Spectropolarimetric Measurements Of The Inverse Evershed Flow

We use high spatial resolution observations with spectropolarimeters at the Dunn Solar Telescope in multiple spectral lines originating in the chromosphere to study inverse Evershed flow channels that connect the outer penumbra and the moat region around sunspots at various heliocentric positions. The measurements were combined with extrapolated magnetic field lines to determine the three-dimensional topology of the flow channels. The magnetic field lines guiding the flows reach on average a height of 2-5 Mm over a length of 10-20 Mm, with cold inner (hot outer) foot points located at 1.2 (1.9) sunspot radii. The average difference in field strength between the inner and outer foot point is about +400 G, while the temperature difference is about -100 K. This configuration can drive and sustain a siphon flow from the moat boundary towards the penumbra over the lifetime of the flow channels of about one hour. This study clearly demonstrates the inverse Evershed flow to be a siphon flow along arched chromospheric loops.