flux and its relationship to the H
/O
transition height
not only impact the topside profile and the electron content at high latitudes
but can also affect abilities of first-principle models to differentiate
between the cause-effect terms that control the height and density of the
F
peak at midlatitudes. This was demonstrated in the work of Sica
et al. [1990] who found that the Utah TDIM could not quantitatively
differentiate between the influences of meridional winds and plasmaspheric
fluxes in the specification of F-layer heights and densities at mid-latitude
stations. The H
/O
problem was also addressed using DMSP satellite
data [ Greenspan et al, 1994] in a study of ion composition during summer
and winter solstices and the autumnal equinox under quiet,
moderately active, and disturbed geomagnetic conditions. The results
showed that regions of H
dominance were generally not symmetric about
the magnetic equator regardless of season. During solstices, light
ions tended to dominate in the entire dark winter hemisphere in both
morning and evenings at all longitudes. The DMSP results tended to
agree with earlier works and were consistent with nightside
transition heights as low as 660 km.