qs049.kozuka03 Posted: 31-Jan-93 Updated: 06-Nov-93, 7-Aug-94, 13-May-95, 03-Feb-96, 20-Sep-96 Events specified: N/A
Y. Kozuka, T. Watanabe, M. Ohyama, M. Kojima (STE Lab., Nagoya Univ.) T. Saito (Astrogeophys Inst., Tohoku Univ.)
Rotation of the coronal magnetic field is different from that of the photospheric field. It is known that the coronal field rotates quasi-rigidly, while the photospheric field shows a differential rotation. It is reported that the photospheric and coronal fields rotate differently in the northern and southern hemispheres. Such a north-south asymmetry is found also in the IMF polarity patterns for many solar cycles.
A detail study of the rotation of the coronal structures is useful not only for the study of the structures of the solar magnetic field but also for the studies of the heliospheric structure, a mechanism of recurrent geomagnetic storms, a periodicity of occurrence of flares, and so on.
We will investigate characteristics of the rotation of the large-scale coronal structures, and examine a relationship between the corona and characteristic structures in the interplanetary space. Synoptic charts of SXT images and magnetic field data will be used in the analysis.
Update 20-Sep-96
We have carried out a spherical harmonic analysis of the photospheric magnetic field over the recent two solar activity cycles. The previous results showed that the horizontal dipole (n=1, m=1) and quadrupole (n=2, m=2) components of the multipole expansion have their own rotation periods, and that the rotation periods exhibit a solar cycle dependence. In the present study, we investigated a geometrical relation between distributions of these large-scale components of the solar magnetic field and regions in which large solar flares occurred. Solar flares larger than importance 3 or X-class for cycle 22 were examined in the analysis. The result shows that the regions where the large flares occurred located near the magnetic neutral lines of both harmonic components. After the flare occurred, a field strength of each component decreased. These suggest that the distribution of the lower harmonic components of the solar magnetic field influences on the occurrence of the large solar flares.
Update 03-Feb-96
A relationship between the large-scale solar magnetic field and the interplanetary magnetic field (IMF) was investigated in detail. We examined a long-term variation of a recurrence period of the IMF polarity using a dynamic-autocorrelation method. The recurrence period of the IMF polarity clearly shows a solar cycle dependence. On the other hand, the rotation periods of the horizontal dipole and quadrupole components of the photospheric magnetic field also exhibit their own solar cycle dependences. We compared the recurrence period of the IMF polarity with the rotation period of these lower harmonic components. An amplitude of each component was also taken into account.
The dipole component is usually dominant through the analyzed period though the quadrupole sometimes excels it. When the quadrupole component is predominant, the IMF shows a four-sector pattern and the recurrence period corresponds to the rotation period of the quadrupole. The long-term variation of the recurrence period of the IMF polarity is controlled by both of the horizontal dipole and quadrupole components.
We will examine soft X-ray structures associating with the variation of the recurrence period of the IMF polarity.
Update 13-May-95
We investigated a influence of the large-scale solar structures on the interplanetary magnetic field (IMF). The IMF polarity shows a characteristic recurrence pattern during solar cycle. The recurrence period of the IMF polarity is usually about 27 days, while the period of about 28 to 29 days sometimes appears. We compared the recurrence pattern of the IMF polarity with the characteristics of the rotation of the large-scale solar magnetic field.
The IMF polarity shows a 28-day recurrence in the rising phase of both cycles and near the maximum of cycle 22. The recurrence pattern of the IMF polarity corresponds with the changes of the rotation periods of the horizontal dipole (n=1, m=1) and quadrupole (n=2, m=2) components of the multipole expansion. It is concluded that the rotations of these lower harmonic components of the solar magnetic field affect the variation of the recurrence period of the IMF.
The soft X-ray structure shows a rapid change when the IMF polarity pattern changes. A relationship between large-scale solar magnetic field structures and the soft X-ray corona should be investigated at the next stage.
Update 7-Aug-94
In order to investigate a relationship between a rotation of large-scale soft X-ray coronal structures and that of the magnetic field, we carried out a spherical harmonic analysis of the photospheric magnetic field data obtained by Kitt Peak magnetogram for sunspot cycle 22. Carrington longitudes of the horizontal magnetic axes were calculated from spherical harmonic coefficients. Rotation period of the solar magnetic field were obtained from the change of the Carrington longitudes of the axes.
The result of the analysis for the horizontal dipole (n=1, m=1) and quadrupole (n=2, m=2) components shows that each harmonic components have different rotation periods. This is correspond to the difference of the rotation periods due to the size of the soft X-ray coronal structures which we have already reported.
Update 06-Nov-93
We investigated characteristics of the rotation of the large-scale coronal structures by using synoptic charts of the soft X-ray corona. The synoptic charts during Carrington rotation 1851-1861 were used in this analysis. An autocorrelation technique was used in order to investigate rotation periods of the corona. Autocorrelation coefficients were calculated on every ten degrees in the latitude. The rotation period of each characteristic structures was also calculated by tracking changes in the longitude on the synoptic charts.
The autocorrelation coefficients in the higher latitude are larger than those in the lower latitude. This result indicates that the autocorrelation analysis was influenced on structures of the quiet corona in the high latitude region, while on active regions in the low latitude region. The result of the autocorrelation analysis also shows that the corona in the high latitude rotates quasi-rigidly. It is found by this analysis that the rotation periods in the northern hemisphere are different from those in the southern hemisphere. The rotation periods of active regions and quiet coronal structures in the low latitudinal range are about 27.3 and 26.9 days, respectively, in the northern hemisphere, while 26.8 and 27.2 days, respectively, in the southern hemisphere.