Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsm73a..02n&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SM73A-02
Physics
2716 Energetic Particles: Precipitating, 2730 Magnetosphere: Inner, 7837 Neutral Particles (2151)
Scientific paper
The energetic neutral atom (ENA) cameras on the TWINS spacecraft have been observing low-altitude emission (LAE) from the auroral regions during recent weak geomagnetic activitiy [ Bazell et al.; McComas et al., this Special Session]. When the observing viewpoint is favorable, LAE can be the brightest ENA emission in the TWINS images, even during large geomagnetic storms. The production of LAE is a "thick- target" process involving many collisions at altitudes <500km with monatomic oxygen (O): charge exchange of H+, stripping of neutral H, as well as energy losses due to ionization and excitation of the O when the energetic hydrogen is in either its charged (H+) or neutral (H) state. The theory of LAE therefore requires two coupled transport equations for the ion and ENA intensities. These have been developed in the extreme forward-scattering approximation. Pitch-angle changes in the Earth's magnetic field are also included, because they profoundly influence the emerging intensities of both ENAs and ions. Analytic solutions for these intensities have been obtained [ Roelof, this Special Session] that are expressed in two "eigen-functions" that are linear combinations of the ENA and ion intensities. They are functions of a "helical column density" that is accumulated by a gyrating particle during its downward path to its mirror point and then upward until its emergence as either an ENA or an ion. The solution also includes the history of the particle's energy, which constantly decreases during its trajectory due to the energy loss in every kind of atomic collision. The emergent spectra are highly directional (both with respect to the zenith and the local magnetic field vector), and they depend upon the shape of the precipitating ion spectrum. Numerical examples from the analytic solutions are presented for these functions and the emergent intensities of both ENA emission and energetic ion albedo.
Nair Hrudya
Roelof Edmond C.
No associations
LandOfFree
Computation of Emergent Intensities of ENAs and Ions From Low Altitude Emission does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Computation of Emergent Intensities of ENAs and Ions From Low Altitude Emission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Computation of Emergent Intensities of ENAs and Ions From Low Altitude Emission will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1109257