Geoscience Reference
In-Depth Information
Z
l
B
1
d
z
;
j
==
D e
z
Œ
r
V;
r
p
i
=B; V
D
B
(4.25)
0
where
j
//
is the field-aligned current density,
E
and
B
are the electric and geomag-
netic fields,
e
z
is the field-aligned (along
B
) unit vector,
V
is a half-volume of the
geomagnetic field tube,
z
is a distance along the geomagnetic field line,
l
is the
value of
z
at the top of the geomagnetic field line,
p
i
is the magnetospheric ion gas
pressure considered isotropic and constant along the geomagnetic field line,
n
i
is the
magnetospheric ion concentration,
V
i
is the magnetospheric ion drift velocity, and
e
is the electron charge. The magnetospheric electrons are considered to be cold, and
their pressure is neglected in comparison with that of the magnetospheric ions. The
geomagnetic field is considered as a dipole at latitudes equatorward of the polar cap
boundary (˚
D
75
ı
) and having the field lines opened inside the polar cap areas.
4.2.5
Inputs of the Model
The input parameters of the model are (1) solar UV and EUV spectra; (2)
precipitating particle fluxes; (3) field-aligned currents connecting the ionosphere
with the magnetosphere and/or the electric field potential distribution at the polar
cap boundaries; and (4) vertical currents at the lower ionospheric boundary flowing
from the lower atmosphere. For the solar UV and EUV fluxes and their dependencies
on solar activity we use the data from Ivanov-Kholodny and Nusinov (
1987
).
Intensities of night sky scattered radiation are chosen equal to 5 kR for
D
121.6 nm
and 5 R for each of the other emission lines (œœ
D
102.6 nm, 58.4 nm, and 30.4 nm).
Spatial distributions of the precipitating electron fluxes are taken at the upper
boundary of the thermosphere (
h
D
520 km) in a simple form:
I.˚;;E/
D
I
m
.E/exp
h
.˚
˚
m
.E//
2
.
.˚.E//
2
.
m
.E//
2
.
..E//
2
i
(4.26)
˚
m
D
.˚
md
C
˚
mn
/=2
C
.cos/.˚
md
˚
mn
/=2
(4.27)
where ˚, are geomagnetic latitude and longitude,
D
0 corresponds to the
midday magnetic meridian,
I
m
(
E
) is the maximum intensity of the precipitating
electron flux,
E
is the energy of the precipitating electrons, and ˚
md
, ˚
mn
are the
geomagnetic latitudes of the maximum precipitation at the midday and midnight
magnetic meridians. All precipitation parameters (
I
m
, ˚
md
, ˚
mn
, ˚,
m
, )
can vary depending on geophysical conditions.
The magnetospheric sources of the electric field are field-aligned currents in
Region-1 and -2 and in the cusp region (Iijima and Potemra
1976
). The Region-
1 field-aligned currents, flowing into the ionosphere on the dawn side and out on the
