Kaushik, Subhash C

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Indian J . Phys. 75B(2). 133-135 (2001)U P  Ban in tanu tiona l jou rna lInfluence of magnetic field of solar plasma on galactic cosmic raysSubhash C KaushikD epartm ent o f  Physka, O ovem m ent Autonom ous P G College. Sidhi-486 661. M adhya Pradesh. India E -m ail . subaBh-KaUBhik@irediffmail.comRBceiv^d 2 December 1998, accepted 9 February 200JA b s tra c t  : T w o types o f  interplanetary disturheiiceB nam ely, m agnetic clouds events (M C E 's) and bi-directional events (B D E 's) are taken  to  study the short-term  changes in  so la r w ind p lasm a com ponents as well as in cosm ic ray  intensity. These tw o types o f  d isturbances are again  separated into tw o  oategories : (i) coronal hole associated events (M C E ’s and B D E 's), and (ii) without coronal hole associated events (M C E ’s u id  BD E ’s). C oronal ho le  associated B D E ’s are found signifioantly responsible for enhanced plasm a velocity. Both disturbances in  either the  category, produce short-term  decrease in  cosm ic ray  intensity.K ey w o rd s  . In terp lanetary  disturbances, cosm ic rays, so lar wind param eters.PA CS N os. . 96 .60 .V g. 96 .60 .R dInterplanetary disturbances with a shock wave at 1 AU are classified into two categories; first in which the shock wave IS accompanied by a magnetic cloud known as magnetic cloud event (MCE), the second type of event where the shock wave is followed by a plasma region with bi-directional solar wind electron heat flux (BEHF) is termed as bi­directional event (BDE). It has been found that the plasma and magnetic field characteristics of these two types of tnuisient disturbances are distinguished markedly. If magnetic cloud and BEHF are truly fast magnetized plasmoids moving away from the Sun into interplanetary qrace, then the interplanetary magnetic field must be draping around them[1]. This field line drawing around BEHF is treated as a likely source of the out-of>tbe ecliptic magnetic fields at 1 AU[2,3]. IMF draping was thought of as being the possible cause of the characteristic eastward deflection of BEHF at the Earth’s orbit. This provides insight into the physical nature of these two inteiplanctary transients.In this paper, a systematic study has been performed to draw the relationship of magnetic field characteristics of MCE and BDE with various inleiplanetaiy/geomagiietic phenomena as well as with cosmic ray intensity. MCE and BDE events data with an accuracy (tfl hour from the period 197K-1982 are taken from IMP 8 and l ^ E  3 obsnvations K). The shock wave in the solar wind is generally ideonified >n high time resolution plots of-solar wind plasma andmagnetic field data as abrupt and simultaneous increases in bulk flow speed V, particle density Np, proton temperature Tp and magnetic field B [3], Solar wind components values are taken from inteiplanetary medium data book |6]. For cosmic rays, we have taken the daify mean tenqienituie and pressure corrected values recorded by super neutron momtor at Calgary (lat. 51.05° N, long. 114.08° W, cut-off tigidily 1.09 GV). We have applied super posed epoch anatysis to find short-term effects.It is established that magnetic clouds events (MCE’s) and bi-directional events (BDE’s) consist of different plasma and magnetic field characteristics. Such disturbances in interplanetary medium certainly produce influences on energetic particles of galactic cosmic rays as well as the disturbances in Earth’s magnetic field. Coronal holes are the regions on the outer surfoce of the Sun, propagating high­speed solar wind stream into inteiplanetaiy medium. We have divided both MCE and BDE into two classes: one that is associated with coronal holes and another, wtuch are not associated with coronal holes and then explicitly analyzing their influences.Figure 1 shows the results of Chiee analysis (rfBDE and MCE events with solar wind components, such as bulk flow speed, ion density and proton temperature on left and right panels respectively. These two events are associated. w*UilACS134 Subhash C Kaushikcoronal holes. Zero days on the time scale corresponds to the beginning of the event. Coronal holes associated BDE’s show significant increase in solar wind velocity and proton temperature.BDE MCEFigure 1. Superposed epoch analysis o f  the plasma parameters i.e solar wind velocity V (km s~'), ion density Np (cm~^), proton temperature T pti\(P  (K") in transient disturbances o f two types ; B D E  (left) and M C E  (right). C lo n a l  holes— associated events.Both show transient enhancements lasting six to seven days after the zero days. Ion density decreases immediately after the occurrence of the event. However, on the other hand, results of Chree analysis of coronal hole associated MCE’s show different effects on solar wind velocity as shown in Figure I (right panel). An enhanced bulk solar wind velocity and ion density on the onset of the event day is evident. Proton temperature does not provide any meaningftil result except a sharp decrease on the first day after the event day. Hence, it is concluded that the bi­directional events (BDE’s) are more effective to produce increase in solar wind velocity as well as for transient fluctuations in ion temperature than the events of magnetic clouds (MCE’s).Further, we have performed the Chree analysis to observe the effect of BDE’s and MCE’s that are not associated with coronal holes. Results are shown in Figure 2. The BDE’s show a maximum solar wind speed on the event day, which starts increasing before 1 day of the event, goes to maximum, then decreases sharply taking 5 days on the time scale. Similarly, the ion density and temperature starts increasing before one day and after having the maximum values on the event day decrease continuously for the following next day. Similar results for solar wind velocity are observed for MCE’s without coronal hole associated events. However, density values are found minimum upto four days after the zero epoch day. Fluctuations are seen for the proton temperature. Here, we can conclude that only coronal hole associated magnetic cloud events are found responsible to produce significant decrease in the solar wind velocity on short-term basis.Figure 2. Superposed epoch analysis o f the plasma parameters i e. solar wind velocity V (km s~'), ion densit>’ Np (cm'^), proton temperature Tp X 10^  (K”) in transient disturbances o f two types ; B D E  (left) and MCE (right), these events are not associated with coronal holes.Figure 3 shows the effects of these two types of transient variations on cosmic ray intensity on short-term basis. SlightBDE MCEi"1 ' M apwn •m-iATM  mNH: / vM H O a io  iv iim'1  0 I  •  •  a to ^  t OAira. ................' i .......■MVIFigure 3. Superposed epoch analysis o f cosmic ray intensity associated with transient disturbances (BD E and M CE ). Left panel shows BDE associated with C H  (bottom) and without C H  (top). Right panel represents M C E  with C H  (bottom) and without coronal holes events (top)decreases are evident in the Chree analysis plots for both the categories of BDE’s and MCE’s. From critical examination, it can be said that the bi-directional events with or without coronal holes produce larger decrease in cosmic ray intensity than the magnetic cloud events. Hence, we can infer that coronal holes are not a prominent ftetor to produce decrease in cosmic ray intensity.On comparing averaged relationship of plasiha parameters for MCE and BDE from Figures I and 2, it is found that the characteristics of these two types of transient d istu rbances in association with coronal holes or without coronal holes association, differ appreciably in plasma velocity and temperature. An increase in the solar wind plasma velocity in the BDE with CH case is about 50% larger than those for MCE and CH case. MCE and BDE widiout CH only show slight differences in proton temperature where BDE without CH produce 40% large decrease in comparison to MCEIrfiuence of magnetic field of solar plasma on galactic cosmic rays 135without CH events. However, other investigators have reported different magnetic field characteristics in these two types of transient disturbances (BDE and MCE) [1]. The magnitude of the magnetic field in the sheath region in MCE increases as one approaches the MC boundary, while in BDE, immediately in front of BEHF boundary, the magnetic field decreases. Larger and varying magnetic field during the period of MCE’s, certainly produce decrease in solar wind plasma velocity as well as in the intensity of cosmic rays. Therefore, increase in plasma velocity is associated with bi­directional events accompanied with coronal holes.It may be concluded from the analysis that:1. Bi-directional events associated with coronal holes are found to be responsible for producing increase in solar wind plasma velocity on short-term basis.2. The magnetic cloud events do not produce any significant charge in i^ asma components.3. Both types of transient disturbances arc found responsible factors in producing decrease in cosmic ray intensity on short-term basis.AcknowledgmentsAuthor thanks the World Data Centre A (USA) for providing interplanetary medium data. This work is supported by University Grant Commission, CRO, Bhopal, under Grant No. 19-19/98 (CD-Il/CRO).Rcfercncct{!] V G Famshtein and A P Kaigorodov Flanei Space. Sci 44 387 (1996)[2] S C Kaushik and P K Shrivastava Imiian J Phys 74B 1 (2000)[3] J T Gosling and D J McComas Geophys Res Lett 14 14355 (1987)[4] D A Couzens and J H King Interplanetary Medium Data Book Supplement 3 N S S D C/W D C-A 86-04 (Nall Space Sci. Data Center, Grcenbelt, Maryland) (1986)[5] G Borrini, J T Gosling, S J Bame and W C Feldman J. Geophys. Res 87 4365 (1982)[6] J H King Interplanetary Medium Data Book-Supplement NSSDC/WDC-A (Natl Space Sci Data Center, Grcenbelt. Maryland) (1977)

Influence of Magnetic Field of Solar Plasma on Galactic Cosmic Rays

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/6250/1/Influence%20of%20Magnetic%20Field%20of%20Solar%20Plasma_Subhash%20C%20Kaushik.pdf

Influence of Magnetic Field of Solar Plasma on Galactic Cosmic Rays

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