Relativistic Solar Cosmic Ray Dynamics in Large Ground Level Events

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Title
21-st ECRS Košice, Slovakia, 9-12 September,
2008
Relativistic Solar Cosmic Ray Dynamics in Large
Ground Level Events
E.V. Vashenuyk, Yu.V. Balabin, B.B. Gvozdevsky
Polar Geophysical Institute Apatity, Russia
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INTRODUCTION The neutron monitors (NMs) long
since and down to the present time remain the
basic means of relativistic solar cosmic rays
study. These particles are observed in rather
rare Ground Level Enhancement (GLE) events. The
rate of GLEs occurrence is 1 per year. For 66
years from the first GLE registered on 28
February, 1942, only 70 events occurred up to
now. The worldwide network of neutron monitors
can be considered as a multidirectional cosmic
ray spectrometer. The authors GLE modeling
technique employing the optimization methods and
modern magnetosphere models allows obtaining
characteristics of relativistic solar protons
(RSP) rigidity (energy) spectrum, anisotropy
axis and pitch angle distribution in the primary
solar proton flux. Two distinct populations of
RSP the prompt and delayed ones probably having
different origins on the Sun have been revealed.
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OUTLINE

• History of the GLE study with neutron monitors
• Neutron monitor network as instrument for
  relativistic solar cosmic ray studies and GLE
  modeling technique
• Results of relativistic solar cosmic ray events
  study with the GLE modeling

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Variations of cosmic ray intensity as recorded by
the neutron monitors with solar activity. By
black triangles are shown GLE occurrences.
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PGI NMs

• Two
  neutron monitor stations of the Polar
  Geophysical Institute

Apatity (67.55N 33.34E)
Barentsburg (78.08N 14.12E)
Neutron monitors computer and electronics racks
SERVER
http//pgia.ru/cosmicray
INTERNET
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Asymptotic Cone of Acceptance is formed by
trajectories of particles contributing into
response of NM
Effect of magnetosphere on cosmic rays
Barentsburg is a high-latitude station and
accepts radiation from high latitudes of the
selestial sphere and a subpolar station Apatity
from equatorial latitudes
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Anisotropy
Solar cosmic rays anisotropy effect during the
GLE on December 13, 2006
Apatity (10 s data)
Barentsburg (1 min)
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Set of NMs
The worldwide network of neutron monitors as a
multidirectional cosmic ray spectrometer
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Method 8 direct.
Scheme of asymptotic cones calculations
To account the contribution of oblique incident
particles we calculate 8 trajectories of
particles launched at zenith angle 20o and 8
azimuths
Asymptotic directions at magnetopause
SCR GCR

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Starting directions at a launching point
Calculated asymptotic directions are then used
inthe following modeling of a NM response
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GLE modeling technique of deriving the
characteristics of relativistic solar protons
(RSP) from the neutron monitor network data
consists of a few steps
1. Definition of asymptotic viewing cones (taking
into account not only vertical but also oblique
incident on a detector particles) by the particle
trajectory computations in a model magnetosphere
(Tsyganenko 2002) 2. Calculation of the NM
responses at variable primary solar proton flux
parameters. 3. Application of a least square
procedure for determining primary solar proton
parameters (namely, energy spectrum, anisotropy
axis direction, pitch-angle distribution) outside
the magnetosphere by comparison of computed
ground based detector responses with observations
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Formula

• The response function of a i-th neutron monitor
  to anisotropic flux of solar protons.
• (dN/N)i is percentage increase effect at a given
  neutron monitor i
• J(R) JoR-? is rigidity spectrum of RSP flux
  with changing slope
• ? ? ?? (R-1) where ?? is increase per 1
  GV (Cramp et al., 1997)
• S(R) is specific yield function (Debrunner et
  al., 1984),
• ?(R) is pitch angle (angle between the
  anisotropy axis given
• by ? ? parameters)
• F(?(R )) exp(-?2/C) is pitch-angle distribution
  in a form of Gaussian (SheaSmart, 1982)

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GLE 70
Increase profiles at some NM stations Oulu,
Apatity, Moscow, Barentsburg, Fort Smith
GLE 70 13.12.2006
The asymptotic cones (1-20 GV), for the above NM
stations and Th-Thule, McM-McMurdo, SA-SANAE,
Ma-Mawson, No-Norilsk, Ti-Tixie, CS-Cape Shmidt,
In-Inuvik, Pe-Pewanuk. The derived anisotropy
axis and pitch angle grid lines for solar proton
flux at 03.00 UT are shown. The cross is the IMF
direction (ACE data).
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Fitting
Observed and modeled responses at a number
neutron monitor stations --- increase profiles at
neutron monitors ??? modeling responses
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Dynamics of pitch angle distributions (PAD)
derived from neutron monitors data
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to Sun
1
3
3
1 2
Numbers mark the moments of time
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PAD demonstrates an initial highly collimated
beam of particles (prompt component) followed by
a delayed quasi-isotropic population (delayed
component)
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Dynamics of energetic spectra of relativistic
solar protons
Direct solar proton data GOES-11 TOM
intensities ? balloons, 10 UT
Spectra derived from NM data 0305
0330 0400
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GLE 20.01.2005
Increase profiles as registered by a number of NM
stations and EAS array Carpet(Baksan, North
Caucasus) The spectrum derived in moment (1 )
when the prompt component was dominated is
exponential in energy J 1.5?105exp(-E/0.92),
and spectrum of delayed component (2) has a
power-law form J 7.5?104 E-4.9. (Vashenyuk
et al.2006, 2007, Perez-Peraza et al., 2007)
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Exponential spectrum of the prompt component was
a cause of a giant increase effect at McMurdo
neutron monitor and power law spectrum of
delayed component produced rather moderate
effect at this and other NM stations during the
GLE 20.01.2005
SYF- specific yield function Debrunner et al.,
1984
a
c
b
d
Increase profiles at the McMurdo and Mawson
neutron monitors (a), rigidity spectra derived at
the moments 0700 (1) and 0800 (2) UT (b), SYF
and spectra 1 and 2 (c) differential responses
(d) of the McMurdo neutron monitor to the
exponential spectrum at the moment 1 (blue
shading) and to the power-law spectrum at the
moment 2 (red shading).
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Two relativistic solar proton components in the
GLE 23 February, 1956
(a) Increase profiles at the Leeds and Ottawa
neutron monitors (b) energy spectra derived at
the moments 0400 (1) and 0600 UT (2), (c) SYF
and spectra (1 and 2) and differential responses
of the Leeds neutron monitor to the exponential
spectrum (1,blue) and to the power-law spectrum
(2,red).
By numbers are marked, respectively, the moments
when the prompt component (1) or delayed one (2)
were dominating. One can see comparable responses
of both neutron monitors to the power-law
spectrum at moment (2).
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Results of modeling analysis of 20 major GLEs
showing existence of two RSP components
Spectrum of prompt component
JJ0exp(E/E0), E (GeV) J0, J1 (m2 s st GeV)
-1 Spectrum of delayed component JJ1E- ?
E.V. Vashenyuk, Yu.V. Balabin, L.I.
Miroshnichenko J. Perez-Peraza , A.
Gallegos-Cruz3, 30 icrc, Merida, Mx, paper 0588
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Spectra of prompt and delayed solar proton
components derived from neutron monitor data
for a number of GLEs
Delayed component
Prompt component
GLE No
GLE No
Points are direct solar proton data
from spacecrafts and balloons
Spectra of the prompt component as a rule have
exponential dependence upon energy
Spectra of the delayed component have close to
the power law dependence upon energy
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Spectra of prompt and delayed solar proton
components derived from neutron monitor data
for a number of GLEs
Delayed component
Prompt component
GLE No
GLE No
Points are direct solar proton data
from spacecrafts and balloons
Spectra of the prompt component as a rule have
exponential dependence upon energy
Spectra of the delayed component have close to
the power law dependence upon energy
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Prompt and delayed components of relativistic
solar protons (RSP)

• The modeling analysis of 20 large GLEs
  occurred in the period 1956-2006 on the data of
  the worldwide neutron monitors carried out by us
  revealed two distinct RSP populations
  (components)
• Prompt Component (PC) the early collimated
  impulse-like intensity increase with exponential
  energy spectrum,
• Delayed component (DC) the late quasi-isotropic
  gradual increase with a softer energy spectrum of
  the power law form.
• The exponential spectrum may be an evidence of
  the acceleration by electric fields arising in
  the reconnecting current sheets in the corona.
  The possible source of delayed component
  particles can be stochastic acceleration at the
  MHD turbulence in expanding flare plasma.
• E.V. Vashenyuk, Yu.V. Balabin, L.I.
  Miroshnichenko J. Perez-Peraza , A.
  Gallegos-Cruz,J ASR, V.38 (3), 411 (2006) 30
  icrc, Merida, Mexico, paper 0658 (2007)

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Results World wide neutron monitor network is an
effective tool for the relativistic solar cosmic
ray study. The modeling technique employing the
optimization methods and modern magnetosphere
models allows obtaining characteristics of high
energy solar cosmic rays rigidity (energy)
spectrum, anisotropy axis and pitch angle
distribution of the primary solar proton flux.
There is a good agreement of these
characteristics with direct measurements in
adjacent energy intervals on balloons and
spacecrafts. The presence of the prompt and
delayed components (PC and DC) of relativistic
solar protons almost in all studied GLEs (20) as
well as in superevents 23.02.1956 and 20.01.2005
has been shown. Moreover, the huge increases in
both superevents on a limited number NM stations
were caused by the prompt component having an
exponential energetic spectrum.
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