A robust, calibrated method for measuring sunspot areas from SOHO/MDI and SDO/HMI full-disk images enables a consistent, observer-independent, long-term catalogue of daily sunspot areas, revealing detailed patterns of sunspot group area evolution and solar cycle variability.
Each solar active region (AR) has its unique shape, size, and lifetime. In this work, the authors developed a method to ‘average’ bipolar ARs by normalizing their size, orientation, and timing, thereby revealing the typical properties of an AR and its evolutionary pattern.
Strong acoustic scatterers are found beneath sunspot umbrae and penumbrae using the phase-correlation holography method. These scatterers indicate the fragmentation of magnetic flux, as suggested by Eugene Parker in the 1970s.
Eruptive and non-eruptive solar flares were investigated based on an analysis of electric current neutralization and torus instability. Combined analysis of these factors offers a more reliable prediction of eruptive events than relying on either one alone.
The analysis of magnetic fields and electrical currents indicates that a specific configuration – currents in opposite magnetic regions flowing in the same direction and peaking concurrently – might create favorable conditions for the magnetic reconnection process that powers solar flares.
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.
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.
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.
A survey of how many off-limb white-light events were observed by the SDO/HMI was conducted, and a catalogue is published online with real-time updates.
An analysis of two active regions shows that differently evolving ARs may produce major eruptive flares even when, in addition to the accumulation of significant free magnetic energy budgets, they accumulate large amounts of both left- and right-handed helicity without a strong dominance of one handedness over the other.