Recurrent geomagnetic storms

Recurrent geomagnetic storms are associated with large coronal holes (CH). As Sun rotates, the same area of open magnetic field is brought up to face Earth every about 26 days. A large CH that was observed crossing solar central meridian early this week existed for several solar rotations. Upper row of images show solar corona observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) on 19 June, 15 August, and 11 September 2025. A large CH is seeing near central meridian on these days. In all cases, about four days later, there were moderate geomagnetic storms associated with this CH. Lower panel shows Kp (ap) index from the International Service of Geomagnetic Indices (ISGI)  database. It appears that a geomagnetic storm associated with this CH is now in development.