Yoichiro Hanaoka

Rotating eruption of an untwisting filament triggered by the 3B flare of 25 April, 1984

A great 3B flare, whose X-ray class was X13, occurred over a delta-sunspot at 00: 01 UT on April 25, 1984. Before the flare, a strong magnetic shear was found to be formed along the neutral line in the delta-sunspot with shear motions of umbrae. The shear motions of the umbrae were caused by the successive emergence of a magnetic flux rope.Before the flare, several groups of sheared Hα threads and filaments were found to merge into an elongated filament along the neutral line through the delta-sunspot. In the merging process the helical twists were formed in the filament by the reconnection as in the Pneumans (1983) model.At the post-maximum phase of the flare, the helically twisted filament spouted out with an untwisting rotation. Examining the morphological and dynamical features of the filament eruption, we concluded that it has some typical features of the flare spray and that it seems to be accelerated by the sweeping-magnetictwist mechanism proposed by Shibata and Uchida (1986).

The post flare loops observed at the total eclipse of February 16, 1980

A post flare loop system was observed on the west limb at the total solar eclipse of February 16, 1980 in Kenya. Analyzing the monochromatic images and the flash spectra, we obtained the following results: (1) the lower part of the post flare loop system is characterized mainly by distinct cool loops of Hα and Fe x 6374. Fe x 6374 emitting plasma (Te = 1.0 × 106 K) is highly concentrated in the loops. The 6374 loops are broader in diameter and located very close to but a little higher than the corresponding Hα loops. The electron densities of the dense part in Hα and Fe x 6374 loops are 1011 cm-3 and 6 × 109cm-3, respectively; (2) the Ca xv emitting region (3.5 × 106 K) is confined to the upper part of the post flare loops. The electron density of this hot region is estimated as 8 × 109 cm-3 from the Ca xv line intensity ratio, I(λ5694)I(λ5445). These observational results led us to construct an empirical model of the post flare loop system which is consistent with the reconnection model of Kopp and Pneuman (1976).

Ion-sound model of microwave spikes with fast shocks in the reconnection region

A new model for solar spike bursts is considered based on the interaction of Langmuir waves with ion-sound waves: l+s→t. Such a mechanism can operate in shock fronts, propagating from a magnetic reconnection region. New observations of microwave millisecond spikes are discussed. They have been observed in two events: 4 November 1997 between 05:52–06:10xa0UT and 28 November 1997 between 05:00–05:10xa0UT using the multichannel spectrograph in the range 2.6–3.8xa0GHz of Beijing AO. Yohkoh/SXT images in the AR and SOHO EIT images testify to a reconstruction of bright loops after the escape of a CME. A fast shock front might be manifested as a very bright line in Te SXT maps (up to 20xa0MK) above dense structures in emission measure (EM) maps. Moreover one can see at the moment of spike emission (for the 28 November 1997 event) an additional maximum at the loop top on the HXR map in the AR as principal evidence of fast shock propagation. The model gives the ordinary mode of spike emission. Sometimes we observed a different polarization of microwave spikes that might be connected with the depolarization of the emission in the transverse magnetic field and rather in the vanishing magnetic field in the middle of the QT region. Duration and frequency band of isolated spikes are connected with parameters of fast particle beams and shock front. Millisecond microwave spikes are probably a unique manifestation of flare fast shocks in the radio emission.

On the Microwave Spike Emission of the September 6, 1992 Flare

The main aim of this paper is to estimate, from multispectral observations, the plasma parameters in a microwave burst source which was also the site of spike emission. This information is essential for the determination of the spike emission process. By analyzing one-dimensional source distributions observed with the SSRT at 5.7 GHz and correlating them with Yohkoh X-ray and Nobeyama 17 GHz images, we have concluded that the microwave emitting region was larger than the soft X-ray loop-top source, and that the origin of the burst could be explained by gyrosynchrotron emission of non-thermal electrons in a magnetic field of approximately 100 G. It has been shown that the source of 5.7 GHz spikes observed during the burst was located close to an SXR-emitting loop with high density and temperature and a relatively low magnetic field. Thus, plasma emission is the most favourable radiation mechanism for the generation of the sub-arc-second microwave pulses.

Mass motions in active region filaments

Mass motions in active region filaments of regions NOAA 4171 and McMath 16208 are analyzed. Both regions were continuously observed with the Zeiss Lyot filter for about a week at the Hida Observatory. As for NOAA 4171, Dopplergrams are made from the Hα filtergrams of 7 wavelengths for the qualitative study of the velocity fields in the filament, and Beckers cloud model analysis is employed for a quantitative study of them. Dopplergrams of McMath 16208 are also constructed for qualitative analyses to determine whether the results derived from the analysis of NOAA 4171 are applicable to this region.The following results are obtained. Matter in the long-lived filaments, which lie along the magnetic neutral lines, flows generally horizontally and along the axes of the filaments. Since the matter in the filaments is considered to flow along the magnetic field, the magnetic fields in the filaments must be highly sheared. The same patterns of mass flow are found in the same filaments on successive days; some of them last for at least several days. Some filaments show long-lived symmetrical downflows to both of their ends in which the velocity is about 30 km s-1. Such flows are seen both in NOAA 4171 and McMath 16208. We show a morphological model of such flows.

The innermost corona observed at the 1973 June 30 eclipse

Slitless flash spectrograms in heights below 8000 km above the solar limb were obtained by the University of Kyoto Expedition at Atar, Mauritania. The integrated intensities of Fexivλ5303, Fexλ6374, Fexiλ7892, and the continuum are measured as a function of height above the solar limb at eleven points (P.A. = 284–300°) around the third contact point. It is found that a significant amount of the emission in Fexλ6374 originates in chromospheric levels well below 8000 km. This implies that the interspicular region of the chromosphere is occupied by coronal material. The average values of the electron temperature and the electron density in the interspicular region are derived from the Fexλ6374 and the Fexiλ7892 intensities on the assumption of spherical symmetry: Te = 0.9–1.1 × 106 K and Ne = 9–10 × 108 cm−3. The intensity variations of the coronal lines and the continuum with position angle are also studied. Strong correlations between Fexivλ5303 and the continuum and between Fexλ6374 and Fexiλ7892 are found. From the Fexλ6374 intensities it is inferred that there is a density fluctuation in the innermost corona by at least a factor of two.

Emission curve of growth for Feii in chromospheric limb spectra

The 270 chromospheric emission lines of Feii ranging between 2000 and 3200 Å observed by Skylab at a height of 4″ (2900 km) above the limb of the quiet Sun are analyzed by the emission curve of growth method, using newly calculated gf-values. It is derived that the excitation temperature is 7.2 × 103 K and that the turbulent velocity is consistent with the previous results that the microturbulent velocity is lower than 10 km s−1 in the cool (<104 K) region of the chromosphere.