The Studies On Observational Characteristics And Physical Mechanism Of Solar Small-scale Structures

Solar magnetic structures in the solar diferent atmospheres exhibit a varietyof spatial scales. Magnetic felds in the lower solar atmosphere have structureon the smallest observable scales (magnetic element), up to the difraction limitof the best telescopes all over the world. Theoretical arguments and simulationsindicate that there is magnetic structure well beyond what we can be observednow or in the forseeable future. Small-scale magnetic structures on the solaratmospheres can be detected almost everywhere, but they are not absolutelyuniform distribution in the solar surface. Aside from they have several basicfeatures, such as small scale, changing shape and shorter lifetime, they also havemany other characteristics, e.g. rapid emergence, evolution and disappearance,they can provide most of the energy sources of solar radiation. These factsmake the small-scale magnetic structures in the solar atmospheres potentiallyimportant to understand the solar global/local dynamo theory, chromosphericand coronal heating, the source and acceleration of the fast solar wind, emergenceand cancellation of magnetic flux, etc., which are not fully understood today.During the last fve decades, studies on the small-scale magnetic structuresare one of the most important topics in solar physics. Although investigations ofboth observational characteristics and physical mechanism have achieved a sig-nifcant progress, while a clear majority of high-resolution observations derivedfrom medium-aperture solar telescopes can not publically downloaded. At thebeginning of2011, the New Vacuum Solar Telescope (NVST), located at FuxianSolar Observatory of Yunnan Observatories, was successfully established. Thehigh-performance photospheric and chromospheric observational equipments, themulti-channel observations terminals, polarimeter and multi-wavelength spec-trometer open a best opportunity to study the small-scale magnetic structures.This thesis takes the magnetic bright points and polar faculae as the subjectinvestigated, both of them have the kilo-Guass magnetic feld strength. We per-form a panoramic and depth exploration on both observational characteristics and statistical properties of these two small-scale structures.The frst part of the thesis is an overview of background, status and sig-nifcance, from which the motivation, contents and objectives of our work isintroduced. In the second part, we use the high-resolution observational dataderived from NVST at TiO-band on October29,2012and May21,2013to ob-tain the size, intensity, velocity and shape of magnetic bright points, and thenwe will analyse and discuss the observational characteristics of these two datasets. For identify the magnetic bright points, an automatic algorithm, employingLaplacian and morphological dilation technique, is proposed. Analysis resultsindicate that our algorithm can detect and extract bright points automaticallyand efectively, furthermore, it can use to recognize similar bright structures inother atmospheric layers. The size distribution of bright points is highly correla-tion with their intensity variation, implying that the observational performanceat photospheric-band of NVST achieve its expectation aim. The correlation ofvelocity distribution and shape variation is related to the down-flow or up-flowof material in the magnetic flux tubes. It is useful for revealing the chromo-spheric and coronal heating problem which is caused by the Alfven waves excitedfrom the oscillation of bright points. In the third part, we apply several non-linear analysis approaches to compare the statistical properties of polar faculaeand sunspot activity. Our main aim is to explore the statistical similarities ofperiodic variation, phase asynchronous, spatial distribution, chaotic and fractalfeatures of solar activities at high-and low-latitudes. Analysis results show thatpolar faculae and sunspot activity are anti-phase, and the former lead the latterby5-6years in phase, but this behaviour in diferent solar cycle and in diferenthemispheres difers from each other. Both of them exhibit north-south asyn-chrony and hemispheric asymmetry, however, they show diferent characteristicin a certain solar cycle and in a certain latitudinal band. Both of them show asimilar low-dimensional chaos, but the fractal dimension and long-range correla-tion show a slightly diference. All of the above results imply that the diference oftheir magnetic nature may be a major reason why they exhibit similar behavioursometimes and exhibit diferent property at other times.As mentioned above, studies on small-scale magnetic structures are very im- portant for understanding several unrevealed aspects in solar physics, thus it isstill necessary to continuing study their observational characteristics and phys-ical mechanism during a long time of future. For these two solar photosphericphenomena with strong magnetic feld strength, we will pay enough attentionto their magnetic complexity, self-similarity, oscillation behaviour, material flowsand periodic evolution properties. Furthermore, the poleward migration rate ofhigh-latitude phenomenon, cross-comparison of bright points with polar faculae,similarities and diferences of oscillation behaviour of them will be also investi-gated and discussed in the future. We believe that these studies will be deeperand clearer to develop and constraint the global or local dynamo theory, to un-derstand the upper atmospheric heating, and to realize the origin of fast solarwind, and so on.