1. Introduction
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Figure 1
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[2] Extreme development of solar processes at the end of October 2003
led to prominent magnetic storms on 29 and 30 October. Anomalous
speeds of the solar wind reaching 2000 km s
-1 were registered in this
period. The value of the
Bz component in some
moments was
-(40-50) nT. The estimates of the electric field of the solar wind showed
that its magnitude also reached extreme values up to 40-50 mV m
-1 [see, e.g.,
Panasyuk et al., 2004].
The extreme development of the
processes on the Sun at the end of October 2003 and the further
extreme development of auroral and geomagnetic disturbances led to a
principal changes in the structure and dynamics of the magnetosphere
and ionosphere in this period
[Ivanov et al., 2005;
Lopez et al., 2004;
Panasyuk et al., 2004;
Veselovsky et al., 2004;
Webb and Allen, 2004;
Woods et al., 2004;
Zherebtsov et al., 2005].
The disturbances were
covering the entire thickness of the ionosphere. The auroral processes
typical for high latitudes shifted to middle latitudes where only limited
experimental means for observation of auroral processes are available.
Analysis of VLF signals is one of the methods of observations of
disturbances at middle latitudes in the considered period of time. The
VLF signal characteristics are very sensitive to variations in the
ionospheric
D region
[see, e.g.,
Rishbeth and Garriott, 1969].
Therefore studies of the changes in VLF propagation conditions at
space separated midlatitude paths (see Figure 1) provide a possibility
to study the development of ionosphere-magnetosphere disturbances
including the regions of injection of charged particle fluxes into the
ionosphere in the regions where there is no means for registration of
auroral events.
[3] The goal of this paper is studying of the variability of the electron
concentration in the ionospheric
D region after the solar flares on 28
and 29 October 2003 and the following development of magnetic
storms on 29 and 30 October 2003 and also analysis of the shifts and
dynamics of the boundaries of charged particle precipitation regions.
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