The Magnetic Topology of AR13664 Leading to Its First Halo CME

In the first half of May 2024, the solar active region (AR) NOAA 13664 was responsible for generating the strongest geomagnetic storm in over 20 years through an enhanced production of coronal mass ejections (CMEs). A key factor in this production was the complex magnetic topology of AR13664. In this work, we investigate the region's magnetic topology related to the production of its first halo CME on May 8th. This is achieved by combining different observations of magnetic topology based on photospheric magnetic helicity and winding signatures and nonlinear force-free field extrapolations, together with Atmospheric Imaging Assembly observations at different wavelengths. We present evidence that the first halo CME, and its associated X1.0 flare, was created by an emerging twisted flux tube within AR13664, following the general picture of the standard flare model. The coincidence of the first large magnetic winding signature with the start time of the X1.0 flare provides the onset time for the CME as well as the period of enhanced eruptive activity of the region—04:36 UT on May 8th.