Authors: Ian Berry (Institute for Astronomy, University of Hawai'i'), Xudong Sun (Institute for Astronomy, University of Hawai'i'), Sarah Jaeggli (National Solar Observatory), Wei Liu (Lockheed Martin Solar and Astrophysics Laboratory)

Solar active region (AR) photospheric magnetic fields undergo rapid evolution during major eruptions. Specifically, the horizontal magnetic field component near the main polarity inversion line of the AR sees permanent increases of order hundreds of Gauss over several minutes. The resulting Lorentz force acts on the dense, lower atmosphere, capable of drawing material upwards from the photosphere. This “gentle photospheric upwelling” is expected to occur in the AR core situated between flare ribbons with mean velocity estimates on the order of tens of meters per second. To investigate this phenomenon, we use near-ultraviolet (NUV) observations of photospheric absorption lines (in the Mg II h&k line wings) taken by the Interface Region Imaging Spectrometer (IRIS), as well as vector magnetic field observations taken by the Helio Magnetic Imager (HMI) to search for such Doppler signal. X1.0 and X1.1 class solar flares observed by IRIS occurring respectively on 2014 March 29 and 2023 February 11 are analyzed. We extract the Doppler velocities for a number of lines at varying formation heights. Our initial results show that Doppler velocities of the AR core during the flare are statistically different from the pre-flare state with both more extreme blueshifts and redshifts present. There is no obvious trend as a function of height. We discuss the implication of our findings on the “gentle photospheric upwelling” hypothesis.