Geoscience Reference
In-Depth Information
Fig. 4.11
UAM model results of two further time moments, 02:30 UT (
left
) and 04:00 UT (
right
),
during CHAMP overflights over the southern polar region from afternoon hours (
14 MLT) to
midnight (24 MLT), presented in the same manner as in Fig.
4.10
. The actual solar wind and IMF
condition differ: in both cases we have predominantly negative IMF B
y
,butthe
B
y
component is
much more intense for the later moment (cf. Fig.
4.7
). Please note the different scales for the wind
vector and electric potential presentations, being considerably larger for the
right panel
The mentioned discrepancies during other example orbits were likely related
to the initial neglect of the IMF dependence of the convection electric field, in
particular on its
B
y
component. The behavior of this component during 28 October
2003 is shown in Fig.
4.7
. We performed a series of numerical experiments to
improve the model's boundary conditions of the Region-1 FACs as one of the
primary sources of energy and momentum input at high latitudes, which had to
accompany a corresponding adjustment of the high-energy precipitations at auroral
and polar latitudes.
Figure
4.11
shows the comparison of two consecutive CHAMP overflights
over the southern polar region, displaced by the orbital period of
90 min. Both
periods were characterized by near-zero IMF
B
z
and a negative IMF
B
y
component,
which carried out a jump-like intensification from
5nTto
15 nT between the
two orbits (see Fig.
4.7
). The more correct description of the IMF dependence
of the Region-1 FACs, particularly of its strong pattern-shaping by the IMF
B
y
component (larger round-shaped dusk convection cell for negative B
y
at the
Southern Hemisphere; see Fig.
4.3
), resulted in much better agreement between
model values and observations. The strong increase of the neutral wind component
velocities for the later time moment (note that the scales for electric potential and
wind amplitudes are different for the two panels of Fig.
4.11
) is obviously the result
