Magnetic correspondence between moving magnetic features and penumbral magnetic fields

We investigate vector magnetic fields of moving magnetic features (MMFs) around a mature sunspot with the Advanced Stokes Polarimeter and SOHO/MDI. In addition to the classical isolated MMFs identified by visually inspecting the time sequence of MDI magnetograms, we focus on any diffuse moving magnetic features that are not recognized as classical MMFs. This feature is called non-isolated MMFs. The non-isolated MMFs occupy most of the moat region surrounding the sunspot, and have nearly horizontal magnetic fields with both polarities. We find that the isolated MMFs located on the lines extrapolated from the horizontal component of the penumbral uncombed structure have magnetic fields similar to the non-isolated MMFs. This suggests that such MMFs are part of horizontal fields extended from the penumbra. The isolated MMFs located on the lines extrapolated from the vertical component of the uncombed structure have vertical fields with polarity same as the sunspot. Our observation shows that such MMFs are detached from the vertical component of the penumbra. Their flux transport rate is estimated to be 1-3 times larger than a flux loss rate of the sunspot. The isolated vertical MMFs alone can be responsible for decaying the sunspot.