| 其他摘要 | The sun is the closest star to us and the only one that can be observed closely. It provides a lot of observational data for studying the law of stellar evolution and the evolution of plasma in the corona. Usually, the solar activity events we observed may be composed of a variety of dynamic processes. Due to the limitations of observation conditions and instruments, we do not really understand the physical properties of the solar atmosphere and its evolution. This means that a deeper understanding of these dynamic processes taking place in the solar atmosphere requires a combination of observational and theoretical analysis. The solar corona consist of highly ionized, low-density, hot plasma with temperature of million degrees. The coronal green line (530.3nm) gives rise to the strongest forbidden line emission in the coronal spectrum, which is formed by the forbidden transitional process ( 2P3/2 - 2P1/2) in the 3s23p ground configuration of ion Fe XIV. The green line emission was firstly discovered from solar eclipse observations, now it has been popularly used for the regular observations by coronagraphs. Its high temperature and brightness make it a useful spectral line has been used as longterm powerful diagnostic tools for studying the coronal configurations and hot plasma dynamics. Based on the construction of the first Coronagraph observatory in China, we carry out the construction and observation of the Coronagraph, the analysis and research of the coronal green line. First start the site selection of Coronagraph observation stations in China. A batch of candidate sites suitable for ground-based Coronagraph observation are obtained through preliminary survey and measurement. According to the analysis of cloud cover, rainfall and sunshine hours from the national satellite meteorological data, it is confirmed that Lijiang Astronomical Observatory has the advantage of building the Coronagraph observation station, and held more than two years of the measurements of corona observation conditions. In 2013, the first Coronagraph for routine observation was completed. Subsequently, the Coronagraph observation system, high-precision tracking system, focusing system, automatic monitoring device for primary mirror finish, heliocentric intensity acquisition system, flat-field acquisition mode, data calibration system and optical filter system were developed and upgraded. At the same time, a ground-based Coronagraph high-altitude testing center was built. We have shown the close relationship between the brightness in the coronal green line and the extrapolated magnetic field intensity using data from the Lijiang coronagraph and the potential field source-surface (PFSS) model. The coronal magnetic fields are calculated from the PFSS model based on the synoptic magnetograms taken by Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) spacecraft, and we construct a two-dimensional image of the magnetic field intensity in the plane of the sky (POS) from 1.03 to 1.3 solar radii above the solar center. We derive the correlation coefficients between the coronal brightness and the magnetic field intensity for different heights of coronal layers. We further use a linear combination of a Gaussian and a quadratic profile to fit the correlation coefficients distribution, finding a largest correlation coefficient of 0.82 near 1.1 R⊙ (solar radii) where is almost the top of the closed loop system. We also investigate the correlation with extended heliocentric latitude zones and long period of one Carrington Rotation, finding again that the maximum correlation coefficient occurs at the same height. For the small closed loop system identified, the correlation coefficient distributions crossing and covering the loop are calculated. It is the first time for us to find that the correlation coefficients are high (all are larger than 0.80) at the loop-tops and showing poor correlation coefficients with some fluctuations near the feet of the coronal loops. Furthermore, we use the green-line data by the Lijiang Lyot coronagraph and the EUV data from the SDO/AIA instruments to make the direct comparisons and studies, based on two algorithms developed to extract particular features in low corona. It is found that, among the correlation coefficients obtained between the intensities of 530.3 nm and the EUV lines, the coefficients between the coronal green line and the 21.1 nm wavelength for different coronal structures and limb locations always keep the highest values (ranging from 0.89 to 0.99), which has not been reported before. This result can help to connect the physical processes observed in different heights in the corona by precisely tracking the bright loops or other features observed in 5303 Å above the limb down to the correct surface locations revealed by the 21.1 nm data. Furthermore, the ground-based observations of the coronal green line and the space-based EUV observations at 21.1 nm can complement each other when there is a need, which is important for the long-term study of solar cycles. Our findings indicate that, for the heating of the low-laltitude closed loops, both DC (dissipation of currents) and AC (dissipation of Alfven and magnetosonic waves) mechanisms should act simultaneously on the whole closed loop system while the DC mechanisms dominate in the loop-top regions. Since the maximum correlation coefficient appears around the top of the coronal arched structures, if the closed coronal arched structure is opened for some reason, then the hot plasma confined in the dense loop system will be released and accelerated by the coronal magnetic field nearby. The height 1.1R⊙ should be important as the site of the source for the origin of the low-speed solar wind from the low solar corona. We need to use more coronal green line data to derive reliable scaling laws relevant to coronal heating and to test various theoretical models for coronal magnetic fields for next studies. Due to the failure of the space coronal green line observation instrument, there's been no coronal green line observations available from space till now. The AIA 21.1 nm observations, together with the other EUV data taken successively from space, can be conducive to fill in the ``missing'' observational gaps for the green line data. |
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