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On the 29 March 2014 NOAA active region (AR) 12017 produced an X1 flare whichwas simultaneously observed by an unprecedented number of observatories. Wehave investigated the pre-flare period of this flare from 14:00 UT until 19:00UT using joint observations made by the Interface Region Imaging Spectrometer(IRIS) and the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Spectrallines providing coverage of the solar atmosphere from chromosphere to thecorona were analysed to investigate pre-flare activity within the AR. Theresults of the investigation have revealed evidence of strongly blue-shiftedplasma flows, with velocities up to 200 km/s, being observed 40 minutes priorto flaring. These flows are located along the filament present in the activeregion and are both spatially discrete and transient. In order to constrain thepossible explanations for this activity, we undertake non-potential magneticfield modelling of the active region. This modelling indicates the existence ofa weakly twisted flux rope along the polarity inversion line in the regionwhere a filament and the strong pre-flare flows are observed. We then discusshow these observations relate to the current models of flare triggering. Weconclude that the most likely drivers of the observed activity are internalreconnection in the flux rope, early onset of the flare reconnection, or tethercutting reconnection along the filament.

Observations and Modelling of the Pre-Flare Period of the 29 March 2014 X1 Flare