Three-Dimensional Magnetic and Velocity Structures of Active Region 12673

We study the Solar Active Region (AR) 12673 in September 2017, which is the most flare productive AR in the solar cycle 24.  Observations from Goode Solar Telescope (GST) show the strong photospheric magnetic fields (nearly 6000 G) in polarity  inversion line (PIL) and apparent photospheric twist on September 6,  the day of X9.3 flare. Corresponding to the strong twist,   upflows are observed to last one day  at the center part of that section of PIL;  down flows are observed in two ends.  Transverse velocity fields are derived from flow tracking.   Both Non-Linear Force-Free Field (NLFFF) and Non-Force-Free Field (NFFF) extrapolations are carried out and compared to trace 3-D magnetic fields in corona. Combining with EOVSA, coronal magnetic fields between 1000 and 2000 gauss are found above the flaring PIL at the height range between 8 and 4Mm, outlining the structure of a fluxrope with sheared arcade.  The above magnetic and velocity fields, as well as thermal structure of corona, provide initial condition for further data-driven MHD simulation.