OBSERVATION OF GROUND-LEVEL ENHANCEMENTS. Rogelio A. Caballero López Geophysics Institute, UNAM

Transcription

1 OBSERVATION OF GROUND-LEVEL ENHANCEMENTS Rogelio A. Caballero López Geophysics Institute, UNAM ISEST, 10/29/2015

2 Outline Solar Energetic Particles (SEPs) and Ground Level Enhancements (GLEs) GLE General Description Observations - High-Energy GLEs - Pulse shape - Anisotropy - Rigidity dependence Solar Cosmic-Ray (SCR) Spectrum from GLE Analysis Summary

3 SEPs and GLEs SEPs are detected by space missions (E from 0.1 to MeV) Impulsive and gradual events (Reames, 1999; Mewaldt et al., 2007) Impulsive: - Short-lived, heavier elements and higher ionization states better representative of the composition of source material from the lower corona Gradual: - Long-lived, lighter composition and less ionized characteristic of the composition of the solar wind or interplanetary medium Hence: Impulsive SEP events contain particles that were accelerated in the corona, with solar flares the primary candidates Gradual SEP events originate more likely due to acceleration in the bow shocks of Coronal Mass Ejections (CMEs)

4 Pulse Shape: Gradual vs Impulsive SEPs (Reames, 1999) Particles/(cm 2 sr s MeV) ISEE 3 (a) Gradual "Proton" Event (b) Impulsive " 3He-rich" Events MeV Electron 1-4 Proton 7-13 Proton Proton Dec Aug

5 SEPs and GLEs GLEs are caused by the high-energy end of the SEP spectrum (E 500 MeV), representing the strongest acceleration episodes on the sun GLEs are primarly detected by Neutron Monitors (NMs) composition and ionization state are lost However, NMs are sensitive to arrival direction indication for anisotropy GLE Clasification (Vashenyuk et al., 2011; McCracken et al., 2012; Aschwanden, 2012; Gopalswamy et al., 2012): - High Energy Impulsive (HEI) GLE or Prompt Component (PC) Highly anisotropy, exponential spectrum exp [ E/Eo] Accelerated in electric fields associated with magnetic reconnection in the corona - Gradual GLE or Delayed Component (DC) Mildly anisotropy, power-law spectrum E γ due to stochastic acceleration in turbulent solar plasma in the outward expanding CME

6 Proton fluence spectra for GLEs 67 to 70 (Mewaldt et al., 2012) NMs 16 GLE Events in Solar Cycle 23, γ Large, Non-GLE Events in Solar Cycle 23, γ Break Energies from 2 to 46 MeV (see Schwadron et al., 2015)

7 GLE General Description Increase in the counting rate of the detector at the Earth surface Counts from SCRs are superposed on the background rate due to galactic cosmic rays The fractional increase (%) is defined as: δn Ng 100 (N g + Ns) Ng Ng 100 = N solar N galactic 100

8 GLE General Description Its magnitude depends on the: - Position of the particle source on the solar disk Preferentially from West solar hemisphere - Solar cosmic-ray spectrum at the top of the Earth atmosphere (Proton Energy > 500 MeV or Rigidity( pc/q) > 1 GV) - Asymptotic cone of viewing of the detector Angle between arrival and viewing directions - Geomagnetic Cutoff Rigidity Higher increases for polar detectors - Altitude above sea level Absortion mean free path for solar particles shorter than for galactic Higher increases for mountain detectors - Detector response function Higher increases for detectors more sensitive to low-energy CRs

9 GLE General Description Response (left) and Fractional Increases (right) (Caballero-Lopez and Moraal, 2012) Galactic CRs Solar CRs g/cm 2 Differential Response Functions, (%/GV) qa>0 IceTop 9,300 ft qa<0 qa>0 qa<0 NM Sea Level MT 720 ft Rigidity (GV) NM 30,000 ft Fractional Increases [δn/n=n s /N g ] Differential Counting Rate and Response, (%/GV) Sea Level (1033 g/cm 2 ) Response Differential Counting Rate P -6 P -5 P -4 P -4 P -5 P -6 Galactic Solar Max Rigidity (GV)

10 Observations 71 GLEs have been observed since 1942 ( 1/year) Mostly with Neutron Monitors GLE Database is available at: (Acknowledgments: M. Shea, D. Smart, M. L. Duldig, E. A. Eroshenko, and H. Moraal)

11 HE GLEs > 10 % (McCracken et al., 2012): 44 events Sorted by Date (dd/mm/yy) Sorted by Size Sorted by Longitude GLE# Incr% Date Lat N Long W GLE# Incr% Date Lat N Long W GLE# Incr% Date Lat N Long W /02/ /01/ /01/ /07/ /02/ /02/84? /05/ /09/ /09/ /11/ /05/ /09/ /11/ /04/ /09/ /07/ /05/ /01/ /01/ /10/ /04/ /11/ /11/ /05/ /02/ /11/ /05/ /01/ /12/ /11/ /01/ /02/84? /12/ /09/ /10/ /02/ /08/ /10/ /08/ /08/ /07/ /04/ /04/ /08/ /05/ /09/ /06/ /06/ /11/ /11/ /05/ /05/ /12/ /11/ /09/ /05/ /07/ /08/ /10/ /11/ /10/ /01/ /01/ /12/ /01/ /10/ /02/84? /11/ /12/ /08/ /02/ /09/ /09/ /10/ /01/ /10/ /11/ /04/ /10/ /01/ /11/ /10/ /04/ /11/ /11/ /08/ /08/ /05/ /05/ /02/ /05/ /05/ /08/ /06/ /10/ /05/ /06/ /12/ /10/ /11/ /09/ /07/ /07/ /07/ /11/ /04/ /11/ /12/ /04/ /08/ /06/ /12/ /07/ /11/ /10/ /04/ /10/ /10/ /09/ /07/ /11/ /09/ /10/ /01/ /11/ /08/ /12/ /06/ /10/ /05/ /08/ /10/

12 Pulse Shape: GLE 42 vs GLE 69 GLE 42, 29 September 1989: third largest GLE, best example of a gradual event Originated behind western limb, only particles accelerated on an extended CME shock front could have reached Earth GLE 69, 20 January 2005: first (or second) largest GLE, best example of a prompt event (HEI) Perfectly connected to Earth, so first stage was dominated by flare acceleration

13 GLE 42 vs GLE 69 (Moraal and Caballero-Lopez, 2014) % Increase 100 GLE on 29 September 1989 (blue) GLE on 20 January 2005 (red) Apatity (<1 GV) Barentzburg (<1 GV) Cape Schmidt (<1 GV) Fort Smith (<1 GV) Inuvik (<1 GV) Mawson (<1 GV) McMurdo (<1 GV) Nain (<1 GV) Norilsk (<1 GV) Oulu (<1 GV) Thule (<1 GV) Tixie Bay (<1 GV) Sanae (1.06 GV) Goose Bay (<1 GV) Mirny (<1 GV) Deep River (1.02 GV) Ottawa (1.08 GV) Terre Adelie (<1 GV) South Pole (<1 GV) Sanae (1.06 GV) Calgary (1.08 GV) :00 02:00 04:00 06:00 08:00 10:00 12:00 Time (hr:min) from onset of event

14 Some GLE Remarks Large GLEs (>100%) originating at 24 West on the solar disk invariably commence with an HEI GLE: pulse duration 20 min. (from rise to 50% fall-off) (McCracken et al., 2012) Available acceleration mechanisms could explain some of the GLE characteristics: - Impulsive Event: Magnetic reconnection in the coronal material (from flares): shorter timescales and highly anisotropy - Gradual Event: Shock acceleration in front of the CME (cuasiparallel shock) or at the flanks (cuasi-perpendicular shock): longer timescales and less anisotropy For impulsive events, release of GLE particles during the flare hard X-ray phase, the acceleration occurs at height 1.05R s (Aschwanden, 2012) Release of GLE particles occurs when the CMEs reach an average height 3R s for well-connected events, and 5R s for poor-connected ones (Gopalswamy et al., 2012)

15 1000 GLE 42 (Moraal and Caballero-Lopez, 2014) GLE 42 on 29 September Stations Blue: Pc < 1.24 GV Neutron monitors Red: Pc > 1.24 GV Neutron monitors Green: Muon telescopes % Increase :00 13:00 15:00 17:00 19:00 21:00 23:00 Time (hr:min)

16 % Increase Anisotropy GLE 42 GLE 42 on 29 September 1989 < 1.24 GV Neutron Monitors Apatity (<1 GV) Cape Schmidt (<1 GV) Goose Bay (<1 GV) Inuvik (<1 GV) Mawson (<1 GV) McMurdo (<1 GV) Mirny (<1 GV) Oulu (<1 GV) South Pole (<1 GV) Terre Adeli (<1 GV) Thule (<1 GV) Tixie Bay (<1 GV) Deep River (1.02 GV) Sanae NM (1.06 GV) Sanae WM (1.06 GV) Calgary (1.08 GV) Ottawa (1.08 GV) Kergeulen (1.19 GV) Mt Washington (1.24 GV) 10 11:00 13:00 15:00 17:00 19:00 21:00 23:00 Time (hr:min) 90 Th Th Stations: < 1GV In CS 60 Ca In 30 CS Latitude ( o ) Ca Ma Ma Mi Mi Longitude ( o )

17 Anisotropy GLE GLE 42 on 29 September 1989 Ratio Thule/Mawson Ratio :15 (prompt peak) 13:45 16:40 18:00 (delayed peak) (anisotropy (decay variabilty small) stops) 1 12:20 14:40 16:10 17:00 18:00 19:40 22: :00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 00:00 Time (hr:min) 90 Th Th Stations: < 1GV In CS 60 Ca In 30 CS Latitude ( o ) Ca Ma Ma Mi Mi Longitude ( o )

18 % Increase GLE 42 on 29 September 1989 > 1.24 GV Neutron Monitors Rigidity Dependence GLE 42 Durham (1.41 GV) Hobart (1.88 GV) Mt Wellington (1.89 GV) Newark (1.97 GV) Magadan (2.09 GV) Kiel (2.29 GV) Moscow (2.46 GV) Novosibirsk (2.91 GV) Climax (3.03 GV) Dourbes (3.24 GV) Kiev (3.62 GV) Irkutsk (3.66 GV) Lomnicky Stit (4 GV) Jungfraujoch IGY (4.48 GV) Jungfraujoch NM64 (4.48 GV) Bern (4.49 GV) Hermanus (4.9 GV) Rome (6.32 GV) Alma Ata A (6.66 GV) Alma Ata B (6.69 GV) Tbilisi (6.91 GV) Potchefstroom (7.3 GV) Samarkand (7.65 GV) Mexico City (8.15 GV) Tsumeb (9.29 GV) Mt Norikura (11.39 GV) Tokyo-Itabashi (11.61 GV) Darwin (14.19 GV) % Increase 100 Goose Bay MT (<1 GV) Inuvik MT (<1 GV) Deep River MT (1.02 GV) Moscow MT (2.46 GV) Mt Norikura MT (11.39 GV) Nagoya MT (12.1 GV) GLE 42 on 29 September 1989 Muon telescopes 10 11:00 13:00 15:00 17:00 19:00 21:00 23:00 Time (hr:min) :00 12:00 13:00 14:00 Time (hr:min) 60 Latitude ( o ) Mex (P c = 8.15 GV) Pot (P c = 7.35 GV) Longitude ( o )

19 Solar Cosmic-Ray Spectrum from GLE Analysis The anisotropy can mask the spectral shape of the SCR intensity. Then it must first be subtracted before spectral information can be inferred. This can be done by: Fitting technique, in which the axis of symmetry of the event is determined from a network of neutron monitors (Smart et al., 1971; Cramp et al., 1997; Ruffolo et al., 2006; Vashenyuk et al., 2009) Data analysis from two very nearby stations at different altitudes (different spectral sensitivity), but asymptotic cones are so near to one another that the anisotropy effect will be small (De Koning, 1994) Ratio of increase of two cosmic-ray detectors with different rigidity response functions, but in the same location (Stoker, 1981; Bieber and Evenson, 1991; Bieber et al., 2013; Moraal and Caballero-Lopez, 2014; Caballero-Lopez and Moraal, 2015)

20 Solar Cosmic-Ray Spectrum from GLE Analysis At South Pole and Sanae Stations, two NMs with different yield functions are located one next to the another: a standard NM64 and a lead free NM (LFNM) 10-3 Yield Function (S) Diff. Counting Rate ( dn/dp) NM64: Caballero-Lopez and Moraal, 2012 LFNM: Aleksanyan et al., 1979 Proton Yield Function NM Differential Counting Rate 10 0 for Solar Spectrum: P NM64, Caballero-Lopez and Moraal, 2012 LFNM, Aleksanyan et al., Rigidity (GV) Rigidity (GV) 10/23/15 11:08 dn/dp = S x J

21 Solar Cosmic-Ray Spectrum from GLE Analysis LFNM and NM GLE 42, 29 September 1989 GLE 42, 29 September Increase (%) 10 2 South Pole LFNM South Pole NM64 Sanae LFNM Sanae NM Time (Hours) 12:00-13:00 13:00-14:00 14:00-15:00 16:00-17: Ratio LFNM / NM South Pole Sanae South Pole moving averages Sanae moving averages Time (Hours) Latitude ( o ) Latitude ( o ) Sa Longitude ( o ) Data from: Miroshnichenko et al., SP Sa SP Longitude ( o )

22 Solar Cosmic-Ray Spectrum from GLE Analysis The fractional increase at any given instant is: δn/n = Ns/Ng = P c S(P, x)a(α(p ))js(p )dp N ISO g Assuming a power-law spectrum and for a narrow asymptotic cone, the ratio of the fractional increases can be written as (Caballero-Lopez and Moraal, 2015): (δn/n) LF NM (δn/n) NM64 = NG NM64 N G LF NM P c S LF NM (P, x)p γ dp P c S NM64 (P, x)p γ dp = f(γ)

23 Power-law spectral index GLE 42, 29 September Power Law Spectral Index South Pole LFNM/NM64 Sanae LFNM/NM Baisultanova et al., 91 Kolomeets et al., 91 De Koning, Aushev et al., 93 Bieber and Evenson, 91 Oh et al., Time (Hours) Latitude ( o ) Sa SP Sa SP Longitude ( o )

24 Summary NM worldwide network: useful observational tool for SCR analysis Anisotropy masks the spectral features of the SCR Analysis of the LFNM/NM64 ratio allows to precisely determinate the SCR spectrum. This method is successful because: (a) The environmental and or other systematic uncertainties are much smaller than for the standard multi-neutron monitor method, (b) Even if the anisotropy is very large, the method is still reliable because the two instruments view in the same cone of asymptotic directions, and (c) The anisotropy effects are therefore much easier to interpret and correct for. Determination of the spectral index from a pair of narrow-cone monitors like South Pole is the most valid one. On the other hand, a pair of wide-cone monitors like Sanae is a sensitive indicator of shifts in beam direction.

25 Thank you very much!