GROUND LEVEL ENHANCEMENTSAND THEIR SOLAR FEATURES DURING SOLAR CYCLE 23 MAHEDRAPRATAPYADAV* *Govt.Tilak PG College, Katni, (M.P.), India ABSTRACT We study the observed properties of the ground level enhancement (GLE) and their associated phenomena namely coronal mass ejection (CMEs) and solar flares. Both above are the potential source of particle acceleration during solar cycle 23. The solar cycle 23 to be a great interest due to many peculiarities for the researchers. A study of the parameters of the sixteen GLEs recorded during the period 1996-2008 along with associated solar activity, including the main properties of CMEs, solar flares and the radio bursts has been analyzed and an attempt has been made to understand the connection of these events. The 80% of the CMES are full halos and three non halos having angular width in the range 167 to 212 degrees. In maximum number of studied cases seem to be connected with very intense flares of long duration, having a mean duration of 164.5 min and a mean importance value of X5.9 with mean linear velocity 1876 km/sec. of CMEs. An M7.1 flares and a 1200 km/sec CMEs are the weakest event of 16 GLEs. The GLE particle release is delayed with respect to the onset of all electromagnetic signature of the eruptions with a mean time delay of about 38 min. This result is very useful of their monitoring and prediction. The 86% GLEs are associated with H alpha solar flares directed towards west and 62.5% GLEs are associated with northern hemisphere of the disk. No H alpha solar flares have occurred beyond 40 0 helio latitude. KEYWORDS: Coronal mass ejections (CMEs), Ground level enhancements (GLEs), Solar flares, Solar energetic particles (SEPs). 1 INTRODUCTION Ground level enhancements (GLEs) of cosmic rays are solar energetic particle events (SEPEs) that can be recorded from ground based detectors as sharp increase of short duration in the cosmic ray (CR) intensity counting rates. These energetic particles recorded by the neutron monitors must have energies of at least 500 mev in order to access the Earth is magneto sphere and to be recorded at the ground as secondary cosmic rays Simpson (2000) 1. GLEs in solar energetic particle (SEP) events provide the opportunity to detect energized 218
coromalmatrial from the Sun that reaches Earh s atmosphere with in a matter of ~ 10 minutes, Understanding of GLEs is an important for identifying the acceleration mechanism of the lower SEPs. In addition to the interesting physics of particle acceleration, SEPs and GLE events may lead to important changes in the Earth s polar atmosphere via enhanced ionization (Usokin et al., 2011) 2. The spatial and temporal information on the release of GLE particles provides important details that may distinguish between the two particles acceleration mechanisms (shocks and flares reconnection) that operate at distinct spatial locations in solar transients. Major solar transients are accompanied by solar flares to be due to electrons accelerated in the energy release region that flow towards the sun and produce enhanced electromagnetic emission in X ray, H alpha, microwave and coronal mass ejections (CMEs) driving magneto hydrodynamic (MHD) shocks that also accelerate electrons to produce type II radio bursts. Shock and flare reconnection process can also accelerate protons to high energies. Impulsive SEP events without accompanying shocks and energetic storms particle events detected by space craft near earth are concentrate proofs for the reality of flares and shocks acceleration processes. Traditionally flares are thought to be responsible for GLEs but the importance of CMEs is recognized much later Kahler et al.(1978) 3. Recent publication on the production of energetic particles by the Sun can be found in Lopate (2006) 4 ; Cliver (2009) 5 ; Kudela (2009) 6 ; Belov et al. (2010) 7 and others. The acceleration mechanisms that takes place during GLE events have not been fully understood till today. It is known that proton acceleration could take place either in process involving magnetic reconnection Cane et al.,(2006) 8 or at Coronal or CMEs driven shocksreames(1999) 9. Recent studies suggest that there might be a strong possibility that CMEs and solar flares are manifestations of the same transients process Lin et at.(2005) 10. Due to the fact that these relatively rare events are very important for space weather studies. Mavromichalaki et al.(2007) 11 CMEs are reported for only a handful GLE prior to solar cycle23cliver(2006). 12 Kahler (1994) 13 ; Bieber et al. (2002, 2004, 2005, 2008) 14,15,16,17 ; Grechnev et al. (2008) 18 and Tylka et al. (2010) 19 have been perform several studies on individual GLE events for solar cycle 23. Kahler et al. (2003) 20 and Gopalswamy et al. (2005, 2010a) 21,22 have been performed preliminary statistical studies involving CMEs are reported in the recent past. Recently, a number of studies regarding the study of the main properties of many events have been presented for those occurring during 23 solar cycle. (Storini et al. 2005) 23 ; Andriopoulou et al. (2010) 24 ; Belov et al. (2010) 25 ; Feroz et al. (2010) 26 ; Gopalswami et al. (2010a) 22 ) 219
How solar energetic particle are accelerated to Gev energies, when and at what height in the Corona they are released are important questions that have not been fully answered yet now. More work should be needed in this direction. 2 Data Source In our analysis, cosmic ray intensity ground based data from neutron monitors stations representing to the world wide network (http://www.nmdb.eu/) are used. For related solar phenomena, we have used data for the coronal mass ejections from the Solar Helioobservatory (SOHO) Large Angle Spectrometric Coronagraph (LASCO) catalogue (http://cdaw.gsfc.nasa.gov/cme list/). We have used H alpha and X ray solar flares from the GOES satellites and collected from the NOAA database (ftp://ftp.ngdc.noaa.gov/stp/solar_data/solar_flares) and are also used finally. The radio signatures of the solar phenomena are taken into account by using data from NOAA data base and ARTEMIS, IV radio spectrometer (http://www.cc.uoa.gr/~artemis/artemis 4_list html). Each event is separately observed and time relationship among the GLE events and various solar phenomena are carefully examined. In addition to above, we have also examined to various parameter of solar flare, radio bursts and CMEs in relation with GLEs. 3 Results and Discussion We have observed 16 GLEs during 23 solar cycle. GLE onset times have been determine as the time when the instaneous cosmic ray intensity starts systematically exceeding the level of 2% increase compare to the 2 hour pre increase base line. Slightly different criteria is used by Gopalswamy et al. (2010a) 22 when onset time correspond to the time when the GLE intensity reaches ~ 10% of the peak intensity. We have also define the inferred onset times derived assuming a path length of 1.2 Astronomical unit and the particle kinetic energy to be ~ 1 Gev. We are wanted in comparing the GLE onsets with those of soft X ray flares, White light CMEs and radio bursts, we need to take into account of the travel times of electromagnetic waves form the Sun to Earth, which is 8.3 minute. Instead of converting the EM signal onsets at 1AU to the corresponding onsets near the sun, we give the GLE on sets with reference the arrival time of EM signals at the Earth by subtracting the time taking by the GLE particle of corresponding event on set at Earth and adding 8.3 Min. For example 6 Nov 1997 event, the onset time is determine to be 12.10 UT. The speed of 1 Gev 220
particles is ~ 2.63 x 10 5 km/sec, so it takes 11.4 min for the GLEprotons to reach earth atmosphere. Thus the inferred on set times (Solar particle release times) (SPR) are ~ 3 minute earlier than the Earth on set times. It is also remarkable that the solar particle release time can be substantially different in the path length differs from 1.2 AU, For example, it path length is 1.5 AU, the SPR is ~ 6 minutes earlier than the Earth on set time. In order to define the parameters of GLE (Onset, peak time and intensity), we have used 5 minute data from high latitude neutron monitor with stable operation South pole, Oulu, Kiel, Mcmurdo, Apatily, Cape Schmidt, Goosebay, LARC, Mawson). In most cases, timing of GLE as inferred from different station agrees with each other with in 5 minutes (Reams, (2009a) 27 ;Andriopoulou et al. (2011) 24 ). However, the GLEs with complex structure containing distinct prompts anisotropic and gradual delayed components (Moraland Mccracken, 2011) 28, the timing may be quite uncertain as manifested in a range of the values. For examples 29 Oct 2003 and 20 Jan 2005 GLE events. In such cases, we have used the prompt component timing for analysis. In contrast to the agreement of timing, the intensity of individual GLE varies quite a bit as recorded by different stations. For consistency, we use here intensities from the Oulu whose data are available for all the analyzed GLE events. In the cases with a large difference between Oulu and other stations likely South pole or Mc-Murdo, we show in parentheses the maximum peak increase in cosmic ray intensity. We have also examined SEP in the >10 Mev energy channel as detected by GEOS satellite in particle flux unit (Pfu) with 1 pfu = 1 particle cm -2 s -1 Sr -1. The SEP intensity is the peak value before the shock peak the so called energetic particle event which have been observed each GLE event. The metric (m) type II onset times are generally the earliest onset in the on line catalog available from the National Geophysical Data Center (NGDC ftp://ftp.ngdc.noaa.gov/stp/solar data/solar radio/spectral/typeii 1994-2009). The starting frequencies are given in the catalog range from 80 ± 430 MHz. In addition to the NGDC list, we also examined the actual dynamic spectra from individual observatory websites (culgoora, Hiraiso, IZMIRAN; Nancay) and the Radio solar Telescope Network (RSTN) dynamic spectra made available on line. In all cases, we are able to check the dynamic spectra and hence verify the starting times of metric type IIburstin a few minutes. We observed that the dynamic spectra are very complex in the metric domain, with intense type III and type IV burst accompanying the type II burst. The leading edge of the metric type IV burst some time is superposed with a drifting feature similar to the type IIburst. In some events, the occurrence of a type II burst at 14 MHz in the Wind/WAVES dynamic spectrum is useful in delineating the metric type II burst as the higher frequency 221
extension. For example GLE of 2 May 1998 event, there is no type II burst. However, there is clear type II burst at the leading edge of the IV in the decameter-hectometric (DH) spectral range extending from 14 MHz down 7 MHz. Fortunately, the decametric array at Nancy observed this event. It is notice that we are mainly concerned with the onset time of the type II burts rather than the starting frequency. We expect some difference in location of the plasma levels on different days, but we cannot infer this location from the type II data because of the uncertainty in the starting frequency and the lack of information on the mode emission for some events. Nevertheless the range of frequencies over which the type II burst are reported to occur in narrow enough that we compute the height of the CME at the time of the metric type II burts as the heliocentric distance at which the shock forms or the shock is capable of accelerating electrons in sufficient numbers to produce the observed type II burst (Gopalswamy et al, 2009) 29. The association of GLE events with soft X-ray flares has been studied during the 23 solar cycle. The onset times reported in the Solar Geophysical Data (SGD) have been carefully examined. The correct identification of flares times is important for the timing studies of GLES, using the soft X ray observations avoids data gaps in the H- alpha coverage and the variation from observatory to observatory in estimating the flare size. The flare onset times used by Gopalswamy et al. (2010a) 22 are mostly based on SGD. Since the active regions in which the GLEs occurred are prolific producers of flare and CMEs (Goplaswamy at al., 2004) 30, the flare onsets have to be carefully examined to separate the preceding events from the GLE associated flares. For example, 28 Oct 2003 GLE event is preceded by a fast CME speed ~ 1000 km/sec from the same sources region within 40 min (Gopalswamy et al. 2005) 21. The SGD flare onset time is 09:51 UT which actually corresponds to the onset of the preceding flare associated with the 1000km/sec. Flare times are fairly accurate for all the events, except for the 18 April 2001 GLE events because it occurred behind the limb. Nearly half of the GLE associated flares showed complex GOES soft X ray light curves indicative of preceding activity. All GLEs of 23 solar cycle are found to be associated with CMEs where white light corona-graphic observations are available. For the 24 Aug 1998 GLE event, there is no CME observation near the sun because SOHO is temporarily disabled during June 1998 to Oct 1998. However, there is ample evidence for the CME associations of the 24 Aug 1998 GLE event based on interplanetary CME (ICME) observations. The GLE intensity measured at Olu NM varies over two orders of magnitude minimum 3% to maximum 277%. The median intensity if only 11% and the larger mean value 34% because of the three large events in the tail of the distribution. The intensity varies 222
of the three orders of magnitude when all the NM stations are considered but the rigidity cut off is not the same at various NM stations. It is observed that GLEs are associated with major flares and CMEs of very high speed source regions of GLE on the sun. All the GLEs of 23 solar cycleoriginated from numbered active region. There are 11 active regions that produced the all GLEs events. The Four active regions produced multiple GLE events. AR10486 produced 3 consecutive GLE events namely 28 Oct 2003, 29 Oct 2003, 2 Nov 2003 whereas AR 8210 produces the two consecutive GLE events (2 May 1998, 6 May 1998). The AR0720 produced two GLE events 17 Jan 2005, 20 Jan 2005 while AR 9415 resulted in GLE 15 April 2001, 18 April 2001 events. Statistically, it is observed that five GLE are associated with 2B importance of H alpha solar flare where as five GLE are associated with 3B importance of Hα solar flares. Two GLE events are associated with 4B importance of H alpha solar flares. Out of three GLE events, One GLE events is associated with 1B importance, other event is associated with 1N where as other one is associated with 1F importance of H alpha solar flares. Observing the position of flares on the solar disk, it is found that thirteen of them have a west origination where as two events are east origination. This result is consistent with Duldig et al. (1993) 31. This result shows that there is a strong tendency for solar active regions responsible for GLE to be located at west ward solar longitudes. It is also observed that 10 events are associated with solar flare directed towards Northern hemisphere whereas 06 events are associated with southern directed the H alpha solar flares. No, Hα solar flares have occurred beyond 40 degree of heliolatitude. This result shows that solar flares of low latitude are capable of producing a strong tendency for solar active regions which are responsible for generation of GLEs. The X ray flare classification have been observed during 23 rd solar cycle. It is found that maximum number of X ray solar flares are very intense, having a mean importance value of X5.9 class which is much larger in comparison to the mean flare value of the complete solar cycle that is C1.6. This result is agrees with Gopalswami et al. (2010a) result. The flare which is associated with 18 April 2001 event is excluded from this analysis because it is estimated that this event have occurred behind the west limb and therefore it is almost entirely occulted. The radio emission of type II, III and IV type radio bursts have been studied related to GLE during the 23 rd solar cycle. Observing the data of the related radio bursts, it is concluded that for all the observed GLEs of study cycle 23 there is always strong radio emission of II, III and IV radio bursts related to each event. Only in the case of 18 April 2001 event, there is an 223
absence of the type IV radio burst but this could be attributed to the fact that its related flare behind the limb. It is found that the CMEs are related to GLEs are halo or partial halo and fast events. This is also agree with the result obtained by Andriopoulou et al. (2011) 24. It is also observed the fact that solar flares and CMEs started almost simultaneously in the majority of GLEs together with the fact that there is a time relationship between the intensity of flare and velocity of CMEs, which provides additional evidence that flares and CMEs could be manifestations of the same eruptive process, at least for GLE related events. It is also observable from fig 1,2 that the number of GLE does not follow the solar cycle but steadily increases from minimum to the declining phase. It is observed that 56.25%, 31.25%. GLEs are associated with velocity range, 1000-2000 km/sec, 2000-3000 km/sec respectively where as 6.25% GLEs are associated with each velocity range 0-1000 km/sec. and 3000-4000 km/sec during the 23 rd solar cycle as shown in figure 3. Fig.1 shows the variation of sun spot numbers (SSNs) during the years 1996 to 2007. Fig.2 shows the variation of GLEs during the year 1996 to 2007. 224
Fig.3. Shows that the occurrence of GLEs with their velocity range during the year 1996-2006. 4 Conclusions The GLE events of cycle 23 have been analyzed the most significant conclusions that come up from this analyzed including all events of solar cycle 23 are the following. (i) There are 16 GLE events in 23 solar cycles and are rare events with an occurrence rate of ~ 1.5 per year. (ii) The number of GLEs does not follow the solar cycle, but steadily increases from the minimum to the declining phase. (iii) The GLEs mostly arise from super active regions that produce many CMEs in quick succession. (iv) 62.5 GLEs are associated with H alpha solar flare directed towards southern hemisphere whereas 37.5 are associated with northern hemisphere of solar disk. (v) 86% GLEs are associated with H alpha solar flares directed towards west ward longitude of hemisphere of solar disk. (vi) The more than 56% GLEs are associated with velocity range 1000-2000 km /sec where as 31% are associated with 2000-3000 km/sec which shows that GLE associated CMEs are the fastest. (vii) Each GLE to be associated with very intense solar activity. It seems that there are an always an intense flares, a fast CMEs and strong radio emission of radio burst type II, III and IV related to the event. (viii) Observation shows that the solar eruption associated with GLEs occur from near the disk center to locations well beyond the west limb. (xi) No, Hα solar flares have occurred beyond 40 0 helio latitude. It is observed that X5.9 is the mean importance of X-ray solar flare during 23 rd solar cycle associated with GLEs. 225
Acknowledgements We are thankful to various experimental groups for providing the data. In particulars, neutron monitors and solar observatories that kindly provided us with the data used in this work. References 1. Simpson J A, Space Sci. Rev., 93, 11, 2000. 2. Usoskirn I G et al, Atmos. Chem. Phys., 11, 1979, 2011. 3. Kahler S W et al., Sol. Phys., 57, 429, 1978. 4. Lopate C, American Geophysical Union, 283, 2006. 5. Cliver E.W., International Astronomical Union, 401, 2009. 6. Kudela K, ActaPhysicaSlovaca, 59, 537, 2009. 7. Belov AV et al,geomagnetism and Aeronomy, 50 (1), 21, 2010. 8. Cane HV et al, J. Geophys. Res., 111, A6, 2006. 9. Reams D V, Space Sci. Rev., 90, 413, 1999. 10. Lin J. et al. Astrophys. J., 1251, 622, 2005. 11. Mavromichalaki H et al., IEEETNS, 54, 1083, 2007. 12. Cliver EW, Astrophys. J., 639, 1206, 2006. 13. Kahler SW, Astrophys. J., 428, 837, 1994. 14. Bieber J W et al., Astrophys, J., 567, 622, 2002. 15. Bieber J W et al., Astrophys, J., 601, L 101, 2004. 16. Bieber J W et al., Geophys. Res. Lett.,doi : 101029/2004 GL 021492, 2005. 17. Bieber J W et al., In Pro. 30 th Int. Cosmic ray confmaxico City, 1, 229, 2008. 18. GrechnevVV et al., Sol. Phys., 252, 149, 2008. 19. Tylka AJ and Dietrich WF, Astronomical society of the Pacific, San Francisco, 329, 2010. 20. Kahler SW et al, In Pro. of the 28 th I.C.R.C., Tsukuba, Japan, 3415, 2003. 21. Gopalswamy N et al., In Pro. 29 th ICRC, Mumbai, 1, 169, 2005. 22. Gopalswamy N et al., Indian J. Radio and Space Phys., 39, 240, 2010 a. 23. Storini M et al., Adv. Space Res., 35, 416, 2005. 24. Andriopoulu M et al., Solar Phys., 269, 155, 2011. 25. Belov A. et al., Geomagn. Aeronomy, 50, 21, 2010. 26. Firoz KA et al., J. Geophys. Res., 115, A9105, 2010. 27. Reams D V, Astrophys. J., 693, 812 2009. 28. H. Moral and McCracken, Space Sci, Rev.,doi ; 101007/S 11214-011-9742-7 2011. 29. N Gopalswamy et al. Sol. Phys., 259, 227, 2009. 30. N Gopalswamy et al., J. Geophys. Res.,doi: 10,1029-JA 010602, 2004. 31. M. L. Duldig et al., In ProcAstrom.Soc. Australia, 10, 211, 1993. 226