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| Titel |
Probing latitudinal variations of the solar magnetic field in cycles 21–23 by Parker's Two-Layer Dynamo Model with meridional circulation |
| VerfasserIn |
E. Popova, V. Zharkova, S. Zharkov |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 31, no. 11 ; Nr. 31, no. 11 (2013-11-20), S.2023-2038 |
| Datensatznummer |
250086148
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| Publikation (Nr.) |
 copernicus.org/angeo-31-2023-2013.pdf |
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| Zusammenfassung |
Principle component analysis (PCA) of the solar background magnetic field
(SBMF) measured from Wilcox Solar Observatory (WSO) magnetograms revealed the
following principal components (PCs) in latitudes: two main symmetric
components, which are the same for all cycles 21–23, and three pairs of
asymmetric components, which are unique for each cycle. These SBMF variations
are assumed to be those of poloidal magnetic field travelling slightly
off-phase from pole to pole while crossing the equator. They are assumed to
be caused by a joint action of dipole and quadruple magnetic sources in the
Sun.
In the current paper, we make the first attempt to interpret these latitudinal
variations in the surface magnetic field with Parker's two-layer dynamo
model. The latitudinal distributions of such waves are simulated for cycles
21–23 by the modified Parker's dynamo model taking into account both
α and ω effects operating simultaneously in the two (upper and
lower) layers of the solar convective zone (SCZ) and having opposite
directions of meridional circulation. The simulations are carried out for
both dipole and quadruple magnetic sources with the dynamo parameters
specifically selected to provide the curves fitting closely the PCs derived
from SBMF variations in cycles 21–23. The simulations are optimised for
matching the positions of maximums in latitude, the number of equator
crossings and the phase difference between the two dynamo waves operating in
the two layers. The dominant pair of PCs present in each cycle is found to be
fully asymmetric with respect to the magnetic poles and produced by a
magnetic dipole. This pair is found to account for the two main dynamo waves
operating between the two magnetic poles. There are also three further pairs
of waves unique to each cycle and associated with multiple magnetic sources
in the Sun. For the odd cycle 21 the simulated poloidal field fits the
observed PCs, only if they are produced by magnetic sources with a quadruple
symmetry in both layers, while for the even cycle 22 the fit to the observed
PCs is achieved only in the case of quadruple magnetic sources in the upper
layer and dipole sources in the inner layer. For the other odd cycle 23 the
fit to observation is obtained for the quadruple magnetic sources in the
inner layer and the dipole sources in the upper layer. The magnitudes of
dynamo numbers D defining the conditions (depth and latitude) of a magnetic
flux formation and the numbers N of zeros (equator crossings by the waves)
are found to increase and the meridional circulation speed to decrease with a
cycle number increase (D = −700, N = 3 for cycle 21 and
D = −104, N = 9 for cycle 23). The phase delays between the
waves in each unique pairs are also found to increase with the cycle number
from ~9° in cycle 21 to ~13° in cycle 23. |
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