1:45 PM - 3:15 PM
[O11-P85] Search for Sunspot Groups Capable of Producing Major Solar Flares
Keywords:Sun, flares, Sunspot groups, Solar active region, Solar magnetic fields
1. Purpose
If we can accurately predict solar activity, we can reduce telecommunication disruptions and other impacts on society. Therefore, we focused on sunspot groups that appear on the photosphere in order to predict the timing of solar activity more accurately based on historical data. With regard to sunspot groups, Joy's law states that the leading pole is biased toward the equator due to the Coriolis effect. There is, however, large statistical variance in the distribution of sunspot groups. In this study, we aimed to find observables that could more clearly narrow down sunspot groups capable of producing large-scale flares.
2. Methods
A total of 250 sunspot groups for which magnetic field images were available were extracted from sketches of white light sunspots on the solar surface made by students at Musashi High School and Junior High School using 10cm telescopes from January 2008 to October 2017, the 24th solar cycle.
The axial tilt angle due to the Coriolis effect was measured using the magnetic field image[1] as a landmark. The average axis tilt angle at each sunspot group was calculated excluding the observations at the eastern and western ends of the solar image, where the errors in determining the axis tilt angle are large (Fig 1).
Next, we examined the axial tilt angle according to the major types in the Mount Wilson and McIntosh classification parameters of sunspot groups (Figs 2). It should be noted that those with a c parameter include δ-type sunspot groups.
3. Results
From Figure 1, Joy's law can be confirmed, and its regression line is almost consistent with that of a study conducted by D’Silva and Choudhuri.
Figure 2a - 2d shows that, with the exception of small monopole sunspot groups, axis tilt angles tend to follow two regression lines for each type, indicating strong correlations on large scales for each sunspot group type.
4. Discussion
4-1 Regarding Joy's Law
The results obtained from Figure 1 indicate that the intensity of the solar magnetic field is constant even on long-term scales and that there are no significant errors in the measurement method.
4-2 Regarding the east-west spread
Regarding the results in Figures 2a-2d, we thought that this might not be due to the size of the sunspot group. In order to discuss the intrinsic differences in each group, the slope of the regression line in Figure 1 was calculated by subtracting the increase in slope with latitude from the slope of the regression line. The relationship between the corrected axis tilt angle and the sunspot group size measured from the sketch was plotted (Fig 3a), but no significant correlation was identified.
Then, excluding unipolar groups with large empirical variability and groups with few data points, we found that most sunspot groups follow two regression lines within an error range of 5 to 15 degrees in the east-west direction (Fig 3b). Here, we can suggest that sunspot group size may be positively correlated with tilt angle on the 5-15 degree spread scale.
For small groups, it is thought that the variation is caused by the mechanism at the top of the group. For groups with a large size scale, there were many groups where the tilt angle tended to be relatively small (Fig 3b, red).
4-3 Sunspot groups capable of major flares
In order to further discuss these issues based on the three dimensional extent, we referred to the image of the upper part of the chromosphere by Hα absorption lines[1]. Large-scale groups with small axial tilt angles (Fig 3b, red) are considered to have magnetic flux tubes lying three-dimensionally and thinly near the photosphere, while large-scale groups with small axial tilt angles are considered to extend upward and higher due to magnetic buoyancy.
Sunspot groups with large axial tilt angles relative to the photosphere (Fig 3b, orange) have dense magnetic flux tubes and, like δ-type sunspot groups, have a high probability of producing large-scale flares.
5. Conclusion
Based on the sunspot sketches at our school, we were able to confirm Joy's law and deepen the discussion on the dispersion of axial tilt angles. As a consequence, it was clarified that the tilt angle can be a new method for selecting sunspot groups capable of producing large-scale flares.
In the future, we would like to examine the difference between the two types of formation represented by the two regression lines in Figures 2,3 in more detail, and to examine the connection with the chromosphere more carefully, so that we can present more coherent data.
Reference
[1]Kawaguchi City Science Museum Solar Images.
If we can accurately predict solar activity, we can reduce telecommunication disruptions and other impacts on society. Therefore, we focused on sunspot groups that appear on the photosphere in order to predict the timing of solar activity more accurately based on historical data. With regard to sunspot groups, Joy's law states that the leading pole is biased toward the equator due to the Coriolis effect. There is, however, large statistical variance in the distribution of sunspot groups. In this study, we aimed to find observables that could more clearly narrow down sunspot groups capable of producing large-scale flares.
2. Methods
A total of 250 sunspot groups for which magnetic field images were available were extracted from sketches of white light sunspots on the solar surface made by students at Musashi High School and Junior High School using 10cm telescopes from January 2008 to October 2017, the 24th solar cycle.
The axial tilt angle due to the Coriolis effect was measured using the magnetic field image[1] as a landmark. The average axis tilt angle at each sunspot group was calculated excluding the observations at the eastern and western ends of the solar image, where the errors in determining the axis tilt angle are large (Fig 1).
Next, we examined the axial tilt angle according to the major types in the Mount Wilson and McIntosh classification parameters of sunspot groups (Figs 2). It should be noted that those with a c parameter include δ-type sunspot groups.
3. Results
From Figure 1, Joy's law can be confirmed, and its regression line is almost consistent with that of a study conducted by D’Silva and Choudhuri.
Figure 2a - 2d shows that, with the exception of small monopole sunspot groups, axis tilt angles tend to follow two regression lines for each type, indicating strong correlations on large scales for each sunspot group type.
4. Discussion
4-1 Regarding Joy's Law
The results obtained from Figure 1 indicate that the intensity of the solar magnetic field is constant even on long-term scales and that there are no significant errors in the measurement method.
4-2 Regarding the east-west spread
Regarding the results in Figures 2a-2d, we thought that this might not be due to the size of the sunspot group. In order to discuss the intrinsic differences in each group, the slope of the regression line in Figure 1 was calculated by subtracting the increase in slope with latitude from the slope of the regression line. The relationship between the corrected axis tilt angle and the sunspot group size measured from the sketch was plotted (Fig 3a), but no significant correlation was identified.
Then, excluding unipolar groups with large empirical variability and groups with few data points, we found that most sunspot groups follow two regression lines within an error range of 5 to 15 degrees in the east-west direction (Fig 3b). Here, we can suggest that sunspot group size may be positively correlated with tilt angle on the 5-15 degree spread scale.
For small groups, it is thought that the variation is caused by the mechanism at the top of the group. For groups with a large size scale, there were many groups where the tilt angle tended to be relatively small (Fig 3b, red).
4-3 Sunspot groups capable of major flares
In order to further discuss these issues based on the three dimensional extent, we referred to the image of the upper part of the chromosphere by Hα absorption lines[1]. Large-scale groups with small axial tilt angles (Fig 3b, red) are considered to have magnetic flux tubes lying three-dimensionally and thinly near the photosphere, while large-scale groups with small axial tilt angles are considered to extend upward and higher due to magnetic buoyancy.
Sunspot groups with large axial tilt angles relative to the photosphere (Fig 3b, orange) have dense magnetic flux tubes and, like δ-type sunspot groups, have a high probability of producing large-scale flares.
5. Conclusion
Based on the sunspot sketches at our school, we were able to confirm Joy's law and deepen the discussion on the dispersion of axial tilt angles. As a consequence, it was clarified that the tilt angle can be a new method for selecting sunspot groups capable of producing large-scale flares.
In the future, we would like to examine the difference between the two types of formation represented by the two regression lines in Figures 2,3 in more detail, and to examine the connection with the chromosphere more carefully, so that we can present more coherent data.
Reference
[1]Kawaguchi City Science Museum Solar Images.