Remote global-scale observations of intense low-altitude ENA emissions during the Halloween geomagnetic storm of 2003

Abstract

[1] Remote observations of energetic neutral atoms (ENAs) emitted from low altitude at a few keV in Earth's northern and southern hemispheres during the main phase of the 29 October 2003 geomagnetic storm are presented and compared with near simultaneous in situ measurements of precipitating ions with similar energies. A simple analysis of the ENA images yields estimates of the invariant latitudes and local pitch angles of the ENAs at their emission points. The invariant latitude distribution of the ENA emission points is similar to that of the precipitating ions and peaks near 60°. The pitch-angle distributions of the ENAs at their emission points are peaked near 90° but favor the upward (escaping) direction. We interpret the ENAs as re-emissions of the precipitating ions observed in situ, after interaction with Earth's upper atmosphere.