Ichiro Kawaguchi

Morphological and evolutional features of Ellerman bombs

Morphological and evolutional features of Ellerman bombs were studied with Hα filtergrams of two active regions very close to the solar limb. We quantitatively determined the elongated or spike-like shape of the bomb. The mean apparent length of 174 bombs is 1.1 arc sec, while 80% of 204 bombs have a diameter of less than 0.6 arc sec. The mean lifetime of 77 bombs is about 12 min at Hα - 1.2 Å. The first maximum brightness of a typical bomb is attained, on average in about 2 min. Bombs grow longer in the first brightening phase and their mean upward velocity explains the blue asymmetry of Hα emission profiles of moustaches.

Morphological study of the solar granulation

A time sequence of granulation images of 46 min long has allowed us to make a detailed study of the evolution of granules in an area of approximately 17″ × 17″ on the solar surface. It is found that the granules evolve by repeated fragmentation into smaller granules or merging with adjacent ones and that there are few granules which appear in the intergranular lanes as new granules (Table III). The statistical nature of granules is as follows:(1)A family of granules is defined as a group of granules produced from a single granule by fragmentation or merging. The lifetime is estimated for single granules and for families of granules. The lifetime shows a close correlation with the maximum size of a single granule or with that of the largest granule belonging to a family (Figures 5 and 7).(2)The smaller the size, the more probably a granule will disappear without further fragmentation or merging. The granule whose size is larger than 2″ will certainly split or merge as the next evolutional step (Table IV).

THE VELOCITY FIELD ASSOCIATED WITH THE BIRTH OF SUNSPOTS

A velocity field is found to occur prior to the birth of sunspots or during the rapidly developing phase of new spots. Fraunhofer lines are always shifted redwards in the observed active regions which are situated at various distances from the disk center. The velocity amplitude derived from Na i D1-line, λ 5895.940, amounts to, at maximum, 1.5 km s−1 which is always a little larger than that derived from the weaker line, NI i λ 5892.883. The velocity field disappears when the spot ceases to grow. The lifetime of the velocity is, at least, 1 hr. The velocity field is interpreted in terms of the continuous downward flow in the process of formation of sunspots.Bray and Loughhead (1964) regard the disturbance in the granulation pattern accompanying the birth and growth of sunspot pores as an evidence of the existence of rising loops of magnetic flux. In view of the similarity of the phase of development of active regions and the lifetime in the observations by Bray and Loughhead and by us, we suggest that the velocity field may be a spectroscopic feature accompanying the rising magnetic loops in the photosphere and the chromosphere. We briefly discuss the observed mode of penetration of the magnetic flux to the solar surface before and after the appearance of AFSs.

The brightening of sunspot umbra observed on 29 October, 1972

Brief descriptions are given of the spectroscopic and the monochromatic observations of the umbral brightening on 29 October, 1972. The source of the brightening is attributed to the kinetic energy of the infalling coronal matter with a final velocity of 200 km s−1, into the umbral gas. The spectra of this brightening reveal many hydrogen and metallic emission lines. The variety of the widths of these lines indicates the existence of complex nonthermal velocity field and of the stratification of various emitting conditions in the umbral brightening. The kinetic energy of the falling matter would be expended not only for producing the emissions, but also for exciting the complex velocity field of nonthermal motion.

On the dome formation in the corona around a prominence observed at the total eclipse of 15 February 1961

A conspicuous coronal dome formation around a prominence was photographed during the eclipse of 15 February 1961 with the 120-cm reflector of the Haute Provence Observatory with an excellent image definition. A detailed isophotic map of the dome formation was constructed after estimating a calibration curve. The bright dome is interpreted as an aggregate of free electrons trapped in a gigantic bundle of magnetic lines of force. The free electrons are concentrated in the central part and the degree of concentration seems to be the least at the top of dome and to increase with decreasing height. The bright dome surrounds a dark one. The minimum extension of the dark dome formation along the line of sight is estimated. It seems that the density of coronal matter is much reduced around the prominence compared with the overall coronal density.

Brightening phenomena in prominences at the center of the Hα line

Two examples of sudden brightenings in local regions of active prominences as observed at the center of the Hα line are described. The origin of the brightenings is discussed in terms of Doppler shifts along the line of sight, Doppler brightenings and intrinsic changes of physical conditions. It is shown that the two examples presented here have common characteristics and the origin may probably be attributed to intrinsic changes of physical conditions.

Progressive brightenings observed in the wing of Hα line

In an active region, several points were observed to brighten progressively on the monochromatic image of Hα - 1.2 Å formed by the Domeless Solar Telescope installed recently at Hida Observatory. The phenomena were interpreted as small flares or subflares. The propagation velocity was measured in two cases and discussed in terms of the multiple loop activation observed in EUV radiation.

A small-scale energy release observed on the limb

The D3 emission lines observed on the emerging flux loops and mound prominences above the limb were locally found to consist of two components, i.e., the main and the broadened components. A number of Doppler shifted emission lines, separated distinctly from the main body of the emission lines were also detected, which we call the separated components. On the sequential spectrograms, the lifetimes of these broadened and separated components were obtained and their histograms were made.We present the results of fitting the observed emission lines with the sum of two gaussian profiles in two simple cases under two different assumptions. In each assumption, it is found that the line-of-sight velocities of the broadened components with lifetimes shorter than 10 min monotonously increase with time and we attribute this behaviour to a single ejection of mass from the parent structures. In the broadened components with lifetimes longer than 10 min, the acceleration turns on and off alternately, each with a duration of several minutes. We attribute this behaviour to multiple ejections of mass.Finally, it is shown that the corona over the active region is supplied with enough mass for the formation of a coronal condensation if the ejected mass diffuses out high into the corona and some heating mechanisms for the mass switch on.

Photospheric velocity field associated with moustaches

The photospheric velocity field was observed in an active region which was prolific in moustaches. It is shown that the moustaches occur at the locations where the sign of the line-of-sight velocity changes, and that the extension of the velocity field is large (≈104 km) compared with the dimension of moustaches.

Coronal prominences on the disk observed on 29 October 1972

A group of coronal prominences appeared over a large sunspot group near the central meridian on October 29, 1972. The bright points, which were most clearly seen on the Hα-image taken at the line center, are interpreted as the points of inflow of the prominence matter into the penumbra. The amount of mass transported by the largest prominence among the group is found to share a considerable fraction of the total mass which may be contained in the permanent coronal condensation over the spot group. The observational data for the microwave emission from the spot group is discussed in relation to this phenomenon.