Relationship Between Solar Wind Parameters Observed At 1 AU And Their Source Region Properties

The space environment near the Earth is mainly influenced by the solar activities. For example, the solar wind is an important medium through which the Sun can impact the near-Earth space environment. However, when the geoeffectiveness of the solar acitivities were discussed, most studies focused on the effects caused by the solar dramtic eruptions such as coronal mass ejections (CMEs) and flares, while those driven by the high-speed streams (HSSs) with their source region in the coronal hole and associated corotating interaction regions (CIRs) are seldom discussed. Nervertheless. at least during the descending phases and the minima of solar cycles, the HSSs and CIRs are the main sources and drivers of catastropic events in the Earth's magnetosphere. Therefore, it is important to study the relationship between solar wind parameters observed at 1AU and their source region properties, which may be further used to predict the solar wind parameters at 1 AU. In this thesis, we will use the PFSS and CSSS models respectively to extrapolate the coronal magnetic fields and identify the relevant source regions of selected solar wind streams. Then we deduce the parameters such as bightness and magnetic fields in the source regions using EIT full disk images and the extrapolated magnetic field data. Finally, we analyse the correlation of solar wind speeds at 1AU and relevant parameters in the source regions. The main findings can be summarized as follows:1) Although the PFSS (Potential Field Source Surface) model and CSSS (Current Sheet Source Surface) model are used to calculate the coronal magnetic fields with a series of assumptions, the source regions of the high-speed streams identified by these extrapolated magnetic fields generally coincide with the coronal hole regions observed on the disk by EIT at the 284 passband. And in most cases, an open field line on the source surface of the two models can be traced back to the same location (footpoint) on the solar disk. The result demonstrates that the extrapolated coronal magnetic fields can be used for our further study. 2) The averaged net flux of the photospheric magnetic fields in all selected coronal holes is non-zero, i.e., one polarity of magnetic fields dominates there. The ratio of the flux of the dominated polarity fields to the total flux of the magnetic fields is larger in the coronal holes with smaller areas. We also found that the coronal hole regions seen in EIT images become brighter with increasing magnetic field strength. We confirm previous results that the solar wind velocity increases with increasing area of the cornal holes and with decreasing areal expansion factor of the high-speed stream tube. Moreover, our analysis shows a close correlation between the solar wind velocity and the brightness of the coronal holes seen in EIT images. The correlation coefficient is negative, indicating that a darker coronal hole has a faster solar wind stream at 1 AU.3) We define a parameter that may represent the variation of the coronal brightness, namely, ISR=∑(1/(?))/N. where b is the brightness at every pixel and N is the number of pixels. We found that the parameter ISR deduced from the source regions of the solar wind has a good correlation with the corresponding solar wind velocity at different phases of solar cycles except for the solar maxima. Meanwhile, the parameter 1/ISR shows a good correlation with radial magnetic field strength over the whole solar cycle. Because 1/ISR is somehow related to the electron density of the source regions, this may imply that the average electron density is approximately proportional to the magnetic field strength at solar wind source regions.