The Study of Solar Intranetwork Magnetic Fields

This thesis consists of two parts.Part Ⅰis a review of small-scale activity phenomena in solar atmosphere.These phenomena are:(1)jets,including spicules.macrospicules,Hα jets,EUV jets,and X-ray jets;(b)bright (dark) point features,such as network bright points,X-ray bright points,microwave bright points,magnetic bright points,and He I 10830 Å dark points;(c)explosive phenomena(e.g.,transition region explosive events,mini-filament eruption);(d)transient brightenings and EUV blinkers;(e)MHD turbulent events;(f)microflares and nanoflares.The properties of these active phenomena are carefully described and the theoretical interpretations are also presented. Part Ⅱ is a series papers on the properties of intranetwork(IN)magnetic elements using the best magnetograms on quiet-Sun ever obtained by Big Bear Solar Observatory (BBSO) and Huairou Solar Observation Station (HSOS).Most of the results presented in this dissertation are new findings obtained mainly by the author. In Paper 1,we present the lifetime of IN elements for the first time.The lifetime ranges from 0.2 hour to 7.5 hour,with a mean lifetime of 2.1 hour.Paper 2 describes the velocity fields of IN elements.By tracing individual elements,we have measured horizontal velocity and studied motion patterns of Intranetwork(IN) magnetic elements for the first time.The magnetograms obtained at Big Bear Solar Observatory span an interval of 10-hour and cover an area of 310×240 arc sec².In general,IN elements move radially and isotropically outwards from emergence centers to boundaries of supergranule cells at first.However,when they reach halfway between cell centers and boundaries,the motion of IN elements is non-isotropic,there are prior directions.Most of IN elements move towards the edges of network elements.There are two components of the velocity fields:radial velocity and circular velocity.From the centers to the boundaries of supergranule cells,the magnitude of the radial velocity decreases gradually;but that of the circular velocity increases obviously,at halfway between cell center and boundary,the circular acceleration reachs the maximum,about 10^-1 ms^-2.The mean circular velocity near the boundary is about 0.4km s^-1 .The horizontal speeds deduced by tracing 768 intranetwork elements range from0.05 km s^-1 to 0.8 km s^-1 with a peak distribution at 0.4 kms^-1 .Both within the supergranule cells and on the boundaries,there are convergence centers,but divergence centers always exist within supergranule cells.There seems to be a regular distribution of IN velocity fields on large-scale range of solar surface.This reseach is also the begining work.The regular distribution of velocity fields can be used to interpret the regular distribution of current helicity and magnetic field helicity on different aspects. The appear patterns and disappear patterns of IN elements are especially studied in Paper 3.The appearance of IN elements can be classified into the following categories:half of the total IN elements emerge as clusters of mixed polarities somewhere within the network cells,one fifth appear as ephemeral regions (tiny bipoles),one fifth result from the merging of several elements of a given polarity,and one tenth appear by fragmentation of larger elements.IN elements disappear in four ways:one third of total IN elements cancel with elements of opposite polarity,one third decay into weak fields without apparent interaction with other elements,one fourth merge with IN or network elements of the same polarity,and one tenth split into smaller IN elements below detecting limit.About one ninth (one sixth) of the IN elements merge (cancel) with network features,consequently,part of the flux in network features is built up from former IN magnetic flux,and part is eliminated by IN elements.The net effect of merging and cancellation is a gradual reduction of the total flux of network elements in the 10 hours observational interval.It seems that not all the network magnetic flux is the remnant of active region magnetic flux.In Paper 4,we have studied the polarity dist ribution of intranetwork and network fields. Using very deep magnetog rams obtained at Huairou Solar Observation Station (HSOS)and Big Bear Solar Observatory (BBSO), we are able to determine 100 network cells and measure the polarities of IN and network mag netic flux within each cell. The analy sis reveals that in enhance networks, about 90% of IN and network magnetic flux are opposi te polarity; in mixed-polarity network, 75% are opposite polarity. We point out firstly that IN fields and network fields are connected topologically, althouth they are much different on many aspects. In theory, we have studied the stability of small mag netic flux tube. One of the most important stability of plasma physics is interchange instability. On the study of small flux tube stability, we first consider the stabilizing effects of supergranular velocity fields, twists of magnetic field-lines, gas pressure and gas pressure gradient interior of flux tubes, and we have given the following results :on the solar conditions, velocity fields, twists of field-lines and internal gas pressure stabilize flux tubes.