Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13d2102b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM13D-2102
Astronomy and Astrophysics
Astrophysics
[0328] Atmospheric Composition And Structure / Exosphere, [0394] Atmospheric Composition And Structure / Instruments And Techniques, [2794] Magnetospheric Physics / Instruments And Techniques, [7549] Solar Physics, Astrophysics, And Astronomy / Ultraviolet Emissions
Scientific paper
The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission images the magnetosphere in energetic neutral atom (ENA) fluxes, which are produced in charge exchange between magnetospheric energetic ions and background exospheric hydrogen (H) atoms. To derive ion properties from ENA measurements, knowledge of the exospheric H density distribution is necessary. Exospheric atomic hydrogen resonantly scatters solar Lyman-alpha (121.567 nm) radiation, creating a phenomenon known as the geocorona. Consequently, in addition to ENA imagers, TWINS includes Lyman-alpha Detectors (LADs) to register line-of-sight resonance scattered intensities of the geocorona. We use LAD measurements to obtain global H density distributions for geocentric distances above 3 earth radii. Observations of the geocorona reveal an exosphere that is asymmetric, with a persistent night-side extension, sometimes called the geotail. We present first sets of derived exospheric distributions at different seasonal conditions. A seasonal north-south asymmetry occurs as solar illumination differs between the summer and winter polar regions. Pole-equator and less pronounced dawn-dusk asymmetries also appear, possibly due to a coupling effect via charge exchange with the polar wind and plasmasphere, respectively. The sequence of exospheric distributions enables studying of the response of the exosphere to seasonal (solstice and equinox) variations.
Bailey Jeremy
Gruntman Mike
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