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Shepherd et al., [2002]
identified quasistable periods of , the KanLee
electric field
[Kan and Lee, 1979],
as measured by the Advanced Composition
Explorer (ACE) between February 1998 and December 2000. These periods also
satisfy the criteria that
, determined using the Johns Hopkins
University Applied Physics Laboratory Fitting technique or APL Fit
[Ruohoniemi and Baker, 1998;
Shepherd and Ruohoniemi, 2000],
were suitably welldefined by the SuperDARN LOS Doppler velocity data.
Figure 1.
Global convection map and
derived from SuperDARN velocity
data for an example 10min period during this study. The dots indicate anchor
points of the velocity data and contours represent constant potential
curves.

Figure 1 shows an example of a global convection map for a 10min
period from the
Shepherd et al., [2002] study.
For this period SuperDARN LOS velocity data were obtained over large portions
of the dawn and dayside sectors. The coveraged was sufficient to fix the values
of the potential extrema and hence to determine
.
We use a subset of 1317 10min periods from the
Shepherd et al., [2002]Shepherd:00 dataset
for this study. Because the statistics are greatest in the range
30 kV/R, we use only the periods which fall in this range.
Appropriately timelagged 10min averages of the ACE/SWEPAM solar wind speed
() and mass density (), and the ACE/MAG IMF () are used to
derive
.
is also computed for the Boyle model
[Boyle et al., 1997] for comparison.
for these models are then directly compared to the SuperDARNderived
transpolar potential (
).
The formulation of the Hill model we use in this study is given by
[Siscoe et al., 2002]

(1) 
where
is the solar wind electric field with
being the solar wind speed and
. is the solar wind ram pressure.
is the IMF clock angle dependence of reconnection at the magnetopause, taken
to be
. A relation for , a factor that depends on the
geometry of the currents flowing into the ionosphere, is given as
, where is the ionospheric conductance and is assumed to
be uniform. We note that the choice of allows us to rewrite
(1) as

(2) 
where is identified as the KanLee reconnection electric
field
[Kan and Lee, 1979]
corresponding to the fastest merging rate at the subsolar magnetopause
[Sonnerup, 1974].
Next: Data and Discussion
Up: Testing the Hill model
Previous: Introduction
Simon Shepherd 20020604