Dynamics of Subsurface Flows in Solar Active Regions during the 2024 Gannon Storm

 In May 2024, the Sun produced a series of intense flares and CMEs, primarily from NOAA Active Regions (ARs) 13663 and 13664, which were visible on the solar disk at that time. The image shows a full-disk magnetogram from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory on May 6, 2024, highlighting both regions. While surface and coronal observations reveal much about these eruptions, active regions are rooted deep within the Sun. To explore the hidden dynamics beneath them, we use a local helioseismic technique that uses sound waves traveling through the solar interior to measure horizontal flows beneath these active regions.  

It is found that the flow divergence remained mostly negative throughout the observing period for all active regions, indicating that horizontal flows converge toward areas of strong magnetic field. It is also observed that the amplitudes of vorticity and kinetic helicity tended to increase before a series of flares occurred. After these flare episodes, the amplitudes decreased, only to rise again ahead of subsequent eruptions. This behavior was consistent across different depths below the surface, with deeper layers generally showing stronger signals. The Normalized Helicity Gradient Variance (NHGV), which captures how kinetic helicity varies with time and depth showed  that NHGV typically increased at least a day before flares. Notably, about 81% of the observed flares occurred either on the day NHGV reached a local  maximum or on the following day. Together, these results highlight the importance of subsurface dynamics in shaping the evolution and eruptive potential of solar active regions. 

This study was published in The Astrophysical Journal (Authors: B. Lekshmi, Sushanta Tripathy, Kiran Jain, and Alexei Pevtsov)  

https://iopscience.iop.org/article/10.3847/1538-4357/ade2e3