Study on Precursor Activity of the X1.6 Flare in the Great AR 12192 with SDO, IRIS, and Hinode

<jats:title>Abstract</jats:title> <jats:p>The physical properties and their contribution to the onset of a solar flare are still uncleare even though chromospheric brightening is considered a precursor phenomenon of a flare. Many studies suggested that photospheric magnetic field changes cause destabilization of large-scale coronal structure. We aim to understand how a small photospheric change contributes to a flare and to reveal how the intermediary chromosphere behaves in the precursor phase. We analyzed the precursor brightening of the X1.6 flare on 2014 October 22 in the AR 12192 using the <jats:italic>Interface Region Imaging Spectrograph</jats:italic> (<jats:italic>IRIS</jats:italic>) and <jats:italic>Hinode</jats:italic>/EUV Imaging Spectrometer (EIS) data. We investigated a localized jet with the strong precursor brightening, and compared the intensity, Doppler velocity, and line width in C <jats:sc>ii</jats:sc>, Mg <jats:sc>ii</jats:sc> k, and Si <jats:sc>iv</jats:sc> lines by <jats:italic>IRIS</jats:italic> and He <jats:sc>ii</jats:sc>, Fe <jats:sc>xii</jats:sc>, and Fe <jats:sc>xv</jats:sc> lines by <jats:italic>Hinode</jats:italic>/EIS. We also analyzed the photospheric magnetic field and chromospheric/coronal structures using the <jats:italic>Solar Dynamics Observatory</jats:italic> (<jats:italic>SDO</jats:italic>)/Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly. We found a significant blueshift (∼100 km s<jats:sup>−1</jats:sup>), which is related to the strong precursor brightening over a characteristic magnetic field structure, and the blueshift was observed at all of the temperatures. This might indicate that the flow is accelerated by Lorentz force. Moreover, the large-scale coronal loop that connects the foot points of the flare ribbons was destabilized just after the precursor brightening with the blueshift. It suggests that magnetic reconnection locally occurred in the lower chromosphere and it triggered magnetic reconnection of the X1.6 flare in the corona.</jats:p>