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Ann. Geophys., 20, 741-755, 2002
www.ann-geophys.net/20/741/2002/
© European Geosciences Union 2002
Evolutions of various solar indices around sunspot maximum and sunspot minimum years
R. P. Kane
Instituto Nacional de Pesquisas Espacias, C. P. 515 São José dos Campos, 12201-970, SP, Brazil
Correspondence to: R. P. Kane (kane@laser.inpe.br)
Abstract. The smoothed monthly
sunspot numbers showed that in many solar cycles, (a) during years around
sunspot maxima, there was only one prominent maximum, but in some cycles there
was a broad plateau. If the beginning and end of these are termed as first and
second maxima (separated by several months), the first maximum was generally
the higher one, and the valley in between was very shallow. Solar indices at or
near the photosphere generally showed similar structures with maxima matching
with sunspot maxima within a month or two. Indices originating in the
chromosphere and above showed two peaks in roughly the same months as sunspots
(with some exceptions, notably the Coronal green line, and the Total Solar
Irradiance). Yet often, the second maximum was larger than the first maximum,
and the valley between the two maxima was deeper, as compared to sunspot maxima,
and (b) during years around sunspot minima, the smoothed sunspot minimum could
be sharp and distinct, lasting for a month or two, or could spread over several
months. Among the indices originating at or near the photosphere, the Ca K line
intensity showed good matching with sunspots, but the Ca Plage area, the
Sunspot Group Area, and the solar magnetic fields seemed to show minima earlier
than the sunspots, indicating that these activities died out first. These also
showed recoveries from the minima later than sunspots. Most of the other
indices originating in the chromosphere and corona attained minima coincident
with sunspot minima, but in some cases, minima earlier than sunspots were seen,
while in some other cases minima occurred after the sunspot minima. Thus, the
energy dissipation in the upper part of the solar atmosphere sometimes lagged
or led the evolution of sunspots near sunspot minimum. In a few cases, after
the minimum, the indices recovered faster than the sunspots. In general, the
chromospheric indices seemed to evolve similar to sunspots, but the evolution
of coronal indices was not always similar to sunspots, and may differ
considerably between themselves.
Key words. Solar physics,
astrophysics and astronomy (Corona and transition region; Magnetic fields;
Photosphere and chromosphere)
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