The multiscale magnetic pattern and the roots of solar activity

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The multiscale magnetic pattern and the roots of
solar activity

• F. Berrilli, S. Scardigli, D. Del Moro
• Department of Physics, University of Rome Tor
  Vergata, Italy (berrilli_at_roma2.inf.it)

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The nature of the multiscale convective pattern
observed on the solar surface remains a
long-standing puzzle in solar physics.
Size of a realistic MHD simulation domain
The convective dynamo is the source of solar
magnetism that modulates the activity of the Sun,
creates active regions and drives Space
Weather. The analysis of solar magnetic pattern
provides a way to investigate all the
organization scales of convection, from
granulation to the global circulation.
HR MDI Mag
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If we observe the Sun we see that the magnetic
fields do not fill photosphere uniformly but
instead are clustered in a network with large
voids (relatively empty regions) between them.
The inspection of photospheric magnetograms that
were taken at the limits of the available
resolution reveals regions where magnetic fields
are weak and very inclined (commonly named
voids). A division of such voids in classical
scales (i.e., granulation, meso-granulation,
super-granulation) is probably of historical and
not physical origin (Nordlund et al., 2009).
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We study the void size distribution (VSD) to
determine whether it reveals distinct flow scales
or it is smoothly distributed. The analysis was
performed on a series of SOHO/MDI LOS
magnetograms acquired during the solar activity
minimum between cycles 23 and 24 and the
Hinode/SOT/SP LOS magnetogram observed at disk
center on 10 March 2007. We have analyzed a
dataset of 511 high-resolution quiet Sun MDI
magnetograms selected to cover a period of 18
months from 1/1/2008. The void-detection
algorithm singled out 252 488 and 1951 voids in
MDI and HINODE magnetograms, respectively.
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Conclusions VSD shows a quasi-exponential decay
in the observed ranges. The lack of features in
the 260 Mm range supports the multiscale
hypothesis of convective motion flows at the
solar surface (e.g., Nordlund et al. 2009
Rieutord et al. 2010, Yelles Chaouche et al.
2011 Berrilli et al. 2013). Berrilli F.,
Scardigli S., Giordano S., Multiscale Magnetic
Underdense Regions on the Solar Surface Granular
and Mesogranular Scales, Solar Physics, 282,
2013 Berrilli F., Scardigli S., Del Moro D.,
Magnetic pattern at super-granulation scale the
void size distribution, AA 568, 2014