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 H$\alpha $ surge activities on 1998 November 6. From analyses of H$\alpha $ 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 H$\alpha $ 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 H$\alpha $ surge activities.