Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Origin of Strong-Field Polarity Inversion Lines   Several studies have correlated observations of impulsive solar activity --
flares and coronal mass ejections (CMEs) -- with the amount of magnetic flux
near strong-field polarity inversion lines (PILs) in active regions'
photospheric magnetic fields, as measured in line-of-sight (LOS) magnetograms.
Practically, this empirical correlation holds promise as a space weather
forecasting tool. Scientifically, however, the mechanisms that generate strong
gradients in photospheric magnetic fields remain unknown. Hypotheses include:
the (1) emergence of highly twisted or kinked flux ropes, which possess strong,
opposite-polarity fields in close proximity; (2) emergence of new flux in close
proximity to old flux; and (3) flux cancellation driven by photospheric flows
acting fields that have already emerged. If such concentrations of flux near
strong gradients are formed by emergence, then increases in unsigned flux near
strong gradients should be correlated with increases in total unsigned magnetic
flux -- a signature of emergence. Here, we analyze time series of MDI
line-of-sight (LOS) magnetograms from several dozen active regions, and
conclude that increases in unsigned flux near strong gradients tend to occur
during emergence, though strong gradients can arise without flux emergence. We
acknowledge support from NSF-ATM 04-51438.

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The categories of this paper are: cs
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The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: cond-mat
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: stat
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The categories of this paper are: supr-con
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The categories of this paper are: acc-phys
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The categories of this paper are: eess