Fine-Scale Structures of the Evershed Effect Observed by the Solar Optical Telescope aboard Hinode

Abstract

The small-scale structure of the Evershed effect is being studied using data obtained by the Spectropolarimeter and the Broadband Filter Imager of the Solar Optical Telescope aboard Hinode. We find that the Evershed flow starts at the leading edge of inwardly migrating bright penumbral grains, and turns to nearly a horizontal flow preferentially in the dark lanes of the penumbra. A number of small elongated regions that have an upward motion of $\sim$1 km s$^{-1}$ are found in the deep photosphere distributed over the penumbra. They are cospatial with bright grains and have relatively horizontal magnetic fields. A number of patches having a strong downward motion associated with the opposite magnetic polarity from the sunspot are also found in the mid and outer penumbra. They could be identified as foot points of the Evershed flow channels, though the identification of individual pairs is not straightforward. Our results provide strong support for some recent findings from ground-based high-resolution observations, and are in general agreement with the well-known picture of the uncombed structure of the penumbra, in which the penumbrae consist of rising flux tubes carrying nearly horizontal Evershed flows embedded in more vertical background magnetic fields.