Neutral polar wind

Larry C. Gardner and Robert W. Schunk


The classical polar wind is an ambipolar outflow of ions from high latitudes
along open geomagnetic field lines. The polar wind consists of light thermal
ions (H+, He+) and energetic light and heavy ions (H+, He+, O+). The
characteristics of these ions have been studied quite extensively since the
1960s. In just the last 20 years, however, energetic neutral atoms (ENAs) that
are produced in charge exchange reactions between the singly ionized polar wind
ions and the surrounding neutral atoms have been used as a means to remotely
probe plasma populations. Recent estimates for neutral outflow integrated fluxes
from the LENA instrument on the IMAGE spacecraft have shown values of 1Ð4 X 10E9
cm-2 s-1, with a considerable diurnal variation. A theoretical model has been
used in this study that is similar to the high-latitude hydrodynamic polar wind
model developed at Utah State University, but it has been expanded to include
the effects of neutral stream particles so that the characteristics of the
neutral polar wind can be elucidated. The neutral polar wind model results show
a high neutral hydrogen outflow flux on the order of 10E9 cm-2 s-1.

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Journal of Geophysical Research, 109, A05301, doi:10.1029/2003JA010291, 2004