Statistical Analysis of Asymmetric Sunspot Decay Observed by Hinode

Abstract

We statistically studied the transport of magnetic flux in and around sunspots using a magnetic-element tracking technique to investigate whether sunspot-decay processes are isotropic. Using this method, we detected moving magnetic features (MMFs). The observed radius of an MMFs region was approximately 1.7 times the sunspot radius; furthermore, the average apparent velocity of MMFs was statistically estimated to be approximately $350~\mbox{m}\,\mbox{s}^{-1}$ . We determined that the leading sunspots transport approximately 5% more magnetic flux to the Equator side than to the Pole side of the sunspots. In addition, the leading sunspots transport approximately 3% more magnetic flux to the back (East) than to the front (West) of the sunspots. On the other hand, the following sunspots do not show the magnetic-flux transport asymmetry. The statistics might not be sufficient for the analysis of the following sunspots. These asymmetries of magnetic flux transport might contribute to the cross-equatorial transport of net magnetic flux, which is an important physical quantity of polar magnetic-field reversal.