Geoscience Reference
In-Depth Information
protons by the Explorer-10 satellite [10]. Analysis of the data established that
supersonic flow around the geomagnetic region by the solar wind must result
in the formation of a departed shock wave in front of the region. Plasma mea-
surements from the same satellite provided data on the connection between
the field and the plasma in the transition region. The movement of the mag-
netosphere boundary was repeatedly observed for 48 h. Field intensity within
the magnetosphere was larger than that of a dipole field at the same distances.
Multiple subsequent experimental and theoretical investigations not only con-
firmed the reality of the magnetosphere's existence, but also revealed in it new
important structural peculiarities - its tail, neutral layer, plasmapause, cleft,
etc.
The magnetosphere is filled with a mixture of hot and cold plasmas. Hot
protons form the so-called inner and outer Van Allen radiation belts [31]. The
inner belt is filled with high-energy protons with energy of 1
100 MeV and
it extends from 1
.
1to3
.
3 Earth's radii. The spatial distribution of protons
with energy higher than 50 MeV has two peaks: one at the geocentric distance
of 1
.
5
R
E
and with 4
−
10
3
cm
−
2
s
−
1
flux, the other at
R
=2
.
2
R
E
and with
10
3
cm
−
2
s
−
1
flux. The distribution of protons with 4 MeV energy has one
maximum at the distance of 1
.
8
R
E
and 10 cm
−
2
s
−
1
flux. Protons in the energy
range between 200 eV and 1 MeV fill the outer radiation belt. The proton flux
with peak energy of 10 keV is about 10
4
cm
−
2
s
−
1
.
The inner electron belt consists of both a natural belt and an artificial belt.
The electrons in this region are largely the result of high-altitude nuclear ex-
plosions carried out in the late fifties and early sixties. An outer electron belt
is located at 4
×
5
R
E
with a clear maximum in the distribution at 200 keV. At
distances less than 9
R
E
there is an increase in the flux of 100 keV electrons
([1], [24]).
The MHD-wave propagation in the magnetosphere is primarily determined
by the cold 0
.
1
−
−
1 eV dense background plasma. The ratio of magnetic pressure
B
2
/
8
π
to gas pressure (
nkT
) is significantly greater than one. Therefore the
Earth's magnetic field fully determines both the dynamics of the cold plasma
and its basic electromagnetic properties. The collision frequencies of charged
particles with one another and with neutral particles are considerably lower
than electron and ion cyclotron frequencies.
Within the magnetosphere, there is a special region of cold plasma, the
plasmasphere, bounded by the plasmapause. Concentration of cold plasma
inside the plasmasphere decreases monotonically with radial distance in the
equatorial plane from 10
4
cm
−
3
10
3
cm
−
3
at the inner
boundary of the plasmapause. The characteristic half-width of the plasma-
pause is in a few hundred of kilometers. On the plasmapause, the concentra-
tion drops abruptly by 1
at
R
=1
.
2
R
E
to 10
2
−
10
2
cm
−
3
. The geocentric
distance of the plasmapause is controlled by magnetic and solar activity and
fluctuates between about 6
R
E
for a quiet magnetosphere and 3
R
E
for dis-
turbed conditions ([12], [13]).
2 orders, to
N
e
=10
1
−
−
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