Belov A.,

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19th European Cosmic Ray Symposium
Magnetospheric effects in cosmic rays during the
unique magnetic storm in November 2003

• Belov A.,
• Baisultanova L.,
• Eroshenko E.,
• Yanke V. (IZMIRAN, Russia),
  
• Mavromichalaki H. (Athens University,
  Greece),
• Pchelkin V. (PGI, Russia)

e-mail yanke_at_izmiran.rssi.ru http//cr0.izmiran.r
ssi.ru/mosc/main.htm
2004, Florence, Italy
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Abstract

• Cosmic ray variations of magnetospheric origin
  during the severe magnetic storm on 20 November
  2003 are selected from ground level observation
  data by means of the global survey method.
  Planetary distribution of the cut off rigidity
  variations during this disturbed period was
  obtained on this basis. For this event a
  correlation between Dst index and cut off
  rigidity variation was defined for each cosmic
  ray station. The most essential shift in cutoff
  rigidities occurred while Dst index was around
  -465 nT. Geomagnetic effect in cosmic ray
  intensity at some stations reached 6-8. Cutoff
  rigidity variations were also calculated using
  the last model of magnetosphere from Tsyganenko
  2003. This magnetospheric effect seems to be the
  greatest one over the history of neutron monitor
  observations. Maximum changes of geomagnetic
  cutoff rigidities were recorded this time at
  unusual low latitudes corresponded to about 7-8
  GV cutoff rigidity. The results can be used in
  the neutron monitor data correction for
  magnetospheric effects and for the more accurate
  modeling as well of the magnetospheric current
  system during strong geomagnetic storms.

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Magnetospheric effect in CR on 20.11.03
Aurora in Athens. Foto A. Ayiomamitis.
http//www.perseus.gr/Astro-Aurorae-20031120-001.h
tm
Counting rate at different NMs uncorrected for
magnetospheric effect. FD is moderate despite of
severe magnetic storm
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DATA and METHOD Neutron
Monitors Stations used in this analysis
Global Survey Method (GSM) 1. Coupling
coefficients- beyond the atmosphere 2.
Trajectory calculations-beyond magnetosphere 3.
Spherical analysis-to select different
harmonics Counting rate -gt isotropic part3D
anisotropy magnerr
Data from 39 NMs 15 high latitudinal (lt1.2 GV),
22 mid latitude and 2 NM with Rcgt10GV
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Comparison of obtained dRc with Dst-index
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Correlation between cut off rigidity variations
dRc and Dst-index
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Latitudinal dependences of dRc for each hour
during event.

• Maximum in latitudinal distribution of dRc is
  found around 7-8 GV (usually 3-4 GV) that means
  ring current to be located at 3R.

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Comparison experimental results with calculations
by the last Tsyganenko model
1. Good agreement under Rcgt6 GV 2. Disagreement
at Rclt6GV may be caused by inadequacy of model
under great magnetospheric disturbances 3.
Experimental methods applied to other magnetic
storms gives the classical latitudinal dRc
variations with the maximum around 3-4GV

• dRc variations in dependence on cut-off rigidity
  in the maximum of geomagnetic storm 20.11.03,
  derived from experimental CR data (circles) and
  calculated by the Tsyganenko (T01storm) model
  (red).

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Compare current systems obtained directly from
experimental data and current systems obtained
from models T01s, M01, A03 for tow values of Dst
-70 and -140 nT.
Currents from the model of Tsyganenko etal. 2003 T01s
Currents from the model of Maltsev and Ostapenko2001 M01
Currents from the model of Alexeev et al. 2001,
2003 A03
Currents obtained from the database by Fairfield
et al. 1994.
Currents obtained from the database Tsyganenko et
al. 2003.
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Main conclusions.

• 1) At the beginning of extreme magnetic storm on
  20 November 2003 a small magnetosphere effect in
  cosmic rays was recorded, whereas an exclusively
  large effect was derived during the main phase of
  this storm. This allowed the latitudinal
  distribution of the cut off rigidity variations
  to be obtained for each hour during the main and
  recovery phases of this magnetosphere storm very
  useful for analysis a dynamic of evolving and
  damping out of the ring current systems.
• 2) The ring current system during magnetic storm
  on 20 November 2003 was at more close distance
  from Earth (apparently about 3 Earths radii)
  than it usually observed. As a consequence,
  maximal magnetosphere effect in CR was recorded
  at lower latitudes, but not at the mid latitude
  stations as usual. Maximum changes of the
  geomagnetic cut off rigidity were shifted due to
  this anomalous from 3-4 GV (usually) to 7-8 GV.
• 3) The calculations of Rc changes performed for
  the last "storm" model T01s of the magnetospheric
  magnetic field 12 shows a good agreement
  between experimental and theoretical values for
  rigidities gt 6 GV. Possibly, the model is not
  adequate for the greatest magnetospheric
  disturbances, this causes a discrepancy for lower
  rigidities.
• 4) Further developing and extended variant of
  this work, whether another events are analyzed,
  can be found on http//cr0.izmiran.rssi.ru/GeoMa
  gCR/main.htm .

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