Research

I will present my first-authored papers here. For more details please see my Google Scholar page. I also attach the codes that are used in each work at the end of each abstract. Please star them if you find them helpful!

The Alpha-proton Differetial Flow in the Young Solar Wind: From Sub-Alfvénic to Super-Alfvénic

Authors: Hao Ran, Ying D. Liu, Chong Chen, Parisa Mostafavi
Published in: The Astrophysical Journal, 963, 82, 2024
Abstract: Data obtained from Parker Solar Probe (PSP) since 2021 April have shown the first in situ observation of the solar corona, where the solar wind is formed and accelerated. Here, we investigate the alpha-proton differential flow and its characteristics across the critical Alfvén surface (CAS) using data from PSP during encounters 8–10 and 12–13. We first show the positive correlation between the alpha-proton differential velocity and the bulk solar wind speed at PSP encounter distances. Then we explore how the characteristics of the differential flow vary across the CAS and how they are affected by Alfvénic fluctuations including switchbacks. We find that the differential velocity below the CAS is generally smaller than that above the CAS, and the local Alfvén speed well limits the differential speed both above and below the CAS. The deviations from the alignment between the differential velocity and the local magnetic field vector are accompanied by large-amplitude Alfvénic fluctuations and decreases in the differential speed. Moreover, we observe that Vαp increases from MA < 1 to MA ~ 2 and then starts to decrease, which suggests that alphas may remain preferentially accelerated well above the CAS. Our results also reveal that in the sub-Alfvénic solar wind both protons and alphas show a strong correlation between their velocity fluctuations and magnetic field fluctuations, with a weaker correlation for alphas. By contrast, in the super-Alfvénic regime the correlation remains high for protons, but is reduced for alphas.
See the paper here. The codes used in this work are shared here.

Relationship between Successive Flares in the Same Active Region and SHARP Parameters

Authors: Hao Ran, Ying D. Liu, Yang Guo, Rui Wang
Published in: The Astrophysical Journal, 937, 43, 2022
Abstract: A solar active region (AR) may produce multiple notable flares during its passage across the solar disk. We investigate successive flares from flare-eruptive ARs, and explore their relationship with solar magnetic parameters. We examine six ARs in this study, each with at least one major flare above X1.0. The Space-weather HMI Active Region Patch (SHARP) is employed in this study to parameterize the ARs. We aim to identify the most flare-related SHARP parameters and lay foundation for future practical flare forecasts. We first evaluate the correlation coefficients between the SHARP parameters and the successive flare production. Then we adopt a Natural Gradient Boost (NGBoost) method to analyze the relationship between the SHARP parameters and the successive flare bursts. Based on the correlation analysis and the importance distribution returned from NGBoost, we select the eight most flare-related SHARP parameters. Finally, we discuss the physical meanings of the eight selected parameters and their relationship with flare production.
See the paper here. The codes used in this work are shared here.