PROCEEDINGS OF THE 31 ST ICRC, LODZ 2009 1

Coronal mass ejections, cosmic ray neutron monitor intensity and interplanetary magnetic field Rajesh K. Mishra 1 and Rekha Agarwal 2 Computer and Information Technology Section, Tropical Forest Research Institute,P.O.: RFRC, Mandla Road, Jabalpur (M.P.) India 482 0212 Department of Physics, Govt. Model Science College (Autonomous),Jabalpur (M.P.) 482 001, India

Abstract. Coronal Mass Ejections are onset of CMEs and depressed 3 days vast structures of plasma and magnetic prior to the onset of CMEs, whereas in fields that are expelled from the sun case of asymmetric and complex full into the heliosphere. This material is CMEs, the intensity depressed 2 days detected by remote sensing and in-situ prior to the onset of CMEs and spacecraft observations. The present enhanced 2 days after the onset of study deals with the influence of four CMEs. The deviations in cosmic ray types of CMEs namely Asymmetric intensity are more pronounced in case 'Full' Halo CMEs, Partial Halo CMEs, for asymmetric and complex full halo Asymmetric and Complex 'Full' Halo CMEs compared to other CMEs. The CMEs and 'Full' Halo CMEs on cosmic cosmic ray intensity shows nearly good ray neutron monitor intensity. The anti-correlation with IMF strength (B) data of ground based neutron monitor during asymmetric full halo CMEs and of Moscow and CME events observed partial halo CMEs, whereas it shows with instruments onboard and Wind poor correlation with B during other spacecraft have been used in the CMEs. The IMF, B significantly present analysis. The method of decreased five days prior to the onset superposed epoch (Chree) analysis has of asymmetric and full halo CMEs and been used to the arrival times of these four days after the onset of partial halo CMEs. It is noteworthy that the CMEs, whereas IMF strength (B) frequency of occurrence of Asymmetric significantly enhanced 5-6 days prior 'Full' Halo CMEs is significantly high, and after the onset of asymmetric and whereas frequency of occurrence of complex full halo CMEs. IMF strength Asymmetric and Complex 'Full' Halo (B) significantly depressed 2 days prior CMEs is low compared to other CMEs. and 4 days after the onset of full halo Significant enhancement in cosmic ray CMEs. However, IMF, B significantly intensity is observed after 4 days of enhanced from its minimum to the onset of asymmetric full halo and 6 maximum values in 2 days interval days after the onset of full halo CMEs. prior to the onset of CMEs and in 3 The fluctuations in cosmic ray intensity days interval after the onset of CMEs. are more prior to the onset of both types of the CMEs. However, during Keywords : Coronal mass ejections, Partial Halo CMEs the cosmic ray interplanetary magnetic field, cosmic intensity peaks, 8- 9 days prior to the ray 2 Mishra et.al. Coronal mass ejections

occurrence rate at all, low, and high 1 Introduction latitudes, as well as the observed CME

Earlier, it was thought that parameters. solar flares were responsible for major interplanetary particle events and 2 Data and analysis geomagnetic storms. However, CME events observed by recently we have seen an important instruments onboard SOHO and Wind paradigm shift such that now coronal space craft for the period 2005-06 mass ejections (CMEs), not flares, are have been considered for the present considered the key causal link with work. We have analyzed sixty-seven solar activity. CMEs during 2005-06. The Bieber and Evenson (1998) temperature and pressure corrected noticed strong enhancements of the hourly data (counts of neutrons) of cosmic ray anisotropy before and cosmic ray intensity from Moscow during the January 1997 neutron super monitor 24NM-64 CME/magnetic cloud. From a multi- (Latitude 55.47 N, Longitude 37.32 E, station analysis of neutron monitor Altitude 200 m, Standard pressure data, they conclude that B×∇n drift is 1000 mb, Geomagnetic cut-off rigidity a primary source of CME-related 2.43 GV) have been used, where the anisotropies for 5 GeV cosmic rays. long-term change from the data has Evolution of the cosmic ray density and been removed by the method of trend density gradients is closely linked to correction. The days of Forbush magnetic properties of the ejecta, and decreases have also been removed provides information on the magnetic from the analysis to avoid their cloud and related features as they influence in cosmic ray variation. Chree approach and pass Earth. Strong analysis of superposed epoch has been enhancement of the field-aligned applied on the presure corrected daily anisotropy was observed primarily average cosmic ray intensity data with during the 9 hours prior to shock respect to full hallo CMEs, partial hallo arrival condition of Earth. Cane et al. CMEs, Asymmetric and Complex 'Full' (1996) reported a significant Halo CMEs and asymmetric hallo CMEs. relationship between CMEs and cosmic Statistical significance of the results so ray variations. obtained is evaluated by using a We present a study of the method suitable for Chree analysis. short-term evolution of coronal mass ejections observed by the Large Angle 3 Discussion and Spectrometric Coronograph Fig 1 shows the frequency of (LASCO) on board SOHO during 2005 occurrence of four different types of and their association with the CMEs identified during the period modulation of galactic cosmic ray 2005-06. It is clearly seen from the (GCR) intensity observed at 1 AU by figure that frequency of occurrence of the Moscow neutron monitor and IMP- Asymmetric 'Full' Halo CMEs is 8 spacecraft. We compare the short- significantly high, whereas frequency term GCR modulation with the CME of occurrence of Asymmetric and PROCEEDINGS OF THE 31 ST ICRC, LODZ 2009 3

Complex 'Full' Halo CMEs is low Asymmetric and Complex 'Full' Halo CMEs compared to other CMEs identified 2 during the period of investigation. It is 1.5 also noticed that frequency of 1 occurrence of full halo and partial halo 0.5 0 CMEs is almost equal. -10-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 -0.5 NM Count NM (%) Full hallo CMEs -1 30 25 -1.5 20 -2 15

10 -2.5 5 Days Asymmetric full hallo CMEs 0 Partial hallo CMEs Partial Halo CMEs

0.8

0.6

0.4 Asymmetric and complex full halo CMEs 0.2

0 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 -0.2 NM Count(%) NM -0.4

Fig 1: Frequency of occurrence of (1) -0.6

Asymmetric 'Full' Halo CMEs, (2) Partial -0.8

Halo CMEs (3) Asymmetric and -1 Complex 'Full' Halo CMEs and (4) 'Full' Days Halo CMEs during 2005. 'Full' Halo CMEs 1.2 1

To study the effect of these 0.8 CMEs on cosmic ray intensity, we have 0.6 adopted the Chree analysis of 0.4 0.2 superposed epoch for days – 10 to + 0 NM CountNM (%) -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 10 and plotted in Fig 2 (a, b, c, d) as a -0.2 percent deviation of cosmic ray -0.4 intensity data of Moscow neutron -0.6 -0.8 super monitor for 2005-06. Days Asymmetric 'Full' Halo CMEs Fig 2: The results of Chree analysis of 1.5 superposed epoch from –10 to +10

1 days with respect to zero epoch days as a percent deviation of cosmic ray 0.5 intensity for (a) Asymmetric 'Full' Halo CMEs, (b) Partial Halo CMEs, (c) 0 -10-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 Asymmetric and Complex 'Full' Halo Moscow NM CountNM(%) Moscow

-0.5 CMEs and (d) 'Full' Halo CMEs. Significant enhancement in -1 cosmic ray intensity is evident after 4 Days days of the onset of asymmetric full halo and 6 days after the onset of full

halo CMEs. The fluctuations in cosmic 4 Mishra et.al. Coronal mass ejections ray intensity are more prior to the correlation coefficient (r) to find out onset of both types of the CMEs. the possible correlation between these However, in case of Partial Halo CMEs parameters during the onset of four the cosmic ray intensity peaks, 8- 9 different types of CMEs. The days prior to the onset of CMEs and correlation coefficient between these depressed 3 days prior to the onset of two parameters is also calculated. As CMEs. In case of asymmetric and depicted in the plots and observed complex full CMEs, the intensity of correlation coefficient, the cosmic ray cosmic rays depressed 2 days prior to intensity shows nearly good anti- the onset of CMEs and enhanced 2 correlation with IMF strength (B) days after the onset of CMEs. Thus, we during asymmetric full halo CMEs (r = may conclude that all the four types of - 0.44) and partial halo CMEs (r = - CMEs studied here produced significant 0.46), whereas a poor correlation is disturbances in cosmic ray intensity. seen between these two during However, the deviations in cosmic ray asymmetric and complex full halo intensity are more pronounced in case CMEs (r = - 0.14) and full halo CMEs (r for asymmetric and complex full halo = 0.24). CMEs. Further to investigate the effect 5 Conclusions of these CMEs on interplanetary Thus, we can say that CMEs magnetic field (IMF) strength B, we are more effective transient have applied the Chree analysis of modulators of cosmic ray intensity. superposed epoch for days – 10 to + However, study of the simultaneous 10 and plotted (Figs. Not shown here) deviations in solar wind plasma field as a percent deviation of IMF, B data parameters during the passage of for 2005-06. these CMEs, their transit speed, It is quite observed that IMF magnetic field enhancements etc. are strength (B) significantly enhanced 5-6 needs to be studied in more detail for days prior and after the onset of establishment a better model. asymmetric and complex full halo CMEs. 6 References Here it is noteworthy that IMF [I] Bieber, J. W., Evenson, Paul, strength (B) significantly depressed 2 1998. CME geometry in relation days prior and 4 days after the onset to cosmic ray anisotropy. of full halo CMEs. However, IMF, B Geophysical Research Letters 25 significantly enhanced from its (15), 2955-2958. minimum to maximum values in 2 days [II] Cane, H. V., Richardson, I.G., interval prior to the onset of CMEs and Von Rosenvinge, T.T., 1996. in 3 days interval after the onset of Cosmic ray decreases 1964- CMEs. 1994. Journal of Geophysical We have also plotted the Research. 101, 21561-21565. scattered diagram (not shown here) between cosmic ray intensity and IMF strength (B) along with regression line,