Solar flares suddenly emit strong electromagnetic radiation from the solar surface and its atmosphere and are expelled plasma and energetic particles in interplanetary space. Since large solar flares can cause severe space weather disruptions on Earth, their occurrence must be predicted to mitigate their effects. However, because the mechanism of initiation of solar flares is unclear, most methods for predicting flares have relied on empirical methods.
The research team led by Professor Kanya Kusano (Director of the Institute for Space-Earth Environmental Research, Nagoya University) recently succeeded in developing the first physics-based model that can accurately predict upcoming major solar flares. The work was published in the journal science on July 31, 2020.
The new method of flare prediction, the kappa scheme, is based on the theory of “double arc instability”, a magnetohydrodynamic (MHD) instability that is triggered by magnetic reconnection. The researchers assumed that a small reconnection of magnetic field lines could create a double-arc magnetic field (m-shape) and trigger the onset of a solar flare (Figure 1). The kappa scheme can predict how a small magnetic reconnection will trigger a large flare and how a large solar flare can occur.
The predictive model was tested on approximately 200 active regions during solar cycle 24 from 2008 to 2019 using data obtained from NASASolar Dynamics Observatory (SDO) satellite. With a few exceptions, the kappa scheme has been shown to predict the imminent solar flares as well as the exact location where they will occur (Figure 2). The researchers also discovered that a new parameter – the “twisting magnetic flux density” near an inversion line with magnetic polarity on the solar surface – determines when and where solar flares are likely to occur and how large they are likely to be.
Previous methods of predicting flares relied on empirical relationships in which the previous day’s predictions tended to persist until the next day, even if the flare activity changed. In contrast, the kappa scheme predicts large solar flares through a physics-based approach, regardless of previous flare activity. While implementing the scheme in real-time operational forecasting requires much more work, this study shows that the physics-based approach may open a new direction for research on flare forecasting.
Reference: “A physics-based method that can predict upcoming major solar flares” by Kanya Kusano, Tomoya Iju, Yumi Bamba and Satoshi Inoue, July 31, 2020, science.
DOI: 10.1126 / science.aaz2511