NOAA sunspot records from Cycles 22 to 24 reveal that the Sun’s north-south asymmetry is concentrated in activity nests. HMI observations show nesting tracks each hemisphere’s quasi-biennial oscillation and changes in the large-scale magnetic field.
HMI data from Solar Cycle 24 data are used to determine how often the Sun emerges sunspots in activity nests. It is found that the Sun shows moderate nesting behavior with 41% (48%) of AR magnetic flux found in northern (southern) hemisphere located in nests. The maximum number of nests are found with slightly prograde rotational velocities, and the nesting behavior is asymmetric in the hemispheres.
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.
Compactness is one geometric property of a sunspot group that has not yet been systematically quantified. We calculate the compactness of a small sample of δ-spots and β-spots using a minimum bounding circle. On average, the δ-spots are found to be more than twice as compact as the β-spots.
Apparent 3-min waves observed inside sunspot umbrae are modeled as excited about 1000 to 2000 km beneath sunspots’ surface.
Where does a sunspot’s penumbra start to form, on the same side or the opposite side of its opposite-polarity sunspot? When does Evershed flow start to appear, before or after the penumbral formation? These questions are answered through analyzing selected samples observed by the HMI.
AR12192, the largest active region in Solar Cycle 24, produced 6 X-class flares, but none of them were associated with a CME. However, a much weaker flare, of M4.0-class, was associated with a CME. Magnetic field and morphological changes are analyzed during these flares to understand why this is the case.
Helioseismic far-side images are compared with the STEREO-AIA EUV observations, and a reliability of the helioseismic images is assessed.
We quantify the emergence and decay rates of ten bipolar active regions using vector magnetic field data from HMI. Our results, placed in context with other observational and modeling results in the literature, confirm a trend that higher flux regions emerge faster and the rate is dependent on the total flux of that region.