PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
and right sides of this equation, respectively. The physical sense of this expression is clear. If gas moves
toward increasing pressure, then Ej >0. We have an electric power consumer: MHD compressor. If plasma
flows toward decreasing pressure, gas kinetic forces can do the work over electric forces. Knowing plasma
pressure distribution, we can easily determine the locations of the MHD compressor and MHD generators in
the magnetosphere. MHD generators were at least three. The first generator is located at the inner boundary
of the plasma sheet. This generator operates on a radial gas pressure gradient ∇rp; two other generators
operate on longitudinal gradients ∇λp (for more detail, see [Ponomarev, 1985; Ponomarev, Sedykh, 2006]).
Generators feed the Birkeland-Bostrom (BB) current systems of the first and second types. Here we note that
actually physically substantiated sources of power for electrojets were for the first time proposed in
[Ponomarev, 1985]. The electric scheme of electroject connection was proposed in the same work (Fig. 5).
Figure 5. Schematic spatial location
of the magnetospheric-ionospheric
currents: (a) the system of feeding
the meridional currents, (b) the
system of feeding the latitudinal
currents, and (c) the equivalent
scheme of the magnetosphericionospheric
current circuit.
This scheme was based not only on the formula (12) but also on the expression for the field-aligned currents
[Ponomarev, 1985] (see fig. 6):
jll = cB I {[∇pg×∇pB]⋅B/pB B 3 l
∫
}dl (13)
0
where В I is the magnetic field strength in the ionosphere, the integral is taken over the entire flux tube from
the equator to the ionosphere, and рВ is the magnetic pressure. The expression for jll is well-known
Vasyliunas-Tverskoy’s expression for FAC. It is clear that the integrand in (13) is proportional to the sine of
the angle between the contour lines pg=const and pB= const. In a dipole approximation, lines of equal
magnetic pressure are concentric circles, and isobars follow plasma pressure relief contour lines. It is clear
that in this case the field-aligned currents are concentrated on an amphitheatre crest and vanish and change
the sign at the crest top point. In the case shown in fig. 5, we have only the current corresponding to the BB
loop of the first type. In this case only westward current is observed in the ionosphere. The BB loop of the
second type with short sections of meridional currents in the ionosphere originates at a more complicated
pressure configuration.
a) b) c)
60 60
70
80
1 2
70
80
60
70
80
Figure 6. Results of calculations of the
field-aligned currents as divergence of
the magnetospheric bulk currents;
(resulted from the convergence of the
contour lines of the gas and magnetic
pressures): (a) t = 0 s, (b) t = 1000 s, and
(c) t = 2800 s. (1) and (2) the zones of
inflowing and outflowing currents.
The second amphitheatre and a specific corridor between the amphitheatre and the main crest appear in Fig.
3b. The cross section of this spatial pattern along any intermediate contour line is represented by plasma
corridors (channels of MHD-generators). The field-aligned currents are directed oppositely on both sides of
the corridor. Since the sign of the pg gradient changed and that of the pB gradient remained unchanged, the
double "curtain" of field-aligned currents is formed, which is a characteristic feature of auroral electrojet
feeding. The geometry of these electrojets corresponds to that of the BB current loop of the second type. We
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