Asymmetric distribution of weak photospheric magnetic field values. (arXiv:1904.10866v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Getachew_T/0/1/0/all/0/1">Tibebu Getachew</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Virtanen_I/0/1/0/all/0/1">Ilpo Virtanen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mursula_K/0/1/0/all/0/1">Kalevi Mursula</a>
We use the synoptic maps of the photospheric magnetic field observed at
Wilcox Solar Observatory, Mount Wilson Observatory, Kitt Peak, SOHO/MDI,
SOLIS/VSM, and SDO/HMI to study the distribution of weak photospheric magnetic
field values in 1974-2018. We fit the histogram distribution of weak field
values for each synoptic map of the six data-sets separately with a
parametrized Gaussian function in order to calculate the possible shift (to be
called here the weak-field asymmetry) of the maximum of the Gaussian
distribution from zero. We estimate the statistical significance of the
weak-field asymmetry for each rotation. We also calculate several versions of
lower-resolution synoptic maps from the high-resolution maps and calculate
their rotational weak-field asymmetries. We find that the weak-field
asymmetries increase with decreasing map resolution. A very large fraction of
weak-field asymmetries are statistically significant, with the fraction of
significant weak-field asymmetries increasing with decreasing resolution.
Significant weak-field asymmetries of high- and low-resolution maps mainly
occur at the same times and have the same sign. Weak-field asymmetries for the
different data-sets and resolutions vary quite similarly in time, and their
mutual correlations are very high, especially for low-resolution maps. These
results give strong evidence for weak-field asymmetries reflecting a real
feature of weak field values, which is best seen in medium- and low-resolution
synoptic maps and is most likely related to the supergranulation scale of the
photospheric field.
We use the synoptic maps of the photospheric magnetic field observed at
Wilcox Solar Observatory, Mount Wilson Observatory, Kitt Peak, SOHO/MDI,
SOLIS/VSM, and SDO/HMI to study the distribution of weak photospheric magnetic
field values in 1974-2018. We fit the histogram distribution of weak field
values for each synoptic map of the six data-sets separately with a
parametrized Gaussian function in order to calculate the possible shift (to be
called here the weak-field asymmetry) of the maximum of the Gaussian
distribution from zero. We estimate the statistical significance of the
weak-field asymmetry for each rotation. We also calculate several versions of
lower-resolution synoptic maps from the high-resolution maps and calculate
their rotational weak-field asymmetries. We find that the weak-field
asymmetries increase with decreasing map resolution. A very large fraction of
weak-field asymmetries are statistically significant, with the fraction of
significant weak-field asymmetries increasing with decreasing resolution.
Significant weak-field asymmetries of high- and low-resolution maps mainly
occur at the same times and have the same sign. Weak-field asymmetries for the
different data-sets and resolutions vary quite similarly in time, and their
mutual correlations are very high, especially for low-resolution maps. These
results give strong evidence for weak-field asymmetries reflecting a real
feature of weak field values, which is best seen in medium- and low-resolution
synoptic maps and is most likely related to the supergranulation scale of the
photospheric field.
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