  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.
