Experimental Study of Exospheric Hydrogen Atom Distributions by Lyman-alpha Detectors on the TWINS Mission

Details Experimental Study of Exospheric Hydrogen Atom Distributions by Lyman-alpha Detectors on the TWINS Mission Experimental Study of Exospheric Hydrogen Atom Distributions by Lyman-alpha Detectors on the TWINS Mission

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa51a1607g&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SA51A-1607

Physics

[0328] Atmospheric Composition And Structure / Exosphere, [0394] Atmospheric Composition And Structure / Instruments And Techniques, [2794] Magnetospheric Physics / Instruments And Techniques

Scientific paper

Exospheric hydrogen (H) atoms resonantly scatter solar Lyman-alpha (121.6 nm) radiation, observed as the geocorona. Measurements of scattered solar photons allow one to probe time-varying three-dimensional distributions of exospheric H atoms. Knowledge of the exospheric properties is essential for the interpretation of magnetospheric images in energetic neutral atom (ENA) fluxes produced in charge exchange between energetic ions and H atoms. The Two Wide-angle Imaging Neutral Atom Spectrometers (TWINS) mission stereoscopically images the magnetosphere in ENA fluxes and additionally carries Lyman-alpha detectors (LADs) to investigate exospheric hydrogen. We use LAD measurements to obtain global H distributions on a daily basis. An 18-parameter expanded Bonn model is fit to observations during each 12-hour satellite orbit. As there are two TWINS instruments flying in widely spaced Molniya-type orbits, we have validated the approach by comparing independently derived distributions from two satellites. The experimental data is sensitive to H distributions from a radial distance of 3 to 6 Earth radii. The distributions reveal asymmetries from day to night, dawn to dusk, and north to south. We discuss the available data sets, their coverage, limitations, and promise for a study of exospheric response to variations in the solar output.

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