| dc.description.abstract | This thesis analyzes the characteristics of 181 low to mid-latitude coronal holes between June 2010 and January 2021 using SDO/AIA 193 Å solar image, SDO/HMI magnetogram, and OMNI database (solar wind data at 1 AU). The analyzed features include the impact of coronal hole on high-speed streams (ICH-HSS), which represents the influence of coronal hole on the near-Earth solar wind. It is calculated based on the coronal hole area and the weighting in the spatial distribution function. Additionally, the study examines the position, magnetic field strength, magnetic flux, and their correlations with solar wind speed.
The research is divided into two main parts: the analysis of coronal hole events′ characteristics and the investigation of long-lived events′ evolution. The analysis of event characteristics reveals a positive correlation between ICH-HSS and solar wind speed (correlation coefficient r = 0.53-0.57). Furthermore, the coronal hole magnetic flux shows a correlation with solar wind speed (r = 0.41-0.45), while the correlation between ICH-HSS and magnetic field strength is positive but not significant (r = 0.25-0.45). The magnetic field strength of coronal holes is found to be unrelated to solar wind speed (r < 0.25). Over the 10-year analysis period, the variation trend of magnetic field strength and magnetic flux in coronal holes is consistent with those of sunspot numbers. ICH-HSS exhibits a similar trend but with a delay of 1-2 years compared to sunspot numbers. On the other hand, solar wind speed does not display the same variation trend as sunspot numbers. However, the study reveals the presence of long-lived coronal holes. Seven coronal holes that were observed at least 5 times during the study period dentified. The evolution of ICH-HSS in these long-lived events corresponds to the findings reported by Heinemann et al. (2018a) regarding the evolution of coronal hole area. Each coronal hole exhibits a growing phase, a maximum phase, and a decaying phase, but the evolution process varies case by case. In addition to the evident evolution of ICH-HSS, the magnetic field strength, magnetic flux, and solar wind speed also demonstrate similar trends throughout the evolution process.
In this study, 59 events were found lacking corresponding solar wind speed data among 181 analyzed events. This discrepancy may be attributed to factors such as coronal mass ejections (CMEs) and the interplanetary space environment. Further discussions will be conducted to address these specific events. | en_US |