Global imaging of O+ from IMAGE/HENA

Donald G. Mitchell, Pontus C:son Brandt, Edmond C. Roelof, Douglas C. Hamilton, 
Kyle C. Retterer and Steven Mende


The magnetospheric O+ population in the 52�180 keV range during storms is
investigated through the analysis of energetic neutral atom (ENA) images. The
images are obtained from the high energy neutral atom (HENA) imager onboard the
IMAGE satellite. At each substorm onset following the commencement of a
geomagnetic storm the oxygen ENA display �`30 min intense bursts. Only very weak
corresponding features in the 60�119 keV hydrogen ENA can be occasionally seen.
The dominating fraction of the oxygen ENA emissions are produced when O+ ions
mirror/precipitate at low altitudes, where the number density of the neutral
atmosphere is high. During the storm we observed several bursts of oxygen ENA,
but it is still not clear how much the O+ content of the ring current increases
during the storm main phase. Our observations suggest that the responsible
injection mechanism is mass-dependent and scatters the pitch angles. This leads
us to favor a non-adiabatic mechanism proposed by delcourt 2002.

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Space Science Reviews, 109, 1-4, p. 63-75, 2003