In our solar system, solar flares and coronal mass ejections (CME) are the most spectacular eruptive activities. Large solar flares and CMEs could bring us disastrous space weather, destroy our satellite and navigation system, and cause a large-scale blackout on Earth. Recently, a research team led by Dr. Ting Li of the National Astronomical Observatories of Chinese Academy of Sciences (NAOC) discovered important factors that govern the eruptive character of large solar flares. And the research result was published on the Astrophysical Journal in September 2020.

“We have known the phenomenon called ‘solar flare’ ever since the first observation by Carrington and Hodgson in 1859. We have learned a great deal in the century and a half that have passed since, but these basic questions remain with us: What powers a solar eruption? What triggers it? What is the relationship between flares and CMEs?” said Dr. Ting Li, the paper author, “These questions continue to occupy us as we bring ever-increasing instrumental and computational capabilities to bear on the problem.”

Li and her team used the 10 years observations from the satellite of Solar Dynamics Observatory (SDO) during 2010-2019 and established the largest flare database to date. The database includes 322 large solar flares and involves the eruptive character of each large flare (if the flare is associated with a CME or not).

“Solar active regions (AR) are the cradle producing solar flares and CMEs. We found that the total magnetic flux of ARs is a key parameter in governing the eruptive character of large flares. This means that an AR containing a large magnetic flux has a lower probability for the large flares it produces to be associated with a CME.” said Dr. Ting Li.

Their findings are interesting in two aspects:

For the solar case, as it means that for the strongest space weather effects (which are predominantly due to the CME rather than the flare), we cannot simply extrapolate that the space weather effects will be increasingly stronger for flares produced by large ARs present on the Sun.

Second, it has implications for the stellar case: we may speculate that in case of the much larger ARs (stellar spots) that are needed to produce the reported “superflares” on solar-type stars, the flares are probably not associated with CMEs. This may provide an explanation why the detection of stellar CMEs is rare.

This work was a collaboration with the School of Physics and Materials Science at the Anhui University, School of Atmospheric Sciences at the Sun Yat-sen University, and the Institute of Physics & Kanzelh, the Observatory for Solar and Environmental Research at University of Graz in Austria.

Figure. Relations of the eruptive character of large solar flares with AR magnetic flux and area. (Credit: Ting Li)

This paper can be accessed at https://iopscience.iop.org/article/10.3847/1538-4357/aba6ef