Title: Observations and Modelling of the Pre-Flare Period of the 29 March 2014 X1 Flare,
Abstract: On the 29 March 2014 NOAA active region (AR) 12017 produced an X1 flare which
was simultaneously observed by an unprecedented number of observatories. We
have investigated the pre-flare period of this flare from 14:00 UT until 19:00
UT using joint observations made by the Interface Region Imaging Spectrometer
(IRIS) and the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Spectral
lines providing coverage of the solar atmosphere from chromosphere to the
corona were analysed to investigate pre-flare activity within the AR. The
results of the investigation have revealed evidence of strongly blue-shifted
plasma flows, with velocities up to 200 km/s, being observed 40 minutes prior
to flaring. These flows are located along the filament present in the active
region and are both spatially discrete and transient. In order to constrain the
possible explanations for this activity, we undertake non-potential magnetic
field modelling of the active region. This modelling indicates the existence of
a weakly twisted flux rope along the polarity inversion line in the region
where a filament and the strong pre-flare flows are observed. We then discuss
how these observations relate to the current models of flare triggering. We
conclude that the most likely drivers of the observed activity are internal
reconnection in the flux rope, early onset of the flare reconnection, or tether
cutting reconnection along the filament.