Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Periodicities in sunspot activity during solar cycle 23   The data of sunspot numbers, sunspot areas and solar flare index during cycle
23 are analyzed to investigate the intermediate-term periodicities. Power
spectral analysis has been performed separately for the data of the whole disk,
northern and southern hemispheres of the Sun. Several significant midrange
periodicities ($\sim$175, 133, 113, 104, 84, 63 days) are detected in sunspot
activity. Most of the periodicities in sunspot numbers generally agree with
those of sunspot areas during the solar cycle 23. The study reveals that the
periodic variations in the northern and southern hemispheres of the Sun show a
kind of asymmetrical behavior. Periodicities of $\sim$175 days and $\sim$133
days are highly significant in the sunspot data of northern hemisphere showing
consistency with the findings of Lean (1990) during solar cycles 12-21. On the
other hand, southern hemisphere shows a strong periodicity of about 85 days in
terms of sunspot activity. The analysis of solar flare index data of the same
time interval does not show any significant peak. The different periodic
behavior of sunspot and flare activity can be understood in the light of
hypothesis proposed by Ballester et al. (2002), which suggests that during
cycle 23, the periodic emergence of magnetic flux partly takes place away from
developed sunspot groups and hence may not necessarily increase the magnetic
complexity of sunspot groups that leads to the generation of flares.

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The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-th
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: hep-ph
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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: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys