• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.76.1-76.1
• /
• 2014

We investigate the solar flare and CME occurrence rate and probability depending on sunspot class and its area change. These CMEs are front-side, partial and full halo CMEs associated with X-ray flares. For this we use the Solar Region Summary(SRS) from NOAA, NGDC flare catalog, and SOHO/LASCO CME catalog for 16 years (from January 1996 to December 2011). We classify each sunspot class into two sub-groups: "Large" and "Small". In addition, for each class, we classify it into three sub-groups according to sunspot class area change: "Decrease", "Steady", and "Increase". In terms of sunspot class area, the solar flare and CME occurrence probabilities noticeably increase at compact and large sunspot groups (e.g., 'Fkc'). In terms of sunspot area change, solar flare and CME occurrence probabilities for the "Increase" sub-groups are noticeably higher than those for the other sub-groups. For example, in case of the (M+X)-class flares of 'Dkc' class, the flare occurrence probability of the "Increase" sub-group is three times higher than that of the "Steady" sub-group. In case of the 'Eai' class, the CME occurrence probability of the "Increase" sub-groups is five time higher than that of the "Steady" sub-group. Our results demonstrate statistically that magnetic flux and its emergence enhance solar flare and CME occurrence, especially for compact and large sunspot groups.

• Journal of Astronomy and Space Sciences
• /
• v.23 no.3
• /
• pp.227-236
• /
• 2006

The fractal dimension is a quantitative parameter describing the characteristics of irregular time series. In this study, we use this parameter to analyze the irregular aspects of solar activity and to predict the maximum sunspot number in the following solar cycle by examining time series of the sunspot number. For this, we considered the daily sunspot number since 1850 from SIDC (Solar Influences Data analysis Center) and then estimated cycle variation of the fractal dimension by using Higuchi's method. We examined the relationship between this fractal dimension and the maximum monthly sunspot number in each solar cycle. As a result, we found that there is a strong inverse relationship between the fractal dimension and the maximum monthly sunspot number. By using this relation we predicted the maximum sunspot number in the solar cycle from the fractal dimension of the sunspot numbers during the solar activity increasing phase. The successful prediction is proven by a good correlation (r=0.89) between the observed and predicted maximum sunspot numbers in the solar cycles.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.123.2-123.2
• /
• 2012

We investigate the solar flare occurrence rate and daily flare probability in terms of the sunspot classification supplemented with sunspot area and its changes. For this we use the NOAA active region data and GOES solar flare data for 15 years (from January 1996 to December 2010). We consider the most flare-productive eleven sunspot classes in the McIntosh sunspot group classification. Sunspot area and its changes can be a proxy of magnetic flux and its emergence/cancellation, respectively. We classify each sunspot group into two sub-groups by its area: "Large" and "Small". In addition, for each group, we classify it into three sub-groups according to sunspot area changes: "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 in the 'Dkc' group, the flare occurrence rate of the "Increase" sub-group is three times higher than that of the "Steady" sub-group. Our results statistically demonstrate that magnetic flux and its emergence enhance the occurrence of major solar flares.

• Publications of The Korean Astronomical Society
• /
• v.12 no.1
• /
• pp.23-33
• /
• 1997

We have analyzed 223 data of the daily sunspot observations during the period of January 1 to December 31 in 1996 and present the daily relative sunspot numbers. During the 1996, the preliminary annual average of the relative sunspot numbers found to be 8.8 based on 3.7 distinct spots in a single group for 0.6 spot groups According to the appearance of 123 spot groups, our analysis shows that the mean life time of spot group is about 5 day and 5.8 hours. The proper conversion factor of the Korea Astronomy Observatory(KAO) derived from a comparison of one thousand one hundred and eighty observational sunspot numbers from 1992 to 1996 with those of international sunspot numbers is determined to be 1.17 instead of 0.97 which is in use.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.102.2-102.2
• /
• 2011

Sunspots usually appear in a group which can be classified by certain morphological criteria. In this study we examine the moments which are statistical parameters computed by summing over every pixels of contours, in order to quantify the morphological characteristics of a sunspot group. The moments can be additional characteristics to the sunspot group classification such as McIntosh classification. We are developing a program for image processing, detection of contours and computation of the moments using continuum images from SOHO/MDI. We apply the program to count the sunspot numbers from 303 continuum images in 2003. The sunspot numbers obtained by the program are compared with those by SIDC. The comparison shows that they have a good correlation (r=89%). We are extending this application to automatic sunspot classification (e.g., McIntosh classification) and flare forecasting.

• Journal of The Korean Astronomical Society
• /
• v.34 no.2
• /
• pp.119-127
• /
• 2001

We have analyzed 210 data of daily sunspot observations made during the period of January 3 to December 31 in 2000 and presented the daily relative sunspot numbers. For this work we estimated the conversion factors to derive the relative sunspot numbers: k=0.72 for the 20 cm refractor and k=0.56 for Solar Flare Telescope in KAO. During the year of 2000, our annual average of relative sunspot numbers is found to be 99.4. This number is obtained from the averaged daily number of 8.9 spot groups, in which there are about 62.5 distinct spots observed. According to the appearance of 423 spot groups, our analysis shows that the mean life time of the spot groups is about 4 day and 12.0 hours.

• Journal of Astronomy and Space Sciences
• /
• v.30 no.3
• /
• pp.163-168
• /
• 2013

Parameters associated with solar minimum have been studied to relate them to solar activity at solar maximum so that one could possibly predict behaviors of an upcoming solar cycle. The number of active days has been known as a reliable indicator of solar activity around solar minimum. Active days are days with sunspots reported on the solar disk. In this work, we have explored the relationship between the sunspot numbers at solar maximum and the characteristics of the monthly number of active days. Specifically, we have statistically examined how the maximum monthly sunspot number of a given solar cycle is correlated with the slope of the linear relationship between monthly sunspot numbers and the monthly number of active days for the corresponding solar cycle. We have calculated the linear correlation coefficient r and the Spearman rank-order correlation coefficient $r_s$ for data sets prepared under various conditions. Even though marginal correlations are found, they turn out to be insufficiently significant (r ~ 0.3). Nonetheless, we have confirmed that the slope of the linear relationship between monthly sunspot numbers and the monthly number of active days is less steep when solar cycles belonging to the "Modern Maximum" are considered compared with rests of solar cycles. We conclude, therefore, that the slope of the linear relationship between monthly sunspot numbers and the monthly number of active days is indeed dependent on the solar activity at its maxima, but that this simple relationship should be insufficient as a valid method to predict the following solar activity amplitude.

• Publications of The Korean Astronomical Society
• /
• v.13 no.1 s.14
• /
• pp.181-208
• /
• 1998

We have analyzed the sunspot and aurora data recorded in Go-Ryer-Sa. We have collected 35 records of sunspot observations for 46 days, and 232 records of auroral observations. To objectively estimate the periods of the solar activity appearing in these records a method of calculating the one-dimensional power spectrum from inhomogeneous data is developed, and applied to the sunspot and auroral data. We have found statistically significant 10.5 and 10 year periodicities in the distributions of sunspot and aurora records, respectively. These periods are consistent with the well-known solar activity cycle. There are indications of the long-term variations, but the period is not certain. We have also calculated the cross-correlations between the sunspot and auroral data. In particular, we have divided the aurora data into several subgroups to study their nature. We conclude that the historical records of strong auroral activity correspond to non-recurrent magnetic storms related to the sunspots. On the other hand, the records of weak auroral activity are thought to be related with the recurrent magnetic storms which occur frequently due to the coronal hole near the sunspot minimum.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.1
• /
• pp.23-29
• /
• 2021

Utilizing a new version of the sunspot number and group sunspot number dataset available since 2015, we have statistically studied the relationship between solar activity parameters describing solar cycles and the slope of the linear relationship between the monthly sunspot numbers and the monthly number of active days in percentage (AD). As an effort of evaluating possibilities in use of the number of active days to predict solar activity, it is worthwhile to revisit and extend the analysis performed earlier. In calculating the Pearson's linear correlation coefficient r, the Spearman's rank-order correlation coefficient rs, and the Kendall's τ coefficient with the rejection probability, we have calculated the slope for a given solar cycle in three different ways, namely, by counting the spotless day that occurred during the ascending phase and the descending phase of the solar cycle separately, and during the period corresponding to solar minimum ± 2 years as well. We have found that the maximum solar sunspot number of a given solar cycle and the duration of the ascending phase are hardly correlated with the slope of a linear function of the monthly sunspot numbers and AD. On the other hand, the duration of a solar cycle is found to be marginally correlated with the slope with the rejection probabilities less than a couple of percent. We have also attempted to compare the relation of the monthly sunspot numbers with AD for the even and odd solar cycles. It is inconclusive, however, that the slopes of the linear relationship between the monthly group numbers and AD are subject to the even and odd solar cycles.

• Publications of The Korean Astronomical Society
• /
• v.10 no.1
• /
• pp.57-66
• /
• 1995

We analyze 271 data of the daily sunspot observations during the period of January 1 to December 31 in 1994 and present the daily relative sunspot numbers. During the 1994, the preliminary annual average of the relative sunspot numbers is found to be 32.9 based on 12.4 distinct spots in a single group for 2.2 spot groups. According to the appearance of 146 spot groups, our analysis shows that the mean life time of spot group is about 4 day and 19.2 hours.