On the solar wind control of Pc5 ULF pulsation power at mid‐latitudes: Implications for MeV electron acceleration in the outer radiation belt
On the solar wind control of Pc5 ULF pulsation power at mid‐latitudes: Implications for MeV electron acceleration in the outer radiation belt
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DOI：
10.1029/2001ja000002
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发表时间：
2001-12
影响因子：
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通讯作者：
R. A. Mathie;I. Mann
中科院分区：
文献类型：
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作者：
R. A. Mathie;I. Mann
本文根据国际极光地磁事件监测仪(IMAGE)磁力仪阵列的6个测点(L壳距3.75-6.79)的观测资料，统计研究了1995年、1996年和1997年太阳风速与日超低频脉动功率的关系，这段时间对应于太阳第22周的下降阶段。在所研究的整个L壳层范围内，我们发现太阳风速与日侧磁层脉动功率之间存在很强的正相关关系。此外，我们根据DST的变化确定了一些地磁风暴的开始日，并证明在这些天里，只有在中等太阳风速条件下才能驱动大幅度的超低频脉动活动。去除起始日总体改善了脉动功率与太阳风速的相关性，并演示了如何通过考虑DST来确定基于脉动功率的改进的太阳风速代理。我们还证明了1-10 MHzPc5波功率随L壳层的减小而指数衰减，衰减率随太阳风速的增大而增大，从而表明在较高的L壳层，在L=3.75-6.79时，脉动功率对太阳风速的依赖性更强。此外，所研究的L壳层范围与在外辐射带观测到的MeV电子通量在风暴时间内增强的范围是一致的，我们讨论了PCS超低频波功率与太阳风速和L壳层的依赖关系对于风暴时间超低频脉动导致能量电子加速的机制的意义。
On the basis of observations made at six sites (L shell range 3.75–6.79) belonging to the International Monitor for Auroral Geomagnetic Events (IMAGE) magnetometer array, we provide a statistical study of the relationship of solar wind speed to daily ULF pulsation power for 1995, 1996, and 1997, an interval corresponding to the declining phase of solar cycle 22. We find a very strong positive correlation between solar wind speed and dayside magnetospheric pulsation power across the entire L shell range studied. In addition, we identify a number of geomagnetic storm onset days on the basis of Dst variations and demonstrate that on these days large-amplitude ULF pulsation activity can be driven during only moderate solar wind speed conditions. Removing the onset day population improves the correlation of pulsation power to solar wind speed and demonstrates how an improved solar wind speed proxy based on pulsation power can be determined by considering Dst. We also demonstrate an exponential decay of 1–10 mHz Pc5 wave power with decreasing L shell, the decay rate increasing with solar wind speed, thus indicating a stronger dependence of pulsation power on solar wind speed at higher L shells in the range L=3.75–6.79. Further, the L shell range studied is consistent with that over which storm-time enhancements of MeV electron fluxes have been observed in the outer radiation belt, and we discuss the implications of the dependence of PcS ULF wave power on both solar wind speed and L shell for mechanisms which implicate large-amplitude ULF pulsations in the acceleration of storm-time MeV energy electrons.