1. Athens University – Faculty of Physics Section of Nuclear and Particle Physics Athens Neutron Monitor Station Study of the ground level enhancement of 20 January 2005 1.University of Athens, Physics Dpt., Nuclear and Particle Physics Section 2. Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN) C. Plainaki (1), A. Belov (2), E. Eroshenko (2), H. Mavromichalaki (1) V. Yanke (2) 20 th European Cosmic Ray Symposium in Lisbon, Portugal September 5th-8th 2006

2. Overview Solar activity in January 2005 – (GLE 69) A new GLE Model Application to GLE 69 Results of modeling Conclusions

3. Solar Activity related to GCR variations in January 2005

4. GLE on 20 January 2005 High latitude NM stations Mid latitude NM stations Increase of ~ 3353 % (South Pole) ~ 2093 % (Mc Murdo)

5. GLE 69 Characteristics (derived from analysis of data from 41 NM stations) GLE onset for most stations: 06:50 – 07:00 UT Different time of maximum flux among the stations. First maximum recorded at South Pole (06:50 UT). Last maximum recorded at Thule (07:30 UT) Biggest maximum was observed at South Pole. Maximum rigidity of solar particles arriving in the vicinity of Earth at least 14.1 GV !   Evidence of anisotropy : Two orders of magnitude difference in maxima between McMurdo (south hemisphere) and Thule (north hemisphere).

6. The method of coupling coefficients (Dorman, ????) Intensity of any CR component of type, observed at a cut-off rigidity, at level in the atmosphere at some moment : Possible time variation of observed CR intensity can be caused by the variation of any of the three parameters :, or Primary CR spectrumIntegral multiplicity where: is the coupling function between secondary CR of type and primary CR

7. Modeling GLEs where the coupling function is defined as: (Dorman, 2004;Clem and Dorman, 2000; Belov and Struminsky, 1997; Belov et al., 2005) where is the Dorman function Solar Cosmic Rays differential spectrum

8. Neutron Monitor Coupling Functions

9. Modeling the GLE of 20 January 2005 is a typical Forbush GCR spectrum where 2) SCR spectrum 1) Neutron monitor coupling functions: is an axis-symmetric anisotropy functionwhere rigidity dependence of the SCR differential spectrum

10. Definition of the angular parameter Ω Point of observation Location of the anisotropy source

11. GLE model Application Five minute data from 41 NM stations widely distributed around the Earth Magnetospheric field configuration according to Tsyganenko89 model Calculation of the Neutron Monitors asymptotic directions of viewing. Levenberg-Marquardt non-linear optimization algorithm

12. Results Goodness of our fit for the first time intervals of the event Goodness of our fit for the first time intervals of the event For later moments the dispersion between observed and calculated CR variations was reduced, whereas the correlation coefficient remained big enough.

13. Rigidity Spectrum   Contribution of higher energy particles in 6:45 – 6:50 UT   Initially hard spectrum- significantly softer in the second 5min-interval- hardened during the third one  quite an unexpected behavior!   Peak spectrum quite close to power law  Contrary to the 15 June 1991 event, the form of peak and emission spectra during GLE 69 cannot be supposed as coincided!   Even in case of a full scatter-free propagation the peak spectrum cannot be affirmed to be very representative of the injection spectrum shape because of the possible influence of the magnetic field  Additional study required

14. Differential proton fluxes   Peak time turned out to be the same for all higher rigidity particles (1GV, 2GV and 3GV)   The proton enhancement in the vicinity of Earth for solar particles must have been of very short duration.   A difference in the profiles for 1GV and 2GV might be an argument for two episodes of the acceleration.

15. Integral proton fluxes   Big mean integral flux during the first time intervals of the event   Good agreement of the calculated mean integral flux with the satellite observations.   According to our model, all three fluxes of lower energy particles remain at a surprisingly high level during the first hour of the event. This is also testified by the satellite observations.   The estimated flux for particles with energy >100 MeV exceeds only by a factor of ~2 the flux recorded on 29 September 1989 (~600 pfu) and on 14 July 2000. Results displayed for energies greater than 100 MeV, 200 MeV and 300 MeV are obtained by extrapolation

16. Anisotropy   Strong anisotropy during the first moments of the event. The anisotropy contribution in mean fluxes coincides with that in maximum fluxes.   The angular distribution is narrow during the time interval 6:45 UT – 7:00 UT, with an index taking values between 3 and 15.   After 7:00 UT anisotropy index becomes smaller (~1), suggesting a wider angular distribution of SCR particles   Position of the anisotropy source (VIDEO???)

17. Longitudinal distribution of the anisotropy

18. Interplanetary Magnetic Field   The IMF in the time-interval 6:00 UT-7:00 UT is placed to 135 0 west from the Sun- Earth line.   In the initial phase both directions of IMF and anisotropy are quite close.  perhaps these particles have arrived being directed almost along the IMF lines.   Later more complicated particle propagation, since the anisotropy and the IMF directions differ significantly. Angular difference between the IMF and the projections of the anisotropy on the ecliptic plane.

19. Contour areas of equal fluxes of particles with rigidity>1 GV together with NM asymptotic viewing directions

20. Conclusions   The event of 20 January 2005 is ranked among the greatest GLEs in the history of observations.   The event of 20 January 2005 has a complex structure with two maxima. The first maximum appears due to the extremely anisotropic beam of solar particles arriving during the initial phases of the event, whereas the second one is probably related to SCR density maximum.   The time evolution of the rigidity spectrum has a rather complicated behavior. In the beginning of the event it appears hard. In the second time-interval it softens abruptly and then it hardens again. During the later phases the spectral index varies between -6.6 and -7.6.   The extremely intensive narrow beams of solar relativistic particles arriving at the Earth during the time interval 6:50 UT – 6:55 UT had a width that did not exceed 10-40 degrees.   The neutron monitors whose asymptotic directions at that time viewed the anisotropy source recorded enhancements of thousand of percents (e.g. McMurdo, South Pole). These initially narrow particle beams widened with time resulting in big enhancements recorded by all other high latitude NMs.

21. Conclusions   Anisotropy remained in relatively high levels during the first hour of the event.   The source of anisotropic flux was located in southern hemisphere. The position of the anisotropy source changed with time, moving to more northern locations.   The estimation of the integral flux for particles with energy >100 MeV on the basis of our model is in good agreement with the satellite observations.   Many features of this GLE may be explained by the peculiarity of the particle interplanetary propagation.