A few major geoeffective flares and CMEs occurred in May 2024. HMI magnetic field data were used to examine how the flares occurred and why they became geoeffective.
The coronal magnetic field evolution of the AR 11429 was simulated using time-dependent magneto-friction model. The model reproduced the magnetic structure that has remarkable correspondence with the spatial characteristics in coronal extreme ultraviolet images.
Magnetic power spectra were calculated using MDI and HMI data for two solar cycles. It is found that the sizes of the magnetic networks do not show a cycle dependence, but the power-law indices estimated from the active region and network sizes show an anti-correlation with the sunspot numbers.
Is the solar meridional circulation profile single-, double-, or multiple-cell? At least, a constraint of equatorward angular momentum transport by meridional circulation favors the double-cell structure, although the inversion with a constraint of mass conservation favors single cell.
A surface flux transport model, using HMI-observed global magnetic field and active regions as inputs, with different polar meridional-flow profiles simulates the magnetic field in the polar caps. The simulation is then compared with Hinode-observed polar magnetic fields. The result supports an existence of counter cells above 70-degree latitude in each hemisphere.
The Sun’s near surface shear layer (NSSL) is characterized by using HMI ring-diagram results. It is found the NSSL is composed of three distinct layers: a deeper larger region with a small shear, a narrow middle layer with a strong shear, and a layer very close to the surface.
A new method was developed to identify white-light flares (WLFs) observed in SDO/HMI continuum intensity. The new method is able to identify around 30% of C-class flares (and more percentage in stronger flares) having white light brightening associated with them, greatly expanding the total number of WLFs observed by HMI. The increased number of detections would help a statistical study of the properties of WLFs.
This study analyzes a few properties of evolving bipolar magnetic regions: separation of polarities, tilt angles, and tilt angle and flux relations. The analysis supports that the bipolar regions form from thin-flux tubes and Coriolis force plays an important role in forming the regions.
NOAA active regions 13664/8, the solar source region responsible for the May 2024 extreme geomagnetic disturbances that caused the largest geomagnetic storm since 2003, broke the record of magnetic flux emergence rate in the SDO era.
The advective flux transport model, coupled with a random active region generator, predicts that the solar activity will peak in the northern hemisphere around August 2024, and peak in the southern hemisphere around February 2025.