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Dependence of the Intensity of Solar Energetic Particle Event on the Twin-CME: A Study of Two Cases
CHINESE ASTRONOMY AND ASTROPHYSICS Chinese Astronomy and Astrophysics 41 (2017) 62–67
Dependence of the Intensity of Solar Energetic Particle Event on the Twin-CME: A Study of Two Cases CHEN Min-hao1
CHEN Yu-lin1 LI Zhong-yi1
1
LE Gui-ming2,3
LU Yang-ping1
YIN Zhi-qiang4
School of Mathematics and Statistics, Nanjing University of Information Science and Technology, Nanjing 210044 2 3
Key laboratory of Space Weather, China Meteorological Administration, Beijing 100081
National Center for Space Weather, China Meteorological Administration, Beijing 100081 4
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
Abstract Solar energetic particle events often associate with solar flares and Coronal Mass Ejections (CMEs). Because that the interaction of twin-CME is the key factor of solar energetic particle (SEP) events, the relationship between the intensity of SEP event and the associated twin-CME has been investigated for the two SEP events occurred respectively on 15 April 2001 and 20 January 2005, by using the energetic particle strength, flare intensity, and the relative height and time of CMEs observed by the SOHO satellite, as well as the CME speed obtained by fitting the height variation with the time. The results show that the intensities of the two SEP events have no relationship with the associated twin-CME. Hence, in the earlier stage of these two SEP events, the protons of E≥10 MeV are only associated with relevant solar flares and CMEs. Key words Sun: energetic particle event—Sun: coronal mass ejection—Sun: particle acceleration 1.
INTRODUCTION
A large gradual solar energetic particle (SEP) event means the SEP event associated with solar flare and coronal mass ejection (CME), and its integrated flux of protons of E≥10 MeV is continuously above 10 pfu in a duration not shorter than 15 min. There have been a great Received 2015–03–25; revised version 2015–07–09
A translation of Chin. J. Space Sci. Vol. 36, No. 3, pp. 267–271, 2016 firefl[email protected]
0275-1062/16/$-see front matter © 2017 Elsevier B.V. All rights reserved. doi:10.1016/j.chinastron.2017.01.010
CHEN Min-hao et al. / Chinese Astronomy and Astrophysics 41 (2017) 62–67
63
amount of studies performed on these large and gradual SEP events[1,2] . Because that during a large gradual SEP event there are often two CMEs continuously erupted within 24 hours in the same active region, and the angular width and speed of the second CME are always larger than those of the first one, thus it is possible for the second CME to overlap and interact with the first one. Based on this phenomenon, Gopalswamy et al.[1] proposed that the interaction of CMEs is the key factor for the occurrence of these large gradual SEP events. According to this observational phenomenon, Ding et al.[2] found by statistics that most of large gradual SEP events are always associated with two CMEs erupted successively in a time interval smaller than 9 hours. In this paper, for the sake of convenience, we define the two CMEs erupted successively in the same active region within 9 hours to be CME 1 and CME 2, and the angular width and speed of CME 2 are always larger than those of CME 1, and such a phenomenon is defined as a twin-CME event. Gopalswamy et al.[3] suggested that the twin-CME event is the key factor for the occurrence of large gradual SEP events, but this opinion was not supported by some studies. Li et al[4] reported some energetic particle ground level enhancement events (GLEs), and compared the peak time of relativistic particle event with the interacting time of twin-CME, they found that when CME 2 and CME 2 are overlapped, the peak value of GLE or sub-relativistic particle event has happened already in advance, hence the GLEs or sub-relativistic particle events are not associated with the interaction of twin-CME. The disturbed environment caused by the shock of CME 1 is more favorable to the particle acceleration of the shock driven by CME 2, and thus to cause the appearance of strong SEP events[1,2] . Though the CMEs erupted successively within 9 hours were observed by LASCO, but the strong SEP events were not detected. Ding et al.[2] suggested that the reason for this situation is that CME 2 might be not moving along the trajectory of CME 1, which makes CME 2 move outward, and the scanned area is not the disturbed region caused by CME 1; while LASCO/SOHO only provides the 2-D images, and the twin-CME events appeared in these images might be not the real ones; and whether a large SEP event occurs is also related to the morphology and strength of the shock driven by CME 2. Richardson et al.[5] suggested that the twin-CME events observed by LASCO/SOHO can not make sure of the spatially overlapping of the two CMEs. If the two CMEs are finally not spatially overlapped, which means that the propagating trajectories of the two CMEs are not identical, this is also the reason why Gopalswamy et al. suspected the correlation between the interaction of CMEs and the SEP event. The SEP event on 2013 May 22 was associated with a twin-CME, which was found by the 3D reconstruction of the CME data observed by multiple satellites, and the two CMEs associated with the SEP event of 2013 May 22 were actually overlapped in space. When CME 2 was overlapped with CME 1, a sudden and significant enhancement of the integrated flux of protons of E≥10 MeV appeared, but the variation of the integrated flux of protons of E≥100 MeV was very small. This event shows that for the twin-CME event, CME 2 is really possible to overlap with CME 1, due
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CHEN Min-hao et al. / Chinese Astronomy and Astrophysics 41 (2017) 62–67
to the stronger shock driven by CME 2, when CME 2 is overlapped with CME 1, an evident enhancement of the integrated flux of low-energy protons should appear, thus it may be a criterion to see whether CME 2 is really overlapped with CME 1 in spatial position. There were a lot of large SEP events in the 23rd solar cycle, in which about 73% of SEP events in the solar western hemisphere belonged to the Twin-CME events[2] . Richardson et al.[3] suggested that the relativistic protons are not associated with the twin-CME events. However, for these twin-CME events, when CME 2 is overlapped with CME 1, whether an evident enhancement of the integrated flux of protons of E≥10 MeV appears, and whether the impulsive phase of the integrated flux of protons of E≥10 MeV appears before or after the interacting time of two CMEs, these are important topics in the study of solar SEP events, because the twin-CME events and the intensity of SEP events are related to the origin of SEP events. Richardson et al.[3] have studied and analyzed the relationship between relativistic protons and twin-CME events, for the two events whose source regions were positioned on the solar western hemisphere, this paper studies the relationship between the features of intensity variations of these two SEP events and the twin-CME events, i.e., the relationship between the twin-CME event and the intensity variation of protons of E≥10 MeV, thus to analyze in-depth the relationship between the twin-CME event and the intensity of lowerenergy protons. 2.
EVENT ANALYSIS
On 2005 January 20, an X7.1-class flare erupted in the active region 10720 positioned at 14◦ N and 61◦ W on the solar surface, the start time of the flare was 06:36 UT, the peak time was 07:01 UT, and the end time was 07:26 UT, the flare was accompanied by a CME with the speed of 3242 km·s−1[6] . When Ding et al.[2] analyzed statistically the relationship between the twin-CME events and the large gradual SEP events, they gave the twin-CME in the SEP event of 2005 January 20 to be respectively CME 1 at 04:06 UT with the speed of 503 km·s−1 and the angular width of 18◦ , and CME 2 at 06:54 UT with the speed of 3242 km·s−1[2] . After the X7.1-class flare and CME 2 erupted, the proton flux of E≥10 MeV enhanced rapidly, in which the proton flux of E≥100 MeV reached the maximum 481 pfu at 07:45 UT, while the proton flux of E≥10 MeV enhanced rapidly up to 1550 pfu at 07:45 UT. According to the variation of the height of the twin-CME event with the time, Fig.1 shows the heights of CME 1 and CME 2 as a function of time, simultaneously gives the variations of the 1∼8˚ A soft X-ray flux, the proton fluxes of E≥10 MeV and E≥100 MeV, observed by the GOES satellite. From Fig.1 we can find that after the flare erupted, the proton flux of E≥100 MeV enhanced rapidly up to the maximum of 481 pfu at 07:45 UT. In this duration the proton flux of E≥10 MeV also enhanced rapidly to form the impulsive phase of SEP. It is obvious that the time of impulsive phase of the SEP event was earlier than the overlapped time of CME 2 and CME 1, which means that the interaction of two CMEs did not affect the
CHEN Min-hao et al. / Chinese Astronomy and Astrophysics 41 (2017) 62–67
65
impulsive phase of this SEP event. In addition, when CME 2 was overlapped and interacted with CME 1, the proton flux of E≥10 MeV did not occur an obvious enhancement as that of the event on 2013 May 22. If the relativistic protons in the SEP event of 2005 January 20 were accelerated by shock, then in this event the intensity of the shock driven by CME 2 should be much stronger than that driven by CME 2 in the SEP event of 2013 May 22, thus for the SEP event of 2005 January 20, if CME 2 can overlap with CME 1, the interaction of two CMEs may cause very significant variation of the intensity of protons of E≥10 MeV, but such a phenomenon did not appear in Fig.1. This implies that CME 2 did not overlap with CME 1 in space, i.e., CME 2 did not interact with CME 1.
Fig. 1 The SEP event on 2005 January 20, and the accompanied soft X-ray flare and twin-CME event
On 2001 April 15, an X14-class flare erupted in the active region 9415 positioned at 20 S and 85◦ W on the solar surface, the flare was accompanied by CME 2 with the speed of 1199 km·s−1 at 14:06 UT. Another CME (CME 1) related to this SEP event erupted at 11:18 UT with the speed of 511 km·s−1 , evidently less than the speed of CME 2. Fig.2 gives the time variation of the soft X-ray flux at 1∼8˚ A observed by the GOES satellite, as well as the intensity variations of the protons of E≥10 MeV and E≥100 MeV. It can be seen from Fig.2 that the impulsive phase of this SEP event is earlier than the time when the two CMEs met together. When CME 2 was overlapped with CME 1, the proton flux of E≥10 MeV did not have an obvious change, which means that CME 2 did not really overlap with CME 1. ◦
3.
CONCLUSION AND DISCUSSION
Through analyzing the relationship between the intensities of two SEP events in the solar western heliosphere and their accompanied CMEs, it is found that when the faster CME
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was overlapped with the slower CME, the flux of protons of E≥100 MeV already reached its peak value, while the impulsive phase of proton flux of E≥10 MeV also occurred before the overlapped time, moreover, when CME 2 was overlapped with CME 1, the flux of protons of E≥100 MeV did not appear an obvious change. In order to understand in-depth the relationship between these two SEP events and twin-CME events, we have compared the parameters of twin-CME events relevant to these two SEP events with the parameters of the flare and twin-CME in the SEP event on 2013 May 22, and the results are listed in Table 1, in which v1 and AW1 are respectively the speed and angular width of the slower CME in the twin-CME, while v2 and AW2 are respectively the speed and angular width of the faster CME in the twin-CME, and Δt is the time difference between the slower CME and faster CME.
Fig. 2 The SEP event on 15 April 2001, and the accompanied soft X-ray flare and twin-CME event
Table 1 Comparisons of the flares and twin-CMEs associated with the SEP events No.
Date
GLE
Location
Class
/(◦ )
v1
AW1
/(km/s)
/(◦ )
v2
AW2
Δt
/(km/s)
/(◦ )
/(h)
1
2001-04-15
Yes
20S, 85W
X14
511
70
1199
167
2.8
2
2005-01-20
Yes
14N, 61W
X7.1
503
301
3242
360
2.8
3
2013-05-22
No
15N, 70W
M5.0
519
210
1466
360
4.5
It can be seen from Table 1 that the first and second SEP events are all the relativistic SEP events. If the relativistic protons are accelerated by the shock driven by a CME, the shock driven by CME 2 in the first and second SEP events should be very strong, and much stronger than the shock intensity driven by CME 2 in the third SEP event, as shown in
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Table 1. No matter whether the twin-CME event on 2005 January 20 or the twin-CME event on 2001 April 15, when CME 2 was overlapped with CME 1, there was no obvious variation appeared in the intensity of protons of E≥10 MeV. There are only two possibilities: one is that the propagating trajectory of CME 1 is different from that of CME 2, which makes CME 2 unable to overlap with CME 1, and thus no interaction happens in the two CMEs; and another one is that the shock driven by CME 2 is not strong, and when CME 2 is overlapped with CME 1, the shock driven by CME 2 is not capable to accelerate the protons of E≥10 MeV. Hence, in both cases mentioned above, the intensity variations of the SEP events on 2005 January 20 and 2001 April 15 are irrelevant to the twin-CME events. Through analyzing the relationship between the intensities of the SEP events on 2005 January 20 and 2001 April 15 and the relevant twin-CME events, it is found that in this two SEP events, the intensity of protons of E≥10 MeV is not correlated with the twinCME event. This result supports the opinion of Reference [4], and it is also consistent with the conclusion in Reference [7] about the relationship between the intensity of protons of E≥20 MeV and the twin-CME. Because the intensity of protons of E≥10 MeV is not correlated with the twin-CME in these two SEP events, in the earlier stage of these two SEP events the intensity of protons of E≥10 MeV is only correlated with the corresponding solar flare and CME. The studies need to be deepened further, in order to verify the result by more examples. ACKNOWLEDGEMENTS The data of solar soft X-ray and energetic particles are taken from the GOES satellite of National Oceanic and Atmospheric Administration (NOAA) of USA, the speeds and angular widths of CMEs are taken from the information given by the wide-field coronagraph LASCO on board of the SOHO satellite∗ . References 1
Gopalswamy N. S., Yashino G., Michaek M. L., et al., Astrophys. J., 2002, 572, 103-107
2
Ding L., Jiang Y., Zhao L., Li G., Astrophys. J., 2013, 763, article id. 30, 17 pp., DOI 10.1088/0004637X/763/1/30
3
Gopalswamy N. S., Xie H., Yashirob S., Coronal mass ejections and ground level enhancements, Proceedings of 29th International Cosmic Ray Conference. Pune, India: Tata Institute of Fundamental Research, 2005, 101-104
4
Li G., Moore R., Mewaldt R. A., Zhao L., Space Sci. Rev., 2012, 171, 141-160
5
Richardson I. G., Lawrence G. R., Dennis K. H., et al., Geophys. Res. Lett., 2003, 30, pp. SSC 5-1, DOI 10.1029/2003GL018042
6
Ding L., Li G., Jiang Y. et al., Astrophys. J., 2014, 793, article id. L35, 7 pp., DOI 10.1088/20418205/793/2/L35
7
Kahler S. W., Vourlidas A., Astrophys. J., 2014, 784, article id. 47, 10 pp., DOI 10.1088/0004637X/784/1/47 ∗ http://cdaw.gsfc.nasa.gov/CME
list/
Dependence of the Intensity of Solar Energetic Particle Event on the Twin-CME: A Study of Two Cases CHEN Min-hao1
CHEN Yu-lin1 LI Zhong-yi1
1
LE Gui-ming2,3
LU Yang-ping1
YIN Zhi-qiang4
School of Mathematics and Statistics, Nanjing University of Information Science and Technology, Nanjing 210044 2 3
Key laboratory of Space Weather, China Meteorological Administration, Beijing 100081
National Center for Space Weather, China Meteorological Administration, Beijing 100081 4
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
Abstract Solar energetic particle events often associate with solar flares and Coronal Mass Ejections (CMEs). Because that the interaction of twin-CME is the key factor of solar energetic particle (SEP) events, the relationship between the intensity of SEP event and the associated twin-CME has been investigated for the two SEP events occurred respectively on 15 April 2001 and 20 January 2005, by using the energetic particle strength, flare intensity, and the relative height and time of CMEs observed by the SOHO satellite, as well as the CME speed obtained by fitting the height variation with the time. The results show that the intensities of the two SEP events have no relationship with the associated twin-CME. Hence, in the earlier stage of these two SEP events, the protons of E≥10 MeV are only associated with relevant solar flares and CMEs. Key words Sun: energetic particle event—Sun: coronal mass ejection—Sun: particle acceleration 1.
INTRODUCTION
A large gradual solar energetic particle (SEP) event means the SEP event associated with solar flare and coronal mass ejection (CME), and its integrated flux of protons of E≥10 MeV is continuously above 10 pfu in a duration not shorter than 15 min. There have been a great Received 2015–03–25; revised version 2015–07–09
A translation of Chin. J. Space Sci. Vol. 36, No. 3, pp. 267–271, 2016 firefl[email protected]
0275-1062/16/$-see front matter © 2017 Elsevier B.V. All rights reserved. doi:10.1016/j.chinastron.2017.01.010
CHEN Min-hao et al. / Chinese Astronomy and Astrophysics 41 (2017) 62–67
63
amount of studies performed on these large and gradual SEP events[1,2] . Because that during a large gradual SEP event there are often two CMEs continuously erupted within 24 hours in the same active region, and the angular width and speed of the second CME are always larger than those of the first one, thus it is possible for the second CME to overlap and interact with the first one. Based on this phenomenon, Gopalswamy et al.[1] proposed that the interaction of CMEs is the key factor for the occurrence of these large gradual SEP events. According to this observational phenomenon, Ding et al.[2] found by statistics that most of large gradual SEP events are always associated with two CMEs erupted successively in a time interval smaller than 9 hours. In this paper, for the sake of convenience, we define the two CMEs erupted successively in the same active region within 9 hours to be CME 1 and CME 2, and the angular width and speed of CME 2 are always larger than those of CME 1, and such a phenomenon is defined as a twin-CME event. Gopalswamy et al.[3] suggested that the twin-CME event is the key factor for the occurrence of large gradual SEP events, but this opinion was not supported by some studies. Li et al[4] reported some energetic particle ground level enhancement events (GLEs), and compared the peak time of relativistic particle event with the interacting time of twin-CME, they found that when CME 2 and CME 2 are overlapped, the peak value of GLE or sub-relativistic particle event has happened already in advance, hence the GLEs or sub-relativistic particle events are not associated with the interaction of twin-CME. The disturbed environment caused by the shock of CME 1 is more favorable to the particle acceleration of the shock driven by CME 2, and thus to cause the appearance of strong SEP events[1,2] . Though the CMEs erupted successively within 9 hours were observed by LASCO, but the strong SEP events were not detected. Ding et al.[2] suggested that the reason for this situation is that CME 2 might be not moving along the trajectory of CME 1, which makes CME 2 move outward, and the scanned area is not the disturbed region caused by CME 1; while LASCO/SOHO only provides the 2-D images, and the twin-CME events appeared in these images might be not the real ones; and whether a large SEP event occurs is also related to the morphology and strength of the shock driven by CME 2. Richardson et al.[5] suggested that the twin-CME events observed by LASCO/SOHO can not make sure of the spatially overlapping of the two CMEs. If the two CMEs are finally not spatially overlapped, which means that the propagating trajectories of the two CMEs are not identical, this is also the reason why Gopalswamy et al. suspected the correlation between the interaction of CMEs and the SEP event. The SEP event on 2013 May 22 was associated with a twin-CME, which was found by the 3D reconstruction of the CME data observed by multiple satellites, and the two CMEs associated with the SEP event of 2013 May 22 were actually overlapped in space. When CME 2 was overlapped with CME 1, a sudden and significant enhancement of the integrated flux of protons of E≥10 MeV appeared, but the variation of the integrated flux of protons of E≥100 MeV was very small. This event shows that for the twin-CME event, CME 2 is really possible to overlap with CME 1, due
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CHEN Min-hao et al. / Chinese Astronomy and Astrophysics 41 (2017) 62–67
to the stronger shock driven by CME 2, when CME 2 is overlapped with CME 1, an evident enhancement of the integrated flux of low-energy protons should appear, thus it may be a criterion to see whether CME 2 is really overlapped with CME 1 in spatial position. There were a lot of large SEP events in the 23rd solar cycle, in which about 73% of SEP events in the solar western hemisphere belonged to the Twin-CME events[2] . Richardson et al.[3] suggested that the relativistic protons are not associated with the twin-CME events. However, for these twin-CME events, when CME 2 is overlapped with CME 1, whether an evident enhancement of the integrated flux of protons of E≥10 MeV appears, and whether the impulsive phase of the integrated flux of protons of E≥10 MeV appears before or after the interacting time of two CMEs, these are important topics in the study of solar SEP events, because the twin-CME events and the intensity of SEP events are related to the origin of SEP events. Richardson et al.[3] have studied and analyzed the relationship between relativistic protons and twin-CME events, for the two events whose source regions were positioned on the solar western hemisphere, this paper studies the relationship between the features of intensity variations of these two SEP events and the twin-CME events, i.e., the relationship between the twin-CME event and the intensity variation of protons of E≥10 MeV, thus to analyze in-depth the relationship between the twin-CME event and the intensity of lowerenergy protons. 2.
EVENT ANALYSIS
On 2005 January 20, an X7.1-class flare erupted in the active region 10720 positioned at 14◦ N and 61◦ W on the solar surface, the start time of the flare was 06:36 UT, the peak time was 07:01 UT, and the end time was 07:26 UT, the flare was accompanied by a CME with the speed of 3242 km·s−1[6] . When Ding et al.[2] analyzed statistically the relationship between the twin-CME events and the large gradual SEP events, they gave the twin-CME in the SEP event of 2005 January 20 to be respectively CME 1 at 04:06 UT with the speed of 503 km·s−1 and the angular width of 18◦ , and CME 2 at 06:54 UT with the speed of 3242 km·s−1[2] . After the X7.1-class flare and CME 2 erupted, the proton flux of E≥10 MeV enhanced rapidly, in which the proton flux of E≥100 MeV reached the maximum 481 pfu at 07:45 UT, while the proton flux of E≥10 MeV enhanced rapidly up to 1550 pfu at 07:45 UT. According to the variation of the height of the twin-CME event with the time, Fig.1 shows the heights of CME 1 and CME 2 as a function of time, simultaneously gives the variations of the 1∼8˚ A soft X-ray flux, the proton fluxes of E≥10 MeV and E≥100 MeV, observed by the GOES satellite. From Fig.1 we can find that after the flare erupted, the proton flux of E≥100 MeV enhanced rapidly up to the maximum of 481 pfu at 07:45 UT. In this duration the proton flux of E≥10 MeV also enhanced rapidly to form the impulsive phase of SEP. It is obvious that the time of impulsive phase of the SEP event was earlier than the overlapped time of CME 2 and CME 1, which means that the interaction of two CMEs did not affect the
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impulsive phase of this SEP event. In addition, when CME 2 was overlapped and interacted with CME 1, the proton flux of E≥10 MeV did not occur an obvious enhancement as that of the event on 2013 May 22. If the relativistic protons in the SEP event of 2005 January 20 were accelerated by shock, then in this event the intensity of the shock driven by CME 2 should be much stronger than that driven by CME 2 in the SEP event of 2013 May 22, thus for the SEP event of 2005 January 20, if CME 2 can overlap with CME 1, the interaction of two CMEs may cause very significant variation of the intensity of protons of E≥10 MeV, but such a phenomenon did not appear in Fig.1. This implies that CME 2 did not overlap with CME 1 in space, i.e., CME 2 did not interact with CME 1.
Fig. 1 The SEP event on 2005 January 20, and the accompanied soft X-ray flare and twin-CME event
On 2001 April 15, an X14-class flare erupted in the active region 9415 positioned at 20 S and 85◦ W on the solar surface, the flare was accompanied by CME 2 with the speed of 1199 km·s−1 at 14:06 UT. Another CME (CME 1) related to this SEP event erupted at 11:18 UT with the speed of 511 km·s−1 , evidently less than the speed of CME 2. Fig.2 gives the time variation of the soft X-ray flux at 1∼8˚ A observed by the GOES satellite, as well as the intensity variations of the protons of E≥10 MeV and E≥100 MeV. It can be seen from Fig.2 that the impulsive phase of this SEP event is earlier than the time when the two CMEs met together. When CME 2 was overlapped with CME 1, the proton flux of E≥10 MeV did not have an obvious change, which means that CME 2 did not really overlap with CME 1. ◦
3.
CONCLUSION AND DISCUSSION
Through analyzing the relationship between the intensities of two SEP events in the solar western heliosphere and their accompanied CMEs, it is found that when the faster CME
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was overlapped with the slower CME, the flux of protons of E≥100 MeV already reached its peak value, while the impulsive phase of proton flux of E≥10 MeV also occurred before the overlapped time, moreover, when CME 2 was overlapped with CME 1, the flux of protons of E≥100 MeV did not appear an obvious change. In order to understand in-depth the relationship between these two SEP events and twin-CME events, we have compared the parameters of twin-CME events relevant to these two SEP events with the parameters of the flare and twin-CME in the SEP event on 2013 May 22, and the results are listed in Table 1, in which v1 and AW1 are respectively the speed and angular width of the slower CME in the twin-CME, while v2 and AW2 are respectively the speed and angular width of the faster CME in the twin-CME, and Δt is the time difference between the slower CME and faster CME.
Fig. 2 The SEP event on 15 April 2001, and the accompanied soft X-ray flare and twin-CME event
Table 1 Comparisons of the flares and twin-CMEs associated with the SEP events No.
Date
GLE
Location
Class
/(◦ )
v1
AW1
/(km/s)
/(◦ )
v2
AW2
Δt
/(km/s)
/(◦ )
/(h)
1
2001-04-15
Yes
20S, 85W
X14
511
70
1199
167
2.8
2
2005-01-20
Yes
14N, 61W
X7.1
503
301
3242
360
2.8
3
2013-05-22
No
15N, 70W
M5.0
519
210
1466
360
4.5
It can be seen from Table 1 that the first and second SEP events are all the relativistic SEP events. If the relativistic protons are accelerated by the shock driven by a CME, the shock driven by CME 2 in the first and second SEP events should be very strong, and much stronger than the shock intensity driven by CME 2 in the third SEP event, as shown in
CHEN Min-hao et al. / Chinese Astronomy and Astrophysics 41 (2017) 62–67
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Table 1. No matter whether the twin-CME event on 2005 January 20 or the twin-CME event on 2001 April 15, when CME 2 was overlapped with CME 1, there was no obvious variation appeared in the intensity of protons of E≥10 MeV. There are only two possibilities: one is that the propagating trajectory of CME 1 is different from that of CME 2, which makes CME 2 unable to overlap with CME 1, and thus no interaction happens in the two CMEs; and another one is that the shock driven by CME 2 is not strong, and when CME 2 is overlapped with CME 1, the shock driven by CME 2 is not capable to accelerate the protons of E≥10 MeV. Hence, in both cases mentioned above, the intensity variations of the SEP events on 2005 January 20 and 2001 April 15 are irrelevant to the twin-CME events. Through analyzing the relationship between the intensities of the SEP events on 2005 January 20 and 2001 April 15 and the relevant twin-CME events, it is found that in this two SEP events, the intensity of protons of E≥10 MeV is not correlated with the twinCME event. This result supports the opinion of Reference [4], and it is also consistent with the conclusion in Reference [7] about the relationship between the intensity of protons of E≥20 MeV and the twin-CME. Because the intensity of protons of E≥10 MeV is not correlated with the twin-CME in these two SEP events, in the earlier stage of these two SEP events the intensity of protons of E≥10 MeV is only correlated with the corresponding solar flare and CME. The studies need to be deepened further, in order to verify the result by more examples. ACKNOWLEDGEMENTS The data of solar soft X-ray and energetic particles are taken from the GOES satellite of National Oceanic and Atmospheric Administration (NOAA) of USA, the speeds and angular widths of CMEs are taken from the information given by the wide-field coronagraph LASCO on board of the SOHO satellite∗ . References 1
Gopalswamy N. S., Yashino G., Michaek M. L., et al., Astrophys. J., 2002, 572, 103-107
2
Ding L., Jiang Y., Zhao L., Li G., Astrophys. J., 2013, 763, article id. 30, 17 pp., DOI 10.1088/0004637X/763/1/30
3
Gopalswamy N. S., Xie H., Yashirob S., Coronal mass ejections and ground level enhancements, Proceedings of 29th International Cosmic Ray Conference. Pune, India: Tata Institute of Fundamental Research, 2005, 101-104
4
Li G., Moore R., Mewaldt R. A., Zhao L., Space Sci. Rev., 2012, 171, 141-160
5
Richardson I. G., Lawrence G. R., Dennis K. H., et al., Geophys. Res. Lett., 2003, 30, pp. SSC 5-1, DOI 10.1029/2003GL018042
6
Ding L., Li G., Jiang Y. et al., Astrophys. J., 2014, 793, article id. L35, 7 pp., DOI 10.1088/20418205/793/2/L35
7
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