫星观测对Pi 2进行统计研究。此外，近地点附近的空间磁通门磁力计中的Pi 2脉动以前未能引起科学家的注意。本文对货车艾伦探测卫星（VAP-A和VAP-B）探测到的Pi 2脉动进行了统计研究。在2012年10月至2014年12月期间，当Kp = 0时，使用VAP识别出96个Pi 2事件，同时使用Kakioka（KAK，L = 1.23）作为参考地面站。在KAK站，75个事件的VAP-Bz和H分量之间有很高的一致性。结果发现，77%的事件具有5至12 mHz之间的功率谱，这不同于6.7至25 mHz的常规Pi 2频带范围。此外，还表明有可能从近地点附近的空间磁通门磁强计观测到Pi 2脉动。本文发现了22个L < 4的Pi_2脉动，并给出了4个不同L壳层上Pi_2振荡的例子。
A ultra low frequency (ULF) wave, Pi2, has been reported to occur during periods of extremely quiet magnetospheric and solar wind conditions. And no statistical study on the Pi2 has been performed during extremely quiet conditions, using satellite observations to the author’s knowledge. Also Pi2 pulsations in the space fluxgate magnetometers near perigee failed to attract scientist’s attention previously. In this paper, Pi2 pulsations detected by the Van Allen probe satellites (VAP-A & VAP-B) were investigated statistically. During the period from October 2012 to December 2014, ninety six Pi2 events were identified using VAP when Kp = 0 while using Kakioka (KAK, L = 1.23) as a reference ground station. Seventy five events had high coherence between VAP-Bz and H components at KAK station. As a result, it was found that 77 % of the events had power spectra between 5 and 12 mHz, which differs from the regular Pi2 band range of from 6.7 to 25 mHz. In addition, it was shown that it is possible to observe Pi2 pulsations from space fluxgate magnetometers near perigee. Twenty two clean Pi2 pulsations were found where L < 4 and four examples of Pi2 oscillations at different L shells are presented in this paper.