arXiv subjects

LiDong Xia

Publications and source records attributed to LiDong Xia.

3 recordsLinked to original sources

arXiv2025

Enhanced Non-Thermal Line Broadening inside Coronal Cavities above Solar Prominences revealed by Spectral Imaging CoronaGraph

Coronal cavities, often associated with prominences, are crucial structures in understanding coronal heating and the eruption mechanism of Coronal Mass Ejections (CMEs). Previous studies have identified their lower density, higher temperature, and flux rope structures. However, spectroscopic observations are still relatively scarce. In this study, we utilize the newly developed Spectral Imaging Coronagraph (SICG), Chinese H$α$ Solar Explorer (CHASE), and AIA/SDO to analyze the morphology, temperature, Doppler shift, and non-thermal velocity of two coronal cavities observed on November 13, 2024. We find that coronal cavities are distinctly visible in SICG \ion{Fe}{14} 5303~Å and AIA 193~Å, whereas they are nearly absent in SICG \ion{Fe}{10} 6374~Å and AIA 171~Å. The spectroscopic measurements show that the two coronal cavities display asymmetric, ring-like structures in the \ion{Fe}{14} 5303~Å Doppler shift maps. The non-thermal velocities inside coronal cavities are significantly higher than those of the surrounding streamer areas. In addition, the core regions of coronal cavities, located directly above the prominences, exhibit the highest non-thermal velocities and Doppler velocities. Our results suggest the presence of waves and turbulence in coronal cavities, which are likely more intense than those in the adjacent streamer regions. We suggest that the interaction and exchange between the cold, dense prominence materials and the hot, low-density coronal materials are the main drivers of the waves and turbulence inside coronal cavities.

astro-ph.SR↗

arXiv2020

The high helium abundance and charge states of the interplanetary CME and its material source on the Sun

Identifying the source of the material within coronal mass ejections (CMEs) and understanding CME onset mechanisms are fundamental issues in solar and space physics. Parameters relating to plasma composition, such as charge states and He abundance (\ahe), may be different for plasmas originating from differing processes or regions on the Sun. Thus, it is crucial to examine the relationship between in-situ measurements of CME composition and activity on the Sun. We study the CME that erupted on 2014 September 10, in association with an X1.6 flare, by analyzing AIA imaging and IRIS spectroscopic observations and its in-situ signatures detected by Wind and ACE. We find that during the slow expansion and intensity increase of the sigmoid, plasma temperatures of 9 MK, and higher, first appear at the footpoints of the sigmoid, associated with chromospheric brightening. Then the high-temperature region extends along the sigmoid. IRIS observations confirm that this extension is caused by transportation of hot plasma upflow. Our results show that chromospheric material can be heated to 9 MK, and above, by chromospheric evaporation at the sigmoid footpoints before flare onset. The heated chromospheric material can transport into the sigmoidal structure and supply mass to the CME. The aforementioned CME mass supply scenario provides a reasonable explanation for the detection of high charge states and elevated \ahe\ in the associated ICME. The observations also demonstrate that the quasi-steady evolution in the precursor phase is dominated by magnetic reconnection between the rising flux rope and the overlying magnetic field structure.

astro-ph.SR↗

arXiv2018

Helium abundance and speed difference between helium ions and protons in the solar wind from coronal holes, active regions, and quiet Sun

Two main models have been developed to explain the mechanisms of release, heating and acceleration of the nascent solar wind, the wave-turbulence-driven (WTD) models and reconnection-loop-opening (RLO) models, in which the plasma release processes are fundamentally different. Given that the statistical observational properties of helium ions produced in magnetically diverse solar regions could provide valuable information for the solar wind modelling, we examine the statistical properties of the helium abundance (A_He) and the speed difference between helium ions and protons (v_alpha,p) for coronal holes (CHs), active regions (ARs) and the quiet Sun (QS). We find bimodal distributions in the space of A_He and v_alpha,p/v_A (where v_A is the local Alfven speed)for the solar wind as a whole. The CH wind measurements are concentrated at higher A_He and v_alpha,p/v_A values with a smaller A_He distribution range, while the AR and QS wind is associated with lower A_He and v_alpha,p/v_A, and a larger A_He distribution range. The magnetic diversity of the source regions and the physical processes related to it are possibly responsible for the different properties of A_He and v_alpha,p/v_A. The statistical results suggest that the two solar wind generation mechanisms, WTD and RLO, work in parallel in all solar wind source regions. In CH regions WTD plays a major role, whereas the RLO mechanism is more important in AR and QS.

astro-ph.SR↗