Search

With the advent and successful operation of the 1.6 m aperture New Solar Telescope of Big Bear Solar Observatory (BBSO/NST), solar observation has entered the era of high resolution better than 0.1”. This permits us to carry out the case studies of single coronal heating events, to provide the original high-resolution observational evidence for finally solving the problem of coronal heating. By combining the high-resolution Helium I 10830 Å, TiO 7057 Å, and H a blue-wing (-0.7 Å) imaging data from the NST with the imaging data of extreme ultraviolet and longitudinal magnetic field observed simultaneously by the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board of the Solar Dynamics Observatory (SDO), we have analyzed the evolution of magnetic field in two tiny dynamical events of coronal heating (brightening of magnetic loops) that originate from the solar intergranular lanes. It is found that the footpoints of both brightening magnetic loops were all located in the one side of nearby neutral line of magnetic fields, the footpoints of one magnetic loop were accompanied by the disappearance of a small longitudinal magnetic element and the newly formed connection between two granulations, while the footpoints of another magnetic loop were accompanied by a weak variation of longitudinal magnetic field and the breakdown of a granulation. The observed result tends to suggest that the low-temperature and high-temperature outflows were produced simultaneously by the magnetic reconnection occurred among the solar granulations in the low-layer atmosphere. Meanwhile, it is noted that the high-resolution and high-accuracy polarization measurement of photospheric magnetic field is crucial for finally solving the problem of coronal heating. [ABSTRACT FROM AUTHOR]

Abstract: On July 22, 2011 and in the active region NOAA 11259 there ap- peared the event of the ejection of solar atmospheric Hα surges. According to the full-disc Hα observations of the Big Bear Solar Observatory in United States, three consecutive surges at one and the same place in the north of the main spot of the active region were discovered. The trajectories of these three surges exhib- ited the figure of straight lines, and their integral configuration is like an inverted Eiffel Tower. The first two surges are quite similar, and in each of them there appeared two bright points in the northern part of the main spot. After several minutes, the surges appeared in the midst of bright points. When the bright- ness of the bright points attained the maximum value, the surges spouted out from the midst of bright points. And after reaching the maximum altitude, they quickly vanished. Before the ejection of the third surge took place, no bright points appeared. Besides, its maximal altitude is merely one half of that of the first two surges. Via a comparison with the SDO/HMI (Solar Dynamics Obser- vatory/Helioseismic and Magnetic Imager) data of radial magnetic fields, it is found that in more than one hour before the appearance of the first surge there emerged bipolar magnetic fields in the region of ejection. Besides, in several min- utes before the ejection of each Hα surge the magnetic fluxes of positive polarity diminished. Via our analysis it is found that there appeared reconnections be- tween the newly emerging satellite magnetic fields and the preexisting magnetic fields in the spot, and this caused the continuous ejections of Hα surges. [Copyright &y& Elsevier]

With Solar Orbiter (SO) being put into successful operational observation, solar magnetic observation has entered the era of remote sensing from dual view points. In this paper, we carried out a simulation of correcting the 180 ∘ ambiguity of transverse magnetic field with magnetograms from dual view points using an analytical formula as well as the observations made by the Helioseismic and Magnetic Imager (HMI). Magnetograms of a small mature sunspot at different times were used to simulate magnetograms from dual view points. We find that in order to correct the 180 ∘ ambiguity of the vector magnetograms, it is sufficient to have a line-of-sight magnetogram from another view point to help to judge the direction of the transverse magnetic field. For the measuring accuracy of HMI, we estimate that a ∼ 30 ∘ angle formed from two observational points is the smallest angle to correct the 180 ∘ ambiguity around the place with the magnetic field strength of < 50 Gs. Correction for weaker magnetic fields surely needs larger separation angles, but considering projection effect, we propose that separation angles of ∼ 30 ∘ are the optimal angles for future space missions with the scientific aim of correcting the 180 ∘ ambiguity of vector magnetograms. [ABSTRACT FROM AUTHOR]

Abstract: In order to observe the bombardment of the solar chromosphere by high-speed electrons from flares, the fine-structure heliograph at Gan-Yu station of Purple Mountain Observatory has been upgraded to a high-speed CCD instrument that takes Hα filtergrams of solar local active regions. A focal reducer is added to the original optical system, and after introducing the polarization interference filter, the Hα filtergrams at different wavebands can be obtained by the fast CCD terminal. After repeated tests and improvements during the years 1999–2004, the upgrading is now completed with good result: the spatial resolution reaches 1 arcsec, and the temporal resolution is 30–40 frames per second. In November 2004, a class-M1.1 flare was observed. Comparing the blue-shifted Hα (Hα–0.5 Å) high-speed heliograms with the hard X-ray and microwave burst observations, we find that a pair of bright points moved toward each other during the rising phase of the initial flare. The converging motion was also displayed by the sources of the microwave burst. This phenomenon has never been observed before, and it can be explained as a shearing motion of the footpoints of the magnetic arch along the magnetic neutral line. [Copyright &y& Elsevier]

Seven mediated and small ejective events on the sun observed at Ganyu Observing Station of Purple Mountain Observatory in 2000 are investigated. It is found that they were not accompanied by brightening. Their lengths were in the range 1–2.5×104 km, their widths, 3–5×103 km, and their lifetimes, 3–7 minutes. They were produced at places of weak magnetic fields and far away from large sunspots. These ejections are interpreted by numerical simulation with 1-D hydrodynamic equations of flow along magnetic arcs. As demonstrated by the results, they are different from the spicules and surges simulated by Suematsu et al. and Shibata et al. They are not matter with photospheric or chromospheric densities pushed by shock waves or rebound shock waves toward the solar corona, rather, they are ejections formed by continuous matter flows after magnetic reconnection. After evolving for about 5 minutes, they can attain a stationary hydrodynamic state. [Copyright &y& Elsevier]

On September 14–18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance IIIb with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare. [Copyright &y& Elsevier]

On June 18, 2000, a small ejection phenomenon at the western limb of the sun was observed by Ganyu Station of Purple Mountain Observatory. Its lifetime was merely 15 minutes, and it did not belong to the ejection phenomena in late stages of solar flares. A very fine helical structure was visible. Assuming a velocity of 100 km/s produced by magnetic reconnection in the lower atmosphere and ignoring the Lorentz force, the height attainable by a column of ejecta of quasi-uniform density is derived, and the result is consistent with the observations. [Copyright &y& Elsevier]

This paper is to introduce a proposed deep space mission, which aims to perform in situ detection of the central structure, namely the magnetic reconnection current sheet, which drives the large-scale eruption on a star. The main focus of this mission is on the fine physical characteristics of the large-scale magnetic reconnection taking place on the Sun, our nearest star, revealing the secret of the most violent energy release process, also known as the solar storm, in the solar system. The scientific goal of this mission, magnetic reconnection, is a kernel process of energy conversion occurring in the magnetized plasma in the universe, and has long been a fairly important research topic or even research area in solar physics, space science, plasma physics, and the related fields. The in situ detection with a 5 ∼ 20 times enhanced spatial resolution of the instruments used on the Earth will provide us with the extra-clear images of the Sun and the related information. We are thus able to study, to learn, and to understand the Sun on an unprecedented platform, and further resolve the longstanding puzzle in the solar community regarding the fine physical property of the kernel process driving the solar eruption, as well as that of the coronal heating. [ABSTRACT FROM AUTHOR]