Global, extended energy observations of the oxygen ring current during large storms

Abstract:

During large goemagnetic storms, it is known that oxygen can be a significant fraction of the ring current. Global, composition separated observations of the inner magnetosphere have been made using Energetic Neutral Atoms (ENAs) with the IMAGE / High Energy Neutral Atom Imager (HENA) and by the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission. HENA observed the high energy O ENA population ( 50 to >180 keV), while the middle energy range (16 - 32 keV) is observed by the TWINS mission. The ENA observations from TWINS show that during storm time, the mid energy O population evolves on time scales on the order of hours. In contrast, HENA observations of high energy ENAs O showed that this population varied on a much shorter - sub-storm like - timescale. Unfortunately, the TWINS medium energy and HENA high energy observations were not performed simultaneously. In fact, the HENA (2000 to 2005) and TWINS (2008 to present) observations are not even from the same solar cycle. The TWINS ENA sensor is capable of measuring both the mid and high energy O populations, but until recently reliable mass separation was not possible at higher energies due to limitation of the calibration . The energy range where TWINS makes reliable global O ENA observations has been extended to > 150 keV thanks to recent laboratory testing with a high fidelity engineering unit. We will present the first composition separation, ENA images that span both the medium and high energy ranges. We will show simultaneous observations of the timescales for both energy populations during large geomagnetic storms.