Solar wind and magnetospheric conditions leading to the abrupt loss of outer radiation belt electrons
Solar wind and magnetospheric conditions leading to the abrupt loss of outer radiation belt electrons
复制标题
太阳风和磁层条件导致外辐射带电子突然损失
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
H. Singer
中科院分区：
文献类型：
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作者：
T. Onsager;J. Green;G. Reeves;H. Singer
[1]被捕获的辐射带的电子人口是通过多个源之间的竞争和磁层内发生的损失过程，并由太阳风驱动。在这项研究中，我们集中在太阳风和磁层条件，导致损失的电子通过突然高能电子通量辍学。我们把重点放在只有中等水平的地磁活动的时候，因为在这些条件下的磁层响应预计远不如在大磁暴期间复杂。我们发现，在某些情况下，辐射带电子对向南IMF的开始和太阳风动压的增加非常敏感。向南IMF的发病被认为是足以导致通量辍学，而太阳风压力的增加是不必要的，但很可能会增加损失时，他们发生在与向南IMF，往往是这样。目前尚不清楚在没有向南IMF的情况下，太阳风压力的增加是否足以导致通量下降。辐射带的通量可以减少一个数量级以上，只有轻微的地磁活动的开始。造成通量损失的太阳风强迫水平（由太阳风参数估计）和地磁活动水平（由AE、Dst和地球同步轨道上的局部磁场倾角估计）介于较低水平的活动和导致通量损失和加速的大磁暴之间。这里检查的辍学事件发生后，一天或多天的安静的地磁条件下，我们建议预处理的磁层是高度敏感的新活动的开始。虽然不知道磁层内的哪些特定条件导致相对论性电子的这种极端敏感性，但这里确定的时间段是电子损失过程似乎与加速过程相对隔离的时间段。
[1] The trapped radiation belt electron population is maintained through a competition between multiple source and loss processes occurring within the magnetosphere and driven by the solar wind. In this research we have concentrated on the solar wind and the magnetospheric conditions that lead to the loss of electrons through abrupt energetic electron flux dropouts. We have focused on times when there is only a moderate level of geomagnetic activity, since the magnetospheric response during these conditions is expected to be far less complex than during large geomagnetic storms. We have found that under certain circumstances the radiation belt electrons are remarkably sensitive to the onset of southward IMF and to solar wind dynamic pressure increases. The onset of southward IMF is found to be sufficient to cause the flux dropouts, while increases in solar wind pressure are not necessary but are likely to enhance the loss when they occur in conjunction with southward IMF, as is often the case. It is not clear if an increase in solar wind pressure in the absence of southward IMF is sufficient to cause a flux dropout. The radiation belt fluxes can decrease by more than an order of magnitude with the onset of only minor geomagnetic activity. The level of solar wind forcing (as estimated by the epsilon parameter) and of geomagnetic activity (as estimated by AE, Dst, and the local magnetic field inclination at geosynchronous orbit) responsible for the flux loss is intermediate between lower levels of activity that create localized, adiabatic variations in the flux and large geomagnetic storms that result in both loss and acceleration. The dropout events examined here occurred after one or more days of quiet geomagnetic conditions, which we suggest preconditioned the magnetosphere to be highly sensitive to the onset of new activity. Although it is not known which specific conditions within the magnetosphere lead to this extreme sensitivity of the relativistic electrons, the time periods identified here are ones where the electron loss processes appear to operate in relative isolation of the acceleration processes.