Characteristics of Low-Altitude Energetic Neutral Atoms: Multiple Charge Changing Interactions and Energy Loss
Tuesday, September 29, 2015
Kristie LLera1, Jerry Goldstein2, David J McComas2 and Philip W Valek2, (1)University of Texas at San Antonio, Department of Physics & Astronomy, San Antonio, TX, United States, (2)Southwest Research Institute San Antonio, San Antonio, TX, United States
Abstract:
Low Altitude Emissions (LAEs) are the energetic neutral atom (ENA) signature of ring current ions at 200-800 km. The LAE signature is produced in the so-called thick target region, i.e., by multiple charge exchange and stripping interactions in the oxygen exosphere, where each interaction results in a small net energy loss of about 36 eV. While we have an estimate of how much energy is lost per interaction, no prior study has determined how much accumulated energy is lost by 1-100 keV hydrogen ions emerging as LAEs. Our model propagates the newly created ENA with the pitch angle acquired by local magnetic field. Our model shows the energy loss is significant and comparable for parent hydrogen ions with energies below 10 keV. Each ENA cycle shifts the pitch angle to a larger v-parallel component. Ring current ions interacting with the Earth’s “optically thick” atmosphere, whether lost to the atmosphere or escaping back into space, will undergo several charge changing interactions. As such, all precipitation is a joint ion-neutral process and translational widening through ENA segments should be accounted for in determining scale structures and resolutions.
