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Earthquake epicentre
Positive potential
Negative potential
Magnetic longtude (deg.)
11:00 UT
H=175 km
Fig. 4.12 The numerical grid of geomagnetic coordinates used in the model calculations and its
mesh points in which the additional potentials were set noted by the circles ( dark circles correspond
to the positive potential; light circles correspond to the negative potential)
appeared when imposing (switching on) additional potentials. The appearance of
similar magneto-conjugated regions in the opposite hemisphere is visible. The
symmetry of the potential and electric field relative to the geomagnetic equator
results from the ideal electric conductivity of the plasma along the geomagnetic
field lines and, accordingly, their electric equipotentiality. The amplitudes of the
additional eastward electric fields are about 2-4 mV/m in the low-latitude source
and 4-10 mV/m the mid-latitude source. They exceed the background quiet fields
(of about 0.2 and 1 mV/m, correspondingly), but they are noticeably smaller than the
quiet high-latitude electric fields of magnetospheric origin (15-25 mV/m) obtained
in the model calculations.
The calculated ionospheric effects in TEC and foF2 (F2-layer critical frequency)
created by the additional electric field sources are shown in Figs. 4.14 and 4.15 .
The action of the near-equatorial source intensifies the equatorial anomaly of the
F2-layer in the near-epicentral area of the ionosphere by deepening the minimum
of foF2 over the magnetic equator and displacing the anomaly crests from the
equator to the middle latitudes. This behavior agrees very well with the Alouette-1
and -2 observations (Depueva and Ruzhin 1995 ; Depueva et al. 2007 ; Ruzhin and
Depueva 1996 ).
The action of the mid-latitudinal source leads to an increase of foF2 and TEC in
the near-epicentral and in the magnetically conjugated areas. The amplitude of the
enhancements and its spatial sizes are in good agreement with the corresponding
characteristics of precursors in the TEC observations. Although the electric field
magnitudes in case of the mid-latitudinal source in our calculations are two to five
times larger than in the low-latitudinal case, the evoked effects are weaker than in
the near-equatorial regions.
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