Yukio Kozuka

Plasma Corona and Dust Corona of the Sun

Concerning the structure of the heliomagnetosphere, the 4—sector model with four vertical sector boundaries was proposed by Wilcox et al.(1965). In contrast to this model, the current sheet model(Shulz, 1973), or the two-hemisphere model(Saito, 1975) with the one warped horizontal neutral sheet were proposed (see the review by Saito et al., 198 9a).

Plasma Tail and Dust Tail of Comets

Generally, a comet has two tails; the blue plasma tail and the red dust tail (or Type 1 (ion) tail and Type 2 (dust) tail). The plasma tail is caused by an interaction between the solar wind and the cometary plasma, while the dust tail is by the solar radiation pressure to the cometary dust. The first purpose of the present paper is to review our works putting a focus mainly on Japanese products on the plasma tail disturbances in five outstanding comets which appeared after the comet Halley in 1986. The second purpose is to discuss on the field of the dusty plasma, that is not well understood.

Yohkoh Observations and Interplanetary Disturbances

Interplanetary disturbances during the five-year Yohkoh era are reviewed. Coronal holes have been observed by Yohkoh as source of recurrent disturbances. They have changed their size and latitudinal distribution according to decrease of solar activity. Large-scale coronal disturbances (LCDs) have been observed in association with coronal mass ejections, or source of non-recurrent disturbances.

Solar Cycle Variation of the Rotation of the Large-Scale Magnetic Field of the Sun

Large-scale structures of the solar magnetic field tend to rotate more rigidly than smaller-scale structure. It is known that coronal holes rotate quasi-rigidly while sunspots show a differential rotation. The rotational characteristics of some solar structures have been examined using autocorrelation techniques. Large-scale magnetic field, however, has not been discussed in detail. In the present study, we investigate the rotational characteristics of the large-scale solar magnetic field during about two solar activity cycles. A spherical-harmonic analysis is used for analyzing a distribution of the photospheric magnetic field.

Triple-Dipole Model on the Large-Scale Magnetic Structure of the Sun

It is necessary from a viewpoint of solar-terrestrial physics to study complex heliomagnetospheric structure and its solar cycle variation. The purpose of the present paper is to investigate large-scale structure of the solar magnetic fields, especially in relation to high-latitude prominences.

SOLAR CYCLE VARIATION OF LOCAL TIME DEPENDENCE IN FREQUENCY OF OCCURRENCE OF Pi2

Geomagnetic Pi2 pulsations are observed simultaneously with the onset of magnetic substorms. Individual Pi2 pulsations generally have a one—to—one correspondence with individual substorms (Saito, 1969). Therefore, the frequency of occurrence of the individual substorm can be estimated from the frequency of occurrence of the individual Pi2. In order to find some solar cycle variations in the frequency of occurrence of Pi2, Saito and Matsushita (1968) analyzed the data of Pi2 pulsations observed at Onagawa from 1956 to 1964. Together with the report by Afanasieva (1961), they pointed out that the local time of the maximum frequency of occurrence of Pi2 shows some solar cycle variation so that it tends to have a peak in pre—midnight hours during declining and minimum phases, and around midnight during maximum phases. Their analyses were limited in the data for two solar cycles. The purpose of the present paper is to examine the validity of their conclusion for solar cycle Nos. 20, 21 and the former half of 22.