Researchers from the Chinese Academy of Sciences, led by Yue Zhou and Li Feng, have published a study in the journal Astronomy & Astrophysics that sheds light on the relationship between solar shock waves and solar energetic particles (SEPs), which can impact space weather and have implications for space-based and terrestrial energy infrastructure.
The study investigates how the spatial and temporal evolution of shock properties influences the distribution and energy spectra of SEPs. By combining a steady-state solar wind simulation with three-dimensional reconstructions of shock surfaces using multi-view observations, the researchers derived key shock parameters such as normal speed, oblique angles, compression ratio, and Alfven Mach number. These parameters were then compared with in situ proton intensities and peak spectra to establish a link between shock evolution and SEP characteristics.
The researchers found that the shock nose, the leading edge of the shock wave, exhibited higher particle acceleration efficiency. This region had the largest normal speed, compression ratio, and supercritical Alfven Mach number, which are all indicative of more effective particle acceleration. In contrast, the flanks of the shock wave showed a delayed transition to supercritical Alfven Mach number and weaker acceleration efficiency.
The study also revealed that the earliest and most rapid proton enhancement observed by the STEREO-B spacecraft correlated with efficient shock acceleration and prompt magnetic connectivity to the shock. Spectral analysis indicated that the proton energy spectra were consistent with predictions from the relativistic diffusive shock acceleration (DSA) model. The initial shock acceleration began at a distance of about 1.4 to 5 solar radii from the Sun’s surface and contributed to the widespread longitudinal distribution of SEPs.
The longitudinal dependence of SEP intensity and spectral variations was found to arise from the combined influence of three-dimensional shock properties, magnetic connectivity, and particle transport processes. The agreement between in situ proton indices and relativistic DSA estimations supports the role of DSA in this SEP event and provides valuable insights into the early-stage acceleration at the source region.
Understanding these processes is crucial for improving space weather forecasting, which can help protect space-based assets such as satellites and the energy infrastructure on Earth that is vulnerable to solar storms. By enhancing our knowledge of how solar shocks accelerate particles, we can better predict and mitigate the impacts of solar energetic particles on technological systems.
Source: Astronomy & Astrophysics
This article is based on research available at arXiv.