Thermospheric atomic hydrogen densities and fluxes from dayside Lyman /α measurements

Details Thermospheric atomic hydrogen densities and fluxes from dayside Lyman /α measurements Thermospheric atomic hydrogen densities and fluxes from dayside Lyman /α measurements

Mar 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jastp..63..331b&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 63, Issue 4, p. 331-340.

Physics

11

Scientific paper

Knowledge of the atomic hydrogen density profile ([H]/(z)) in the upper atmosphere is important both for studies of mesospheric-lower thermospheric (MLT) chemistry and for determining upper thermospheric-lower exospheric densities needed for realistic modeling of geocoronal density and ballistic flux distributions. Early work is reviewed and the sparseness of relevant data on the variation of [H] with altitude is emphasized. While optical measurements (e.g., of Lyman /α) constitute the most practical approach currently available, data analysis requires radiative transport (RT) modeling and [H]/(z) retrieval is effectively limited to obtaining values for a small number of modeling parameters. The key physical parameters of interest are the exobase density [H]c, the photochemically initiated upward flux /φ, and the density at the mesospheric peak [H]peak. This paper discusses RT-modeling analysis of dayside Lyman /α disk-to-limb scanning intensity /(4πI) measurements couched in terms of these parameters, aided by the use of a physically motivated parametric model for thermospheric [H]/(z) overcoming MSIS limitations at MLT altitudes. Illustrative sensitivity study results under solar maximum conditions are presented. The mesospheric density peak directly impacts /4πI profiles over a wide range of dayside solar zenith angles under such conditions. While mild difficulties in unraveling [H]peak and /φ in retrieval efforts may arise, analysis of dayside Lyman α4πI disk-to-limb scanning data expected from several future satellite FUV instruments should permit determination of [H]c and /φ over much of the dayside.

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