(a) The pair of sunspots S1 and S2 with the inner and outer limits of the penumbra, (b) the mapping of the longitudinal magnetic fields of the pair, and (c) the evolution of the rotation angle of the sunspots . Credit: The Astrophysics Journal (2024). DOI: 10.3847/1538-4357/ad063e
Scientists studying sunspots have found important clues about the magnetic characteristics of their decay that will help understand the evolution and real origin of these mysterious magnetic phenomena. The results are published in The Astrophysics Journal.
Understanding sunspots is crucial to understanding the solar cycle, the approximately 11-year periodic change that alters the sun’s energy output and the frequency and intensity of the solar flares it sends into space and which can negatively influence satellites and power grids on Earth. (The solar “cycle” can last eight to 14 years.)
Sunspots look pretty simple from a distance, but they are complex areas where sunlight is trapped by twisted magnetic fields. These are temporary regions of reduced temperature that appear as dark spots on the sun’s surface, where restricted magnetic flux suppresses the convection that brings the sun’s internal heat to the surface. A sunspot is about the size of Earth and often comes in pairs.
Sunspot decay is also not well understood. The central shadow of a sunspot is dark and has the strongest magnetic fields; the surrounding penumbra, which may surround several sunspots, is brighter (but still darker than the sun) and is composed of elongated regions called penumbra filaments.
Full-fledged sunspots are surrounded by convective granular regions, which can form supergranules called fluke cells, mainly non-magnetic annular regions. Fluke cells extend 10 to 20 million meters beyond the limit of sunspot penumbra.
Inside the moat cell is the moat flow, a slow radially outward flow of plasma, directed away from the center of the sun, that is, away from the sunspot. Then, within these movements are small moving magnetic features (MMFs) that migrate away from the sunspot and rely on magnetic fields in the sunspot’s penumbra.
Chinese scientists observed two adjacent sunspots for seven days in 2022, with data taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (launched in 2010) and focused on the relationship between the decay of the magnetic flux of the two sunspots and transport. of the magnetic flux by the MMF. (“Magnetic flux” can be thought of as the exit or entry of magnetic field lines through a bounded area.)
The sunspots rotated around each other about 13 degrees per day for the first five days, then the rotation stopped. Determining the limits of umbra and penumbra based on changes in solar intensity relative to the average of the quiet solar region, they observed horizontal velocity fields of the plasma, which in turn gave estimates of the magnetic flux of MMF.
The pair’s sunspots each decayed at a rate of about 15 million km.2 per day, an area the size of Antarctica. As a result, the rate of decrease in magnetic flux across the sunspot is of the order of 10.20 maxwells per day, where a maxwell (Mx) is the unit of magnetic flux, equal to one gauss per cm2. (The Earth’s magnetic field, although variable, is approximately 0.2 to 0.6 gauss.)
In this setting, the MMFs, the small-scale magnetic volumes that move radially away from their sunspot, had a size of about 2 arcseconds as seen from Earth and moved at a speed of about 400 meters per second.
The relationship between the loss of magnetic flux due to a decaying sunspot and MMFs still remains mysterious. But the quantitative parameters measured here establish that “the formation of moving magnetic features depends on penumbral magnetic fields,” authors Yang Peng and Zhike Xue, respectively of the Yunnan Observatory of the Chinese Academy of Sciences and from the University of China. Chinese Academy of Sciences.
“Our results show that a large number of MMFs will also be generated in the non-penumbra region, and that vertical MMFs (MMFs whose magnetic field is vertical) in this region have significantly increased compared to those around the penumbra, which is closely related to the bare shade in the granule.
These observations suggest that MMFs with vertical magnetic fields are closely related to sunspot decay, and that most MMFs in the space region between the two sunspots may originate directly from the sunspot shadows.
“The results provide possible clues to the real origin of monetary funds,” Peng and Xue said.
More information:
Yang Peng et al, The disintegration of two adjacent sunspots associated with moving magnetic features, The Astrophysics Journal (2024). DOI: 10.3847/1538-4357/ad063e
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