Geoscience Reference
In-Depth Information
a
b
M
Fig. 11.5
Distortion of the geomagnetic field lines caused by the expansion of a highly heated
plasma ball. (
a
) Equidistant field lines of undisturbed magnetic field
B
0
;(
b
) Field line pattern
resulted from the conducting plasma motion. The
closed “circular” lines
indicate the currents
induced in the plasma ball. The effective magnetic moment is shown with vector
M
depends on the current system in the plasma. In order to find the value of this
moment we use the boundary condition which requires the continuity of the normal
component of ı
B
at the plasma ball surface. Equating the normal component of
magnetic perturbations in Eq. (
11.7
) with that given by Eq. (
7.5
)atr
D
R,we
obtain
0
M=
2R
3
D
1
R
0
=R
2
B;
(11.8)
hence it follows that the effective magnetic moment of the plasma ball is
1
:
2
B
0
R
3
0
R
0
R
2
M
D
(11.9)
Substituting Eq. (
11.9
)for
M
into Eq. (
7.7
) one can find the radial ıB
r
and tangential
ıB
components of the GMPs
r
3
1
R
2
cos ;
R
3
R
0
ıB
r
D
B
0
(11.10)
2r
3
1
R
2
sin :
R
0
ıB
D
B
0
R
3
(11.11)
Here is the polar angle measured from the direction of
B
0
.
As is seen from Eqs. (
11.10
) and (
11.11
) the magnitude of EMP decreases with
distance inversely proportional to the distance cubed. Substituting the following
numerical parameters B
0
D
5
10
5
T, R
D
30 m, R
0
D
1 m, and r
D
7 km
Search WWH ::
Custom Search