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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 29, issue 12 | Copyright
Ann. Geophys., 29, 2211-2217, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 01 Dec 2011

Regular paper | 01 Dec 2011

The TWINS exospheric neutral H-density distribution under solar minimum conditions

J. H. Zoennchen1, J. J. Bailey2, U. Nass1, M. Gruntman2, H. J. Fahr1, and J. Goldstein3,4 J. H. Zoennchen et al.
  • 1Argelander Institut für Astronomie, Astrophysics Department, University of Bonn, Auf dem Huegel 71, 53121 Bonn, Germany
  • 2University of Southern California, Department of Astronautical Engineering, Viterbi School of Engineering, Los Angeles, CA 90089-1192, USA
  • 3Southwest Research Institute, San Antonio, TX, USA
  • 4University of Texas, San Antonio, San Antonio, TX, USA

Abstract. Terrestrial exospheric atomic hydrogen (H) resonantly scatters solar Lyman-α (121.567 nm) radiation, observed as the glow of the H-geocorona. The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) satellites are equiped with two Lyman-α line-of-sight Detectors (LADs) each. Since during the past solar minimum conditions the relevant solar control parameters practically did not vary, we are using LAD data between June and September 2008 to create a time averaged hydrogen geocorona model representative for these solar minimum conditions. In this averaged model we assume that the H-geocorona is longitudinally symmetric with respect to the earth-sun line. We find a 3-dimensional H-density distribution in the range from 3 to 8 earth radii which with some caution can also be extrapolated to larger distances. For lower geocentric distances than 3 earth radii a best fitting r-dependent Chamberlain (1963)-like model is adapted. Main findings are larger than conventionally expected H-densities at heights above 5 RE and a pronounced day-to-night side H-density asymmetry. The H-geocorona presented here should serve as a reference H-atmosphere for the earth during solar minimum conditions.

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