Vector magnetic fields of moving magnetic features and flux removal from a sunspot

Moving magnetic features (MMFs) are small photospheric magnetic elements moving outward in the zone ( moat region) surrounding mature sunspots. Vector magnetic fields and horizontal motion of the classical MMFs ( called isolated MMFs hereafter) are investigated using coordinated ASP and MDI observations. Their magnetic and velocity properties are compared to nearby magnetic features, including moat fields surrounding the isolated MMFs and penumbral uncombed structure. The moat fields are defined as nonisolated MMFs because they also move outward from sunspots. The nonisolated MMFs have nearly horizontal magnetic fields of both polarities. We find that the isolated MMFs located on the lines extrapolated from the horizontal component of the uncombed structure have magnetic fields similar to the nonisolated MMFs. This suggests that the MMFs with nearly horizontal fields are intersections of horizontal fields extended from the penumbra with the photospheric surface. We find clear evidence that the isolated MMFs located on the lines extrapolated from the vertical component of the uncombed structure have vertical field lines with polarity same as the sunspot. This correspondence shows that such MMFs are detached from the spine ( vertical) component of the penumbra. We estimate that the magnetic flux carried by the vertical MMFs is about 1-3 times larger than the flux loss of the sunspot. We suggest that the isolated vertical MMFs alone can transport sufficient magnetic flux and are responsible for the disappearance and disintegration of the sunspot.