Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: What causes geomagnetic activity during sunspot minimum   The average geomagnetic activity during sunspot minimum has been continuously
decreasing in the last four cycles. The geomagnetic activity is caused by both
interplanetary disturbances - coronal mass ejections and high speed solar wind
streams, and the background solar wind over which these disturbances ride. We
show that the geomagnetic activity in cycle minimum does not depend on the
number and parameters of coronal mass ejections or high speed solar wind
streams, but on the background solar wind. The background solar wind has two
components: slower and faster. The source of the slower component is the
heliospheric current sheet, and of the faster one the polar coronal holes. It
is supposed that the geomagnetic activity in cycle minimum is determined by the
thickness of the heliospheric current sheet which is related to the portions of
time the Earth spends in slow and in fast solar wind. We demonstrate that it is
also determined by the parameters of these two components of the background
solar wind which vary from cycle to cycle.

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The categories of this paper are: gr-qc
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: mtrl-th