Geoscience Reference
In-Depth Information
Fig. 1. Sketch of a reconnected field line on the dayside magnetopause, illustrating the
key parameters associated with the
de Hoffmann-Teller
(HT) reference frame:
V
A
-
SH
and
V
A
-
SP
are the Alfvenic speed (tangent to the local magnetic field) on the magnetosheath
and the magnetospheric side, respectively;
ϕ
and
θ
are the angles formed by
V
A
-
SH
and
V
A
-
SP
with the magnetopause (dashed grey line);
V
SH
is the magnetosheath flow
velocity (black arrow tangent to magnetopause); and
V
HT
is the HT reference frame
velocity (white arrow).
to determine the minimum (
V
min
), peak (
V
p
), and maximum (
V
max
)velocity
of the ions crossing the magnetopause along open field lines (please, refer
to Ref. 3 for a more detailed discussion):
V
SH
=
−
V
A
-
SH
cos
ϕ,
(1)
V
HT
=
V
SH
+
V
A
-
SH
cos
ϕ,
(2)
V
min
=
V
HT
cos
θ,
(3)
V
p
=
V
HT
cos
θ
+
V
A
-
SP
,
(4)
V
max
=
V
HT
cos
θ
+
V
A
-
SP
+
V
th
.
(5)
The acceleration of the injected plasma critically depends on the ratio
between the Alfvenic speed on the magnetospheric (
V
A
-
SP
) and magne-
tosheath (
V
A
-
SH
) sides. In this work, we assumed
V
A
-
SP
=5
V
A
-
SH
, while
the
V
A
-
SH
speed was derived from the model. As in a previous analysis,
3
the magnetosheath plasma velocity
V
SH
,density
N
SH
, and temperature
T
SH
,
close to the magnetopause, were derived from the work of Spreiter
et al.
4
At
the orbit of Mercury, the presence of a significant
B
x
component causes the
plasma to precipitate mainly in the dayside hemisphere that is directly con-
nected to the IMF. This is due to the reduced plasma penetration through
the open magnetic field lines that are draped in the antisunward direction,
forming the polar cap regions. Our results suggest that the magnetic recon-
nection geometry causes the focusing of the plasma injection within confined
