• Journal of Astronomy and Space Sciences
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• 제29권3호
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• pp.245-251
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• 2012

Since the development of surface magnetic features should reflect the evolution of the solar magnetic field in the deep interior of the Sun, it is crucial to study properties of sunspots and sunspot groups to understand the physical processes working below the solar surface. Here, using the data set of sunspot groups observed at the ButterStar observatory for 3,364 days from 2002 October 16 to 2011 December 31, we investigate temporal change of sunspot groups depending on their Z$\ddot{u}$rich classification type. Our main findings are as follows: (1) There are more sunspot groups in the southern hemisphere in solar cycle 23, while more sunspot groups appear in the northern hemisphere in solar cycle 24. We also note that in the declining phase of solar cycle 23 the decreasing tendency is apparently steeper in the solar northern hemisphere than in the solar southern hemisphere. (2) Some of sunspot group types make a secondary peak in the distribution between the solar maximum and the solar minimum. More importantly, in this particular data set, sunspot groups which have appeared in the solar southern hemisphere make a secondary peak 1 year after a secondary peak occurs in the solar northern hemisphere. (3) The temporal variations of small and large sunspot group numbers are disparate. That is, the number of large sunspot group declines earlier and faster and that the number of small sunspot group begins to rise earlier and faster. (4) The total number of observed sunspot is found to behave more likewise as the small sunspot group does. Hence, according to our findings, behaviors and evolution of small magnetic flux tubes and large magnetic flux tubes seem to be different over solar cycles. Finally, we conclude by briefly pointing out its implication on the space weather forecast.

• 천문학회보
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• 제36권1호
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• pp.40.2-40.2
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• 2011

We investigated solar flare occurrence probability depending on sunspot group classification and its area change. For this study, we used the McIntosh sunspot group classification and then selected most flare-productive six sunspot groups : DKI, DKC, EKI, EKC, FKI and FKC. For each group, we classified it into three sub-groups according to the sunspot group area change : increase, steady and decrease. For sunspot data, we used the NOAA's active region information for 19 years (from 1992.01 to 2010.12). As a result, we found that the probabilities of the all "increase" sub-groups is noticeably higher than those of other sub-groups. In case of FKC McIntosh sunspot group, for example, the M-class flare occurrence probability of the "increase" sub-group is 65% while the "decrease" and "steady" sub-groups are 50% and 44%, respectively. In summary, when sunspot group area increases, the probability of solar flares noticeably increases. This is statistical evidence that magnetic flux emergence is an very important mechanism for triggering solar flares.

• 천문학회보
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• 제36권2호
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• pp.98-98
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• 2011

We have investigated solar flare probability depending on sunspot classification, its area, and its area change using solar white light data. For this we used the McIntosh sunspot groups with most flare-productive regions : DKI, DKC, EKI, EKC, FKI and FKC. For each group, we classified it into three sub-groups according to sunspot area change : increase, steady, and decrease. For sunspot data, we used the NOAA active region information for 11 years (from January 2000 to December 2010): daily sunspot class and its area corrected for the projection effect. As a result, we find that the mean flare rates and the flare probabilities for the "increase" sub-groups are noticeably higher than those for other sub-groups. In case of the (M+X)-class flares of 'kc' groups, the mean flare rates of the "increase" sub-groups are more than two times than those of the "steady" sub-groups. This is statistical evidence that magnetic flux emergence is an very important for triggering solar flares since sunspot area increase can be a good proxy of magnetic flux emergence. In addition, we have examined the relationship between sunspot area and solar flare probability. For this, we classified each sunspot group into two sub-groups: large and small. In the case of compact group, the solar flare probabilities noticeably increase with its area.

• 천문학회보
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• 제43권2호
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• pp.45.3-46
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• 2018

Oscillations in a sunspot are easily detected through the Doppler velocity observation. Although the sunspot oscillations look erratic, the wavelet analysis show that they consist of successive wave packets which have strong power near three or five minutes. Previous studies found that 3-min oscillation at the chromosphere is a visual pattern of upward propagating acoustic waves along the magnetic field lines. Resent multi-height observations help this like vertical study, however, we also focus on horizontal facet to extend three dimensional understand of sunspot waves. So, we investigate a fragmented sunspot expected to have complex wave profiles according to the positions in the sunspot observed by the Fast Imaging Solar Spectrograph. We choose 4 points at different umbral cores as sampling positions to determine coherence of oscillations. The sets of cross-correlation with three and five minutes bandpass filters during a single wave packet reveal interesting results. Na I line show weak correlations with some lags, but Fe I and Ni I have strong correlations with no phase difference over the sunspots. It is more remarkable at Ni I line with 3-min bandpass that all sets of cross-correlation look like the autocorrelation. We can interpret this as sunspot oscillations occur spontaneously over a sunspot at photosphere but not at chromosphere. It implies a larger or deeper origin of 3-min sunspot oscillation.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.103-113
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• 2012

The ButterStar Observatory at the Dongducheon High School has been working for photographic observations of the Sun since October 16, 2002. In this study, we observed the Sun at the ButterStar observatory for 3,364 days from October 16, 2002 to December 31, 2011, and analyzed the photographic sunspot data obtained in 1,965 days. The correction factor $K_b$ for the entire observing period is 0.9519, which is calculated using the linear least square method to the relationship between the daily sunspot number, $R_B$, and the daily international relative sunspot number, $R_i$. The yearly correction factor calculated for each year varies slightly from year to year and shows a trend to change along the solar cycle. The correction factor is larger during the solar maxima and smaller during the solar minima in general. This implies that the discrepancy between a relative sunspot number, R, and the daily international relative sunspot number, $R_i$, can be reduced by using a yearly correction factor. From 2002 to 2008 in solar cycle 23, 35.4% and 64.6% of sunspot groups and 35.1% and 64.9% of isolated sunspots in average occurred in the northern hemisphere and in the southern hemisphere, respectively, and from 2008 to 2011 in solar cycle 24, 61.3% and 38.7% of sunspot groups and 65.0% and 35.0% of isolated sunspots were observed, respectively. This result shows that the occurrence frequency for each type of sunspot group changes along the solar cycle development, which can be interpreted as the emerging and decaying process of sunspot groups is different depending on the phase of solar cycle. Therefore, it is considered that a following study would contribute to the efforts to understand the dependence of the dynamo mechanism on the phase of solar cycle.

• 천문학회보
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• 제45권1호
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• pp.44.3-44.3
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• 2020

Sunspot substructure is an important subject to explain their stability and energy transport. Previous studies suggested two substructure models, monolithic and spaghetti model, but no clear evidence has been found supporting a particular model. To obtain the clue of the sunspot substructure the IRIS Mg II 2796Å slit-jaw images (SJI) were examined. The Mg II images formed in the chromosphere show bright patches inside umbrae which are regarded as an observational signature of upward propagating slow magnetohydrodynamic (MHD) waves. The slow MHD waves are expected to be generated by convective motion below the photosphere. By tracking the motion of the bright patches it is possible to estimate the locations of oscillation centers that correspond to the occurrence position of the convections. I investigated the spatial distribution of the oscillation center in a merging sunspot and found it is randomly distributed. It implies that the occurrence rate of the convective motion inside the sunspot is not much different from that of between the two sunspots, and supports the spaghetti model as the sunspot substructure.

• 천문학논총
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• 제15권1호
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• pp.21-29
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• 2000

We have analyzed 221 data of daily sunspot observations made during the period of January 1 to December 30 in 1999 and presented the daily relative sunspot numbers. During the year of 1999, our annual average of relative sunspot numbers is found to be 130.1. This number is obtained from the averaged daily number of 6.7 spot groups, in which there are about 45.9 distinct spots observed. According to the appearance of 384 spot groups, our analysis shows that the mean life time of spot group is about 5 day and 4.6 hours.

• 천문학논총
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• 제14권2호
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• pp.113-121
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• 1999

We have analyzed 251 data of the daily sunspot observations during the period of January 3 to December 31 in 1998 and present the daily relative sunspot numbers. During the 1998, the prehmmary annual average of the relative sunspot numbers is found to be 84.8 based on 26.6 distinct spots in a single group for 4.6 spot groups. According to the appearance of 286 spot groups, our analysis shows that the mean life time of spot group is about 4 day and 23.6 hours.

• 천문학논총
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• 제18권1호
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• pp.25-35
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• 2003

In this paper, we have re-examined the relative sunspot numbers from June 1987 to December 2002 observed at Korea Astronomy Observatory. For this we determined conversion factors (K) for each year data to derive the relative sunspot numbers. The estimated conversion factor ranges from 0.57 to 1.09 and has a trend to decrease with time, which seem to depend on the several effects such as observational system, observation methods, and experience of an observer. Our analysis shows that the newly-determined relative sunspot numbers are in much better agreements with the international sunspot numbers than the previously-determined ones in which the conversion factors were determined only four times. This result implies that we should determine the conversion factor for each year data. From these investigations, we also identified one and half solar cycles form our relative sunspot number.

• 천문학회보
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• 제37권1호
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• pp.88.2-88.2
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• 2012

We investigate solar flare occurrence rate and daily flare probability depending on McIntosh sunspot classification, its area, and its area change. For this we use the NOAA active region and GOES solar flare data for 15 years (from January 1996 to December 2010). We consider the most flare-productive 10 sunspot classification: 'Dko', 'Dai', 'Eai', 'Fai', 'Dki', 'Dkc', 'Eki', 'Ekc', 'Fki', and 'Fkc'. Sunspot area and its change can be a proxy of magnetic flux and its emergence/cancellation, respectively. we classify each sunspot group into two sub-groups: 'Large' and 'Small'. In addition, for each group, we classify it into three sub-groups according to sunspot group area change: 'Decrease', 'Steady', and 'Increase'. As a result, in the case of compact groups, their flare occurrence rates and daily flare probabilities noticeably increase with sunspot group area. We also find that the flare occurrence rates and daily flare probabilities for the 'Increase' sub-groups are noticeably higher than those for the other sub-groups. In case of the (M+X)-class flares of 'Dkc' group, the flare occurrence rate of the 'Increase' sub-group is three times higher than that of the 'Steady' sub-group. Mean flare occurrence rates and flare probabilities for all sunspot regions increase with the following order: 'Steady', 'Decrease', and 'Increase'. Our results statistically demonstrate that magnetic flux and its emergence enhance major solar flare occurrence. We are going to forecast solar flares based on these results and NOAA scale.