BS, Astronomy (DII), Nanjing University
CMEs are massive eruptions of solar plasma that propagate in the interplanetary space. They can cause adverse geomagnetic disturbances if are Earth-directed. So we would like to accurately predict their arrival time at the Earth, with a simple and fast kinematics method (rather than time-consuming yet not-so-accurate simulations). We make a statistical study of 21 Earth-directed CMEs by reconstructing their initial speeds with the Graduated Cylindrical Shell model based on multi-perspective images and formulating their interplanetary motions with the drag force model. We show significantly imporved prediction results with an error of only 6.8 hours. Thus, it provides a neat method of space weather forecast of 1–5 days following the occurrence of CMEs.
Plasma diagnostics and elemental abundance measurements are crucial to help us understand the formation and dynamics of the solar wind. So we use a theoretical solar wind model to study the effect of NEI on plasma diagnostic techniques applied to line intensities emitted by the fast solar wind. We find that NEI almost always changes the spectral line intensities with up to 120% difference for the lighter elements and for higher charge states of Fe even below 1.5 solar radii (Rs). The measured plasma density, temperature, and differential emission measure are only slightly affected by NEI. However, NEI significantly affects the first-ionization potential (FIP) bias and abundance ratio measurements, producing an error of up to a factor 4 at 1.5 Rs for the Mg-to-Ne, Fe-to-S, and Ar-to-Fe ratios when EI is assumed. We conclude that it is very important to consider the NEI effect when spectral line intensities are synthesized and the FIP bias and elemental abundance are measured.
Shi, T., Wang, Y. K., Wan, L., Cheng, X., Ding, M. D. & Zhang, J. 2015, ApJ, 806, 271 (link)
Wan, L., Cheng, X., Shi, T., Su, W. & Ding, M. D. 2016, ApJ, 826, 174 (link)
Shi, T., Landi, E., Manchester, W., IV 2019, ApJ, 882, 154 (link)