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Since the
high-latitude ionosphere is very irregular as a result of
time-dependent particle precipitation patterns and convection
electric fields, there have been attempts to capture some of
its climatological characteristics in terms of averaged specifications
of the auroral oval boundaries, convection electric fields, and
total electron content (TEC). Crain et al [1993] used four
northern high-latitude stations to develop monthly-averaged TEC data
for January and June during solar maximum and minimum. They included
fitted numerical model simulations (the Utah State TDIM) which
employed empirically-specified patterns for auroral precipitation
and magnetospheric/ionospheric convection electric fields to
extend predictions of high-latitude climatology to latitudes other
than those defined by the ground-based stations. Comparison of the
model results with the observations showed relatively good
qualitative agreement in the diurnal characteristics but poor agreement on
a quantitative level. In particular, the model tended to
underestimate the night-time TEC. The suggested source of error was
the plasmaspheric H
flux, which the model neglected.
U.S. National Report to IUGG, 1991-1994
Rev. Geophys. Vol. 33
Suppl., © 1995 American Geophysical Union