- Email: [email protected]
Distribution of CMEs with Different Angular Widths and Comparison with the Phase of Sunspot Number in the 23rd Solar Cycle
CHINESE ASTRONOMY AND ASTROPHYSICS
ELSEVIER
Chinese Astronomy and Astrophysics 38 (2014) 85–91
Distribution of CMEs with Different Angular Widths and Comparison with the Phase of Sunspot Number in the 23rd Solar Cycle † MENG Wei-juan1,2 LE Gui-ming1,2 LIN Zhao-xiang1 ZHANG Yong2,3 YANG Xing-xing2,3 1
2
South-Center University for Nationalities, Wuhan 430074 National Satellite Meteorology Center for Space Weather, China Meteorological Administration, Beijing 100081 3 Nanjing University of Information Science and Technology, Nanjing 210044
Abstract The variation of the number of coronal mass ejections (CMEs) with different angular widths in the period of 1996-2008 is analyzed statistically in this paper, together with a comparison of the feature of time variation between the number of CMEs with some typical angular widths and the number of sunspots. The analyzed result indicates that the number of CMEs with the angular widths of 0◦ ∼ 180◦ occupies an over 95% proportion in the total number of CMEs, the full-halo CMEs takes a proportion of 2.83%, and the number of CMEs with the angular widths of 301◦ ∼ 359◦ is very small. There are three peaks in the number distribution of CMEs with the angular widths of 0◦ ∼ 60◦ , which is not coincident with the feature of the time variation of sunspot number. There is no double-peaked number distribution for the CMEs with the angular widths of 121◦ ∼ 180◦. The number distribution of the full-halo CMEs has double peaks evidently, with the first peak value at 2001, and the second peak value at 2005, which is not synchronized with the variation of sunspot number. Key words: solar activities–coronal mass ejections (CMEs)—angular width— sunspot number
†
Supported by National Natural Science Foundation Received 2012–12–03; revised version 2013–02–17 A translation of Chin. J. Space Sci. Vol. 33, No. 3, pp. 225–230, 2013 [email protected]. Corresponding author: LE Gui-ming, [email protected]
0275-1062/14/$-see front matter 2014 Elsevier All rights reserved. c 2014B.V. 0275-1062/01/$-see front © matter Elsevier Science B. V. All rights reserved. doi:10.1016/j.chinastron.2014.01.008 PII:
86
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
1. INTRODUCTION The coronal mass ejection (CME) indicates such a phenomenon that a great amount of mass escaped from the solar corona, and entered into the interplanetary space, and it belongs to a kind of very violent solar activity. Some CMEs may produce coronal shocks when they are moving in the solar corona, which accelerate charged particles and result in the solar energetic particle events. After the CME entered into the interplanetary space, it becomes an interplanetary CME (ICME), when the ICME and its driving shock arrived in the magnetosphere, they may cause magnetic storm if the dynamic pressure and the southward magnetic field are strong enough, and thus to produce a disastrous space weather. A majority of large magnetic storms are caused by CMEs[1−3] , and the interplanetary sources of most large magnetic storms in the 23rd solar cycle are CMEs[4] . The large slow-varying solar energetic particle events are also correlated with ICMEs[5] , hence, CMEs are the main disturbing sources for the space weather, and therefore become a focal point in the research. Since the coronagraph LASCO with a large field of view on board of the SOHO satellite started to observe CMEs, a lot of observed data of CMEs have been obtained, including a series of information about the speed and angular width of CMEs, etc. Many studies have been performed by using these data. It has to be pointed out that the observed speed, angular width, and other parameters of CMEs by the LASCO are all the projections of their real values on the celestial plane, i.e., the apparent speed, apparent angular width, etc. Sunspots are considered as the phenomenon of the magnetic flux emerging from the photosphere, the number of sunspots commonly exhibits two peak values in one solar cycle, Gnevyshev[6−7] studied the physical mechanism of the two peak values in the sunspot numbers observed for one solar cycle. CMEs are a kind of very violent solar activities, for clarifying whether CMEs are synchronized with the variation of sunspot number, Kane[8] classified CMEs according to their angular widths, the CMEs with the angular widths of 0◦ ∼ 35◦ are defined as very weak CMEs, the CMEs with the angular widths of 36◦ ∼ 70◦ are defined as weak CMEs, those with the angular widths of 70◦ ∼ 105◦ are defined as strong CMEs, and those with the angular widths larger than 105◦ are defined as very strong CMEs. The research shows that the very weak and weak CMEs are not synchronized with the variation of sunspot number, and the double-peaked number distribution does not appear in the strong and very strong CMEs. It is noteworthy that Reference [8] has not studied the CME number distribution in the whole 23rd solar cycle, the studied time interval covers only 1997-2003, not a full solar cycle. There were a huge number of CMEs observed in the 23rd cycle, the angular widths of these CMEs were all in the range of 0◦ ∼ 360◦ . This paper has made a statistical analysis on the CME number distribution with the angular width and its feature in the whole 23rd solar cycle, studied the double-peaked distribution and the feature of the strong CMEs, especially the CMEs with the angular width of 360◦ , and selected the CMEs with some typical angular widths to make comparison with the time-variation feature of sunspot number. To simplify the analysis and make the analyzed result meaningful, the main ranges of the angular widths are selected as 0◦ ∼ 60◦ , 61◦ ∼ 120◦ , 121◦ ∼ 180◦ , 181◦ ∼ 240◦ , 241◦ ∼ 300◦ , 301◦ ∼ 359◦ , and 360◦ to perform the statistical analysis in this paper.
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
87
2. DATA ANALYSIS According to the CME list of LASCO, the numbers of CMEs with different angular widths can be obtained, after some rearrangement and analysis, the obtained information of the CMEs with different angular widths is listed in Table 1. From this table we can find clearly that in the period of 1996-2008, the CMEs with the angular widths of 0◦ ∼ 60◦ occupied 71.04% of all the CMEs, and the number of CMEs with the angular widths of 61◦ ∼ 120◦ occupied 20.06% of the total number of CMEs. This result shows that the CMEs with the angular widths of 0◦ ∼ 120◦ occupies over 91% of all the CMEs, and the ratio of CMEs with the angular widths of 121◦ ∼ 360◦ is lower than 9%, in which the ratio of CMEs with the angular widths of 121◦ ∼ 180◦ is 4.38%, the ratio of CMEs with the angular widths of 360◦ is 2.83%, and the least ratio is the CME number with the angular widths of 301◦ ∼ 359◦, it occupies only 0.04% of the total number. Table 1
Statistical information of CMEs with different angular widths during the 23rd solar cycle (1996-2008)
Year 0◦ ∼ 60◦ 61◦ ∼ 120◦ 121◦ ∼ 180◦ 181◦ ∼ 240◦ 241◦ ∼ 300◦ 301◦ ∼ 359◦ 1996 156 34 9 2 0 0 1997 228 115 16 4 1 0 1998 445 201 25 8 5 1 1999 549 327 84 22 7 0 2000 1058 425 94 21 3 0 2001 882 405 105 34 10 0 2002 1136 387 91 23 9 2 2003 757 272 51 13 7 0 2004 743 245 57 13 3 1 2005 912 201 52 19 6 0 2006 911 97 13 8 3 0 2007 1357 70 8 1 1 2 2008 819 31 9 2 1 0 total number 9953 2810 614 170 56 6 total ratio/(%) 71.04 20.06 4.38 1.12 0.39 0.04
360◦ 0◦ ∼ 360◦ 4 206 17 384 29 714 27 1016 58 1659 63 1499 52 1700 30 1130 40 1102 59 1249 14 1046 3 1442 1 863 397 14010 2.83 100
The time variations of the annually total number of CMEs and the annually mean number of sunspots are compared in Fig.1, it can be seen from both Table 1 and Fig.1 that there are three peak values of the annually total number of CMEs, the first peak value is 1659 appeared in 2000, the second peak value is 1700 appeared in 2002, and the third peak value is 1442 appeared in 2007. The comparison of time variation between the total CME number with the angular widths of 0◦ ∼ 60◦ and the mean sunspot number is shown in Fig.2, it can be seen from both Table 1 and Fig.2 that there are three peak values of the annually total number of CMEs with the angular widths of 0◦ ∼ 60◦ , the first peak value is 1058 appeared in 2000, the second peak value is 1136 appeared in 2002, the time interval between the first and second peaks is two years, and the third peak value, also the largest peak value, is 1357 appeared in 2007, which is rather abnormal, because the solar activity level in 2007 was very low, to produce so many CMEs in such a condition of low solar activity is very peculiar.
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Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
Fig. 1
Fig. 2
Comparison of the average numbers of sunspots (a) and CMEs (b) in different years
Comparison of the average numbers of sunspots (a) and CMEs with the angular widths of 0◦ ∼ 60◦ (b) in different years
The CMEs with the angular widths of 71◦ ∼ 105◦ were called the strong CMEs in Reference [8], and it was pointed out that there was no evident double-peaked structure for the strong CMEs. Because only the CMEs in the period of 1997-2003 were analyzed by Reference [8], hence, it is not sure whether the double-peaked structure exists or not for all the strong CMEs in the whole 23rd solar cycle. Fig.3 gives the comparison between the annually total number of CMEs with the angular widths of 121◦ ∼ 180◦ and the annually mean number of sunspots. It can be seen from Fig.3 that there is actually no double-peaked structure existed in the number distribution of CMEs with the angular widths of 121◦ ∼ 180◦ in the whole 23rd solar cycle, which is consistent with the result of Reference [8] that there was no evident double-peaked structure for the strong CMEs.
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
Fig. 3
Fig. 4
89
Comparison of the average numbers of sunspots (a) and CMEs with the angular widths of 121◦ ∼ 180◦ (b) in different years
Comparison of the average numbers of sunspots (a) and full-halo CMEs (b) in different years
The CME with the angular width of 360◦ is also called the full-halo CME, the comparison of the annually total number of full-halo CMEs and the annually mean number of sunspots is shown in Fig.4, it can be seen in both Table 1 and Fig.4 that there are two peak values for the full-halo CME numbers, the first peak value is 63 appeared in 2001, the second peak value is 59 appeared in 2005, and the time interval between the two peak values is four years. 3. CONCLUSION AND DISCUSSION From the statistical analysis of the CME numbers with different angular widths in the period of 1996-2008, the conclusions can be obtained as follows.
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Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
The CMEs with the angular widths of 0◦ ∼ 60◦ , 61◦ ∼ 120◦ , 121◦ ∼ 180◦ , 181◦ ∼ 240◦ , 241 ∼ 300◦ , 301◦ ∼ 359◦ , and 360◦ occupy respectively 71.04%, 20.06%, 4.38%, 1.12%, 0.39%, 0.04%, and 2.83% of the total CMEs. There are three peak values in the annually total numbers of CMEs with the angular widths of 0◦ ∼ 60◦ , the first peak value just coincident with the maximum year of the 23rd solar cycle, the second peak value at 2002, and the third peak value at 2007 while a very low level of solar activity. There is no doublepeaked structure in the distribution of CME numbers for the CMEs with the angular widths of 121◦ ∼ 180◦ . But there are evidently two peak values in the distribution of CME numbers for the full-halo CMEs, the first peak value appeared in 2001, the second peak value appeared in 2005, and the time interval is four years between these two peak values. The opinion that there is no double-peaked structure in the CME number distribution for the CMEs with the angular widths of 121◦ ∼ 180◦ is consistent with that there was no double-peaked structure for the strong CMEs in Reference [8]. Because the second peak value for the full-halo CMEs is located at 2005, but only the CMEs in the period of 1997-2003 were analyzed by Reference [8], which may be the reason why the double-peaked structure did not be found in the time variation of the full-halo CME number by Reference [8]. The analysis in this paper shows that even the double- or triple-peaked distribution does exist, the steps of the time variations of the CMEs with different angular widths are also inconsistent. The annually mean sunspot number is used in this paper, and the CME number refers to the total number in one year, hence, the first peak value of the annually total number for the CMEs with all angular widths in Fig.1 and that for the CMEs with the angular widths of 0◦ ∼ 60◦ are always coincident with the maximum year of solar activity. The first peak value for the full-halo CMEs appeared at the time later than the maximum year of the 23rd solar cycle, which is just consistent with the conclusion obtained by Yan et al.[9] that the peak value of solar flares was later than that of sunspot numbers. If we want to study the phase difference between the time evolutions of the CME and sunspot numbers, we have to use the monthly averaged numbers of CMEs, this remains to be studied further in the future. About 32% of CMEs are difficult to confirm by the coronagraphs with a large field of view[10] , thus the statistics in this paper can not include the information of this part of CMEs. However, it can be seen from the statistics of this paper that the CMEs with the angular widths of 0◦ ∼ 120◦ have occupied over 91% of the total CMEs, thus the statistical result and comparison between the time variations of the CME and sunspot numbers in this paper are believable. CMEs, especially the full-halo CMEs, are the main disturbing sources of the space weather, all the very large magnetic storms are always related to the full-halo CMEs[4] . Many features of the full-halo CMEs, such as the fast speed[11] , and the good directivity to the Earth, can be used for the prediction of magnetic storms[12] . Therefore, the study on CMEs and especially on the full-halo CMEs is very important. ◦
ACKNOWLEDGEMENT The data of CMEs in this paper are taken from http://cdaw. gsfc.nasa.gov/CME list/, and the data of sunspot numbers are taken from http://sidc.oma.be.
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
References 1
Gosling J. T., McComas D. J., Phillips J. L., Bame S. J., JGR., 1991, 96, 7831
2
Tsurutani B. T., Gonzalez W. D., Storms Geophys. Monog., 1997, 98, 77
3
Richardson I. G., Cliver E. W., Cane H. V., GeoRL., 2001, 28, 2569
4
Zhang J., Richardson G., Webb D. F., JGR., 2007, 112, A10102
5
Reames D. V., SSRv., 1999, 90, 413
6
Gnevyshev M. N., SoPh., 1967, 1, 107
7
Gnevyshev M. N., SoPh., 1977, 51, 175
8
Kane R. P., SoPh., 2008, 249, 369
9
Yan X. L., Deng L. H., Qu Z. Q., Xu C. L., Ap&SS., 2011, 333, 11
10
Wang Y., Chen C., Gui B., Shen C., Ye P., Wang S., JGR., 2011, 116, A04104
11
Zhang Q. M., Guo Y., Chen P. F., Ding M. D., Fang C., RAA., 2010, 10, 461
12
Kim R. S., Cho K. S., Moon Y. J., et al., JGR., 2005, 110, A11104
91
ELSEVIER
Chinese Astronomy and Astrophysics 38 (2014) 85–91
Distribution of CMEs with Different Angular Widths and Comparison with the Phase of Sunspot Number in the 23rd Solar Cycle † MENG Wei-juan1,2 LE Gui-ming1,2 LIN Zhao-xiang1 ZHANG Yong2,3 YANG Xing-xing2,3 1
2
South-Center University for Nationalities, Wuhan 430074 National Satellite Meteorology Center for Space Weather, China Meteorological Administration, Beijing 100081 3 Nanjing University of Information Science and Technology, Nanjing 210044
Abstract The variation of the number of coronal mass ejections (CMEs) with different angular widths in the period of 1996-2008 is analyzed statistically in this paper, together with a comparison of the feature of time variation between the number of CMEs with some typical angular widths and the number of sunspots. The analyzed result indicates that the number of CMEs with the angular widths of 0◦ ∼ 180◦ occupies an over 95% proportion in the total number of CMEs, the full-halo CMEs takes a proportion of 2.83%, and the number of CMEs with the angular widths of 301◦ ∼ 359◦ is very small. There are three peaks in the number distribution of CMEs with the angular widths of 0◦ ∼ 60◦ , which is not coincident with the feature of the time variation of sunspot number. There is no double-peaked number distribution for the CMEs with the angular widths of 121◦ ∼ 180◦. The number distribution of the full-halo CMEs has double peaks evidently, with the first peak value at 2001, and the second peak value at 2005, which is not synchronized with the variation of sunspot number. Key words: solar activities–coronal mass ejections (CMEs)—angular width— sunspot number
†
Supported by National Natural Science Foundation Received 2012–12–03; revised version 2013–02–17 A translation of Chin. J. Space Sci. Vol. 33, No. 3, pp. 225–230, 2013 [email protected]. Corresponding author: LE Gui-ming, [email protected]
0275-1062/14/$-see front matter 2014 Elsevier All rights reserved. c 2014B.V. 0275-1062/01/$-see front © matter Elsevier Science B. V. All rights reserved. doi:10.1016/j.chinastron.2014.01.008 PII:
86
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
1. INTRODUCTION The coronal mass ejection (CME) indicates such a phenomenon that a great amount of mass escaped from the solar corona, and entered into the interplanetary space, and it belongs to a kind of very violent solar activity. Some CMEs may produce coronal shocks when they are moving in the solar corona, which accelerate charged particles and result in the solar energetic particle events. After the CME entered into the interplanetary space, it becomes an interplanetary CME (ICME), when the ICME and its driving shock arrived in the magnetosphere, they may cause magnetic storm if the dynamic pressure and the southward magnetic field are strong enough, and thus to produce a disastrous space weather. A majority of large magnetic storms are caused by CMEs[1−3] , and the interplanetary sources of most large magnetic storms in the 23rd solar cycle are CMEs[4] . The large slow-varying solar energetic particle events are also correlated with ICMEs[5] , hence, CMEs are the main disturbing sources for the space weather, and therefore become a focal point in the research. Since the coronagraph LASCO with a large field of view on board of the SOHO satellite started to observe CMEs, a lot of observed data of CMEs have been obtained, including a series of information about the speed and angular width of CMEs, etc. Many studies have been performed by using these data. It has to be pointed out that the observed speed, angular width, and other parameters of CMEs by the LASCO are all the projections of their real values on the celestial plane, i.e., the apparent speed, apparent angular width, etc. Sunspots are considered as the phenomenon of the magnetic flux emerging from the photosphere, the number of sunspots commonly exhibits two peak values in one solar cycle, Gnevyshev[6−7] studied the physical mechanism of the two peak values in the sunspot numbers observed for one solar cycle. CMEs are a kind of very violent solar activities, for clarifying whether CMEs are synchronized with the variation of sunspot number, Kane[8] classified CMEs according to their angular widths, the CMEs with the angular widths of 0◦ ∼ 35◦ are defined as very weak CMEs, the CMEs with the angular widths of 36◦ ∼ 70◦ are defined as weak CMEs, those with the angular widths of 70◦ ∼ 105◦ are defined as strong CMEs, and those with the angular widths larger than 105◦ are defined as very strong CMEs. The research shows that the very weak and weak CMEs are not synchronized with the variation of sunspot number, and the double-peaked number distribution does not appear in the strong and very strong CMEs. It is noteworthy that Reference [8] has not studied the CME number distribution in the whole 23rd solar cycle, the studied time interval covers only 1997-2003, not a full solar cycle. There were a huge number of CMEs observed in the 23rd cycle, the angular widths of these CMEs were all in the range of 0◦ ∼ 360◦ . This paper has made a statistical analysis on the CME number distribution with the angular width and its feature in the whole 23rd solar cycle, studied the double-peaked distribution and the feature of the strong CMEs, especially the CMEs with the angular width of 360◦ , and selected the CMEs with some typical angular widths to make comparison with the time-variation feature of sunspot number. To simplify the analysis and make the analyzed result meaningful, the main ranges of the angular widths are selected as 0◦ ∼ 60◦ , 61◦ ∼ 120◦ , 121◦ ∼ 180◦ , 181◦ ∼ 240◦ , 241◦ ∼ 300◦ , 301◦ ∼ 359◦ , and 360◦ to perform the statistical analysis in this paper.
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
87
2. DATA ANALYSIS According to the CME list of LASCO, the numbers of CMEs with different angular widths can be obtained, after some rearrangement and analysis, the obtained information of the CMEs with different angular widths is listed in Table 1. From this table we can find clearly that in the period of 1996-2008, the CMEs with the angular widths of 0◦ ∼ 60◦ occupied 71.04% of all the CMEs, and the number of CMEs with the angular widths of 61◦ ∼ 120◦ occupied 20.06% of the total number of CMEs. This result shows that the CMEs with the angular widths of 0◦ ∼ 120◦ occupies over 91% of all the CMEs, and the ratio of CMEs with the angular widths of 121◦ ∼ 360◦ is lower than 9%, in which the ratio of CMEs with the angular widths of 121◦ ∼ 180◦ is 4.38%, the ratio of CMEs with the angular widths of 360◦ is 2.83%, and the least ratio is the CME number with the angular widths of 301◦ ∼ 359◦, it occupies only 0.04% of the total number. Table 1
Statistical information of CMEs with different angular widths during the 23rd solar cycle (1996-2008)
Year 0◦ ∼ 60◦ 61◦ ∼ 120◦ 121◦ ∼ 180◦ 181◦ ∼ 240◦ 241◦ ∼ 300◦ 301◦ ∼ 359◦ 1996 156 34 9 2 0 0 1997 228 115 16 4 1 0 1998 445 201 25 8 5 1 1999 549 327 84 22 7 0 2000 1058 425 94 21 3 0 2001 882 405 105 34 10 0 2002 1136 387 91 23 9 2 2003 757 272 51 13 7 0 2004 743 245 57 13 3 1 2005 912 201 52 19 6 0 2006 911 97 13 8 3 0 2007 1357 70 8 1 1 2 2008 819 31 9 2 1 0 total number 9953 2810 614 170 56 6 total ratio/(%) 71.04 20.06 4.38 1.12 0.39 0.04
360◦ 0◦ ∼ 360◦ 4 206 17 384 29 714 27 1016 58 1659 63 1499 52 1700 30 1130 40 1102 59 1249 14 1046 3 1442 1 863 397 14010 2.83 100
The time variations of the annually total number of CMEs and the annually mean number of sunspots are compared in Fig.1, it can be seen from both Table 1 and Fig.1 that there are three peak values of the annually total number of CMEs, the first peak value is 1659 appeared in 2000, the second peak value is 1700 appeared in 2002, and the third peak value is 1442 appeared in 2007. The comparison of time variation between the total CME number with the angular widths of 0◦ ∼ 60◦ and the mean sunspot number is shown in Fig.2, it can be seen from both Table 1 and Fig.2 that there are three peak values of the annually total number of CMEs with the angular widths of 0◦ ∼ 60◦ , the first peak value is 1058 appeared in 2000, the second peak value is 1136 appeared in 2002, the time interval between the first and second peaks is two years, and the third peak value, also the largest peak value, is 1357 appeared in 2007, which is rather abnormal, because the solar activity level in 2007 was very low, to produce so many CMEs in such a condition of low solar activity is very peculiar.
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Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
Fig. 1
Fig. 2
Comparison of the average numbers of sunspots (a) and CMEs (b) in different years
Comparison of the average numbers of sunspots (a) and CMEs with the angular widths of 0◦ ∼ 60◦ (b) in different years
The CMEs with the angular widths of 71◦ ∼ 105◦ were called the strong CMEs in Reference [8], and it was pointed out that there was no evident double-peaked structure for the strong CMEs. Because only the CMEs in the period of 1997-2003 were analyzed by Reference [8], hence, it is not sure whether the double-peaked structure exists or not for all the strong CMEs in the whole 23rd solar cycle. Fig.3 gives the comparison between the annually total number of CMEs with the angular widths of 121◦ ∼ 180◦ and the annually mean number of sunspots. It can be seen from Fig.3 that there is actually no double-peaked structure existed in the number distribution of CMEs with the angular widths of 121◦ ∼ 180◦ in the whole 23rd solar cycle, which is consistent with the result of Reference [8] that there was no evident double-peaked structure for the strong CMEs.
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
Fig. 3
Fig. 4
89
Comparison of the average numbers of sunspots (a) and CMEs with the angular widths of 121◦ ∼ 180◦ (b) in different years
Comparison of the average numbers of sunspots (a) and full-halo CMEs (b) in different years
The CME with the angular width of 360◦ is also called the full-halo CME, the comparison of the annually total number of full-halo CMEs and the annually mean number of sunspots is shown in Fig.4, it can be seen in both Table 1 and Fig.4 that there are two peak values for the full-halo CME numbers, the first peak value is 63 appeared in 2001, the second peak value is 59 appeared in 2005, and the time interval between the two peak values is four years. 3. CONCLUSION AND DISCUSSION From the statistical analysis of the CME numbers with different angular widths in the period of 1996-2008, the conclusions can be obtained as follows.
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Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
The CMEs with the angular widths of 0◦ ∼ 60◦ , 61◦ ∼ 120◦ , 121◦ ∼ 180◦ , 181◦ ∼ 240◦ , 241 ∼ 300◦ , 301◦ ∼ 359◦ , and 360◦ occupy respectively 71.04%, 20.06%, 4.38%, 1.12%, 0.39%, 0.04%, and 2.83% of the total CMEs. There are three peak values in the annually total numbers of CMEs with the angular widths of 0◦ ∼ 60◦ , the first peak value just coincident with the maximum year of the 23rd solar cycle, the second peak value at 2002, and the third peak value at 2007 while a very low level of solar activity. There is no doublepeaked structure in the distribution of CME numbers for the CMEs with the angular widths of 121◦ ∼ 180◦ . But there are evidently two peak values in the distribution of CME numbers for the full-halo CMEs, the first peak value appeared in 2001, the second peak value appeared in 2005, and the time interval is four years between these two peak values. The opinion that there is no double-peaked structure in the CME number distribution for the CMEs with the angular widths of 121◦ ∼ 180◦ is consistent with that there was no double-peaked structure for the strong CMEs in Reference [8]. Because the second peak value for the full-halo CMEs is located at 2005, but only the CMEs in the period of 1997-2003 were analyzed by Reference [8], which may be the reason why the double-peaked structure did not be found in the time variation of the full-halo CME number by Reference [8]. The analysis in this paper shows that even the double- or triple-peaked distribution does exist, the steps of the time variations of the CMEs with different angular widths are also inconsistent. The annually mean sunspot number is used in this paper, and the CME number refers to the total number in one year, hence, the first peak value of the annually total number for the CMEs with all angular widths in Fig.1 and that for the CMEs with the angular widths of 0◦ ∼ 60◦ are always coincident with the maximum year of solar activity. The first peak value for the full-halo CMEs appeared at the time later than the maximum year of the 23rd solar cycle, which is just consistent with the conclusion obtained by Yan et al.[9] that the peak value of solar flares was later than that of sunspot numbers. If we want to study the phase difference between the time evolutions of the CME and sunspot numbers, we have to use the monthly averaged numbers of CMEs, this remains to be studied further in the future. About 32% of CMEs are difficult to confirm by the coronagraphs with a large field of view[10] , thus the statistics in this paper can not include the information of this part of CMEs. However, it can be seen from the statistics of this paper that the CMEs with the angular widths of 0◦ ∼ 120◦ have occupied over 91% of the total CMEs, thus the statistical result and comparison between the time variations of the CME and sunspot numbers in this paper are believable. CMEs, especially the full-halo CMEs, are the main disturbing sources of the space weather, all the very large magnetic storms are always related to the full-halo CMEs[4] . Many features of the full-halo CMEs, such as the fast speed[11] , and the good directivity to the Earth, can be used for the prediction of magnetic storms[12] . Therefore, the study on CMEs and especially on the full-halo CMEs is very important. ◦
ACKNOWLEDGEMENT The data of CMEs in this paper are taken from http://cdaw. gsfc.nasa.gov/CME list/, and the data of sunspot numbers are taken from http://sidc.oma.be.
Meng Wei-juan et al. / Chinese Astronomy and Astrophysics 38 (2014) 85–91
References 1
Gosling J. T., McComas D. J., Phillips J. L., Bame S. J., JGR., 1991, 96, 7831
2
Tsurutani B. T., Gonzalez W. D., Storms Geophys. Monog., 1997, 98, 77
3
Richardson I. G., Cliver E. W., Cane H. V., GeoRL., 2001, 28, 2569
4
Zhang J., Richardson G., Webb D. F., JGR., 2007, 112, A10102
5
Reames D. V., SSRv., 1999, 90, 413
6
Gnevyshev M. N., SoPh., 1967, 1, 107
7
Gnevyshev M. N., SoPh., 1977, 51, 175
8
Kane R. P., SoPh., 2008, 249, 369
9
Yan X. L., Deng L. H., Qu Z. Q., Xu C. L., Ap&SS., 2011, 333, 11
10
Wang Y., Chen C., Gui B., Shen C., Ye P., Wang S., JGR., 2011, 116, A04104
11
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