Substorms and Their Solar Wind Causes |
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Authors: | Rumi Nakamura |
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Institution: | (1) Space Research Institute, Austrian Academy of Sciences, A-8042 Graz, Austria |
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Abstract: | Consequences of the solar wind input observed as large scale magnetotail dynamics during substorms are reviewed, highlighting
results from statistical studies as well as global magnetosphere/ionosphere observations. Among the different solar wind input
parameters, the most essential one to initiate reconnection relatively close to the Earth is a southward IMF or a solar wind
dawn-to-dusk electric field. Larger substorms are associated with such reconnection events closer to the Earth and the magnetotail
can accumulate larger amounts of energy before its onset. Yet, how and to what extent the magnetotail configuration before
substorm onset differs for different solar wind driver is still to be understood. A strong solar wind dawn-to-dusk electric
field is, however, only a necessary condition for a strong substorm, but not a sufficient one. That is, there are intervals
when the solar wind input is processed in the magnetotail without the usual substorm cycle, suggesting different modes of
flux transport. Furthermore, recent global observations suggest that the magnetotail response during the substorm expansion
phase can be also controlled by plasma sheet density, which is coupled to the solar wind on larger time-scales than the substorm
cycle. To explain the substorm dynamics it is therefore important to understand the different modes of energy, momentum, and
mass transport within the magnetosphere as a consequence of different types of solar wind-magnetosphere interaction with different
time-scales that control the overall magnetotail configuration, in addition to the internal current sheet instabilities leading
to large scale tail current sheet dissipation. |
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Keywords: | solar wind substorm magnetotail |
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