Geoscience Reference
In-Depth Information
Fig. 11.16
Numerical
simulation of magnetic
perturbations in the polar
magnetosphere. The extrinsic
current at the lower boundary
of the ionosphere is modeled
by the delta-function of time.
The components B
z
, B
r
,and
B
'
versus
B
, nT
40
1
2
3
30
l/=V
A
are shown with lines 1, 2, and
3, respectively (Surkov
1996
)
D
t
.
z
20
10
t
, s
0
0,05
0,10
-10
-20
-30
-40
of the dayside ionospheric E-layer; that is,
P
D
0:5
H
D
2:5
10
4
S=m,
V
A
D
300 km=s as well as the following numerical values b
D
3 km, a
D
100 km,
r
D
90 km, T
D
0:1 s.
Next consider the case when the source function/extrinsic current is modeled by
a step function of time, that is J
H
.r;t/
D
H
B
0
V
r.a
r/T.t/=a.Inthis
case the integrals in Eqs. (
11.52
) and (
11.53
) are not expressed by the elementary
functions though the component B
r
can be written as
0
H
2
1=2
B
0
V
br
aV
A
B
ri
D
G
z
.l;/:
(11.62)
For this extreme case the results of numerical calculations are shown in Fig.
11.17
.
As is seen from Figs.
11.16
and
11.17
, the risetime of the signals is approximately
coincident with that of the exponential factor exp
ǚ
0
P
l
2
=.4/
. This time is of
the order of diffusion time through the conducting
E
-layer t
d
0
P
l
2
=4
0:07 s.
The oscillations with the phase
0
H
l
2
=.4/ are due to the Hall conductivity of the
ionospheric plasma. The period of oscillations increases in time until they disappear
at the moment t>t
o
D
0
H
l
2
=4
0:05 s. The substitution of the step function
Search WWH ::
Custom Search