Abstract
A superposed epoch analysis is conducted for five geomagnetic storms in the years 2005 and 2006 with the aim to understand energetic particle flux variations as a function of L-shell, energy and time from the Dst minimum. Data measured by the low-altitude DEMETER spacecraft were used for this purpose. The storms were identified by a Dst index below −100 nT, as well as their being isolated events in a seven-day time window. It is shown that they can be categorized into two types. The first type shows significant variations in the energetic particle fluxes around the Dst minimum and increased fluxes at high energies (>1.5 MeV), while the second type only shows increased fluxes around the Dst minimum without the increased fluxes at high energies. The first type of storm is related to more drastic but shorter-lasting changes in the solar wind parameters than the second type. One storm does not fit either category, exhibiting features from both storm types. Additionally, we investigate whether the impenetrable barrier for ultra-relativistic electrons also holds in extreme geomagnetic conditions. For the highest analyzed energies, the obtained barrier L-shells do not go below 2.6, consistent with previous findings.
Highlights
Disturbances in the Earth’s magnetosphere are often caused by geomagnetic storms (e.g., [1]). These can have a serious impact on satellites as well as on power grids, communication and navigation on Earth. They are caused by solar wind-magnetosphere interaction through the magnetic reconnection mechanism [2,3,4]
The storms are characterized by a depression in the horizontal component of the geomagnetic field
The strength of the storms is often expressed in the disturbance storm time (Dst), index [11,12,13]
Summary
Disturbances in the Earth’s magnetosphere are often caused by geomagnetic storms (e.g., [1]) These can have a serious impact on satellites as well as on power grids, communication and navigation on Earth. They are caused by solar wind-magnetosphere interaction through the magnetic reconnection mechanism [2,3,4]. This interaction causes enhanced energetic particle fluxes in the radiation belts [5,6,7,8] and an increased ring current encircling Earth [9,10]. The strength of the storms is often expressed in the disturbance storm time (Dst), index [11,12,13]
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