The more global-scale magnetospheric issues concerning ionospheric plasma
flow to major magnetospheric regions were examined during this quadrenial
period with single-particle trajectory tracing and energetic ion composition
measurements. In the former category, Delcourt and colleagues
considered several aspects
in the ion trajectory tracing of large-scale transport of ionospheric ions.
For example, Delcourt et al. [[1990]]
have modeled the storm-time transport
of ionospheric plasma from the dayside polar cleft ion fountain
into the ring current.
Modeling
the transition in middle magnetosphere magnetic field configuration from
taillike to dipolelike, they show that such transport may energize O
into the range several keV to several hundred keV, with accompanying pitch
angle trapping. Hence, the cleft ion fountain may make a substantial
contribution to the ring current formation during dipolarization events.
Delcourt et al. [[1993]; [1994]] also
used particle trajectory modeling
to analyze the large-scale transport of the polar wind and cleft-originating
ions into the plasma sheet and magnetotail.
They find that during quiet times
the polar wind may access the distant magnetotail and may be trapped
by non-adiabatic scattering processes, and hence should
be an important source for the nightside central plasma sheet population.
Cladis and Francis [[1992]] used ion trajectory modeling
to calculate the effects of cleft-origin O
on the plasma sheet pressure
distribution and suggested that these effects might alter the magnetic
and electric field distributions sufficiently to trigger substorms.
Observational U. S. contributions to our understanding of ionospheric
plasma in the outer magnetosphere were made chiefly by the Lockheed
group.
Lennartsson [{[1994]] analyzed a large set of International
Sun-Earth Explorer-1(ISEE-1)
energetic (0.1-16 keV/e)
ion composition data from the central magnetotail between 10 and
23 R
geocentric distance, and showed that H
exhibits a steeper
density gradient than O
. The data of
Lennartsson [{[1994]] further supported the
idea that tail lobe convection is directed inward from the dawn
and dusk flanks. Lennartson et al. [[1993]] also
examined the
concept(noted earlier)
that significant populations of energized O
may
serve as a trigger or amplifier for substorms/geomagnetic activity.
However, their correlation studies do not support this concept,
although O
is found to
constitute the bulk of the mass density in the tail current sheet.
Ionospheric composition(and other aspects) of
regions near the magnetopause were
studied by Fuselier and co-workers.
Fuselier et al. [[1991]] examined Active Magnetospheric
Particle Tracer Explorer(AMPTE) ion composition
data from the dayside magnetosheath region to investigate the origin of
energetic ion events there. Although most of the observed energetic ions
appear to be of solar wind origin, the occasional presence of magnetospheric
O
suggests occasional leakage from the dayside magnetosheath.
Fuselier et al. [[1993]] also examined the
general mass density and
pressure changes across the dayside magnetopause using measurements from
AMPTE. On most occasions, H
was the dominant mass
and pressure contributor in the magnetosheath and low-latitude boundary
layer(LLBL), but in one of their observations O
was the dominant contributor
to the LLBL.