A Solar Eruption with Relatively Strong Geo-effectiveness Originating from Active Region Peripheral Diffusive Polarities

We report the observations of a moderate but relatively intense geo-effective solar eruption on 2015 November 4 from the peripheral diffusive polarities of active region 12443. We use space-borne Solar Dynamics Observatory and ACE observations. EUV images identified helical pattern along a filament channel and we regard this channel as flux-rope structure. Flow velocity derived from tracked magnetograms infers converging motion along the polarity inversion line beneath the filament channel. An associated magnetic cancellation process was detected in the converging region. Further, the pre-eruptive EUV brightening was observed in the converging region, the most intense part of which appeared in the magnetic cancellation region. These observations imply that the converging and cancelling flux probably contributed to the formation of the helical magnetic fields associated with the flux rope. A filament-height estimation method suggests that the middle part of the filament probably lies at a low altitude and was consistent with the initial place of the eruption. A thick current channel associated with the flux rope is also determined. For a expanding thick current channel, the critical height of the decay index for torus instability lies in the range of 37 - 47 Mm. Southward magnetic fields in the sheath and the ejecta induced a geomagnetic storm with a Dst global minimum of ~-90 nT.
Comment: Accepted for publication in ApJ