PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
Figure 2. SEP penetration boundary variations during geomagnetic storms in May
2005. Dst-variation is shown by solid line.
Because the proton flux on the penetration boundary does not fall down abruptly, it is possible to apply
different criteria to the analysis of the penetration boundary position. Along with (Kuznetsov et al., 2002),
we have used the traditional for Skobeltsyn Institute of Nuclear Physics Lomonosov Moscow State
University criterion - twice below the maximum of the SEP flux. The values of penetration boundary
obtained during the morning MLT are marked as open symbols, during evening MLT – as closed ones. The
time variation of the Dst index is also shown in Figure 1 for comparison. We can see that penetration
boundary variations correlate with Dst in accordance with (Panasyuk et al., 2004, Kuznetsov et al., 2005).
The dashed line on the Fig. 2 represents the distance to the inner edge of the magnetospheric tail
current – projection of the equatorward boundary of the auroral oval at midnight to the geomagnetic equator.
This distance was obtained on the base of magnetic field calculations by paraboloid model of the Earth's
magnetosphere (Alexeev et al., 2001). We can see that during storm maximum penetration boundary lies
below the auroral oval in the region of trapped particles, while during recovery phase it shifts to the higher
latitudes. Obviously, during magnetic storm main phase there exist the additional mechanisms transporting
energetic particles from solar wind to magnetosphere on the closed L-shells.
During storm maximum SEP approached latitudes corresponding L-shells about 2.5. It is accepted that
SEP fluxes are measured in the region of open field lines, but latitudes with L=2.5 can be hardly associated
with open magnetic field flux tube. It is interesting to compare the obtained results with those obtained from
the other experimental sources or model calculations. Figure 3 represents auroral oval observed by IMAGE
WIC instrument at 06:25:31 15 May 2005 (data from http://workshops.jhuapl.edu/s1/science.html), and SEP
penetration boundary cross-sections by CORONAS-F satellite pass through the polar cap measured at 6.42
UT and 6.72 UT. These time moments correspond to the storm main phase. Electric field equipotentials in
the polar cap calculated by mapping of electric potential from the magnetopause along the open field lines
are shown by pink lines. They fill the area that can be associated with polar cap. We can see that SEP
penetration boundary lies on the latitudes lower than not only the polar cap but also than whole auroral oval.
The experimental data and the results of calculations in four time moments before the storm, during
storm maximum and during recovery phase are presented in the Table 1. The values of the proton flux with
the energy 1-5 MeV, magnetic local time (MLT), geographic latitude and longitude (LAT) (LON), magnetic
latitude and longitude (MLAT), (MLON), experimental and calculated L-shell values are shown. The Lcoordinate
of the ionospheric point is often considered as the distance to its projection to geomagnetic
equator along the magnetic field line.
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