On the Relation between Surge Activities and a Photospheric Horizontal Velocity Field

Abstract

A photospheric horizontal velocity field was observed in an active region, NOAA 8375, which showed high Hα surge activities on 1998 November 6. From analyses of Hα images, the photospheric horizontal velocity field, and the magnetic field in and around the active region, we found the following: (1) Meso-granular or supergranular photospheric horizontal motions were found to be suppressed in the active region where the magnetic filed strength was high. No systematic large-scale flows were found carrying the moving satellite spots with them. (2) Roots of Hα surges were situated near a magnetic neutral line, where photospheric horizontal flow converged. Anti-polar magnetic fields on both sides of the neutral line were pushed together by the photospheric horizontal velocity field of meso-granular scales. Magnetic cancellation or magnetic reconnection in the chromospheric and/or photospheric layers at a magnetic neutral line accelerated by photospheric horizontal flows may be the origin of the observed Hα surge activities.