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Abstract. Based on Ly-α-line-of-sight measurements taken with two Ly-α detectors onboard of the satellite TWINS1 (Two Wide-angle Imaging Neutral-atom Spectrometers) density profiles of the exospheric, neutral geocoronal hydrogen were derived for the time period between summer solstice and fall equinox 2008. With the help of specifically developed inversion programs from Ly-α line of sight intensities the three-dimensional density structure of the geocoronal hydrogen at geocentric distances r > 3 R E could be derived for the period mentioned characterized by very low solar 10.7 cm radiofluxes of ≈65-70 [10 −22 W m −2 Hz −1 ]. The time-variable, solar "line-centered"-Ly-α-flux was extracted on the basis of daily (terrestrial) NGDC 10.7 cm radioflux data using the models from Barth et al. (1990) and VidalMadjar (1975).The results for the geocoronal H-densities are compared here both with theoretical calculations based on a MonteCarlo model by Hodges (1994) and with density profiles obtained with the Geocoronal Imager (GEO) by Østgaard and Mende (2003). In our results we find a remarkably more pronounced day-/night-side asymmetry which clearly hints to the existence of a hydrogen geotail (i.e. a tail structure with comparatively higher hydrogen densities on the night side of the earth for geocenctric distances >4 R E ), and a only weakly pronounced polar depletion. These unexpected features we try to explain by new models in the near future. The derived 3-D-H-density structures are able to explain the line-of-sight (LOS) dependent Ly-α intensity variations for all LOS seen up to now with TWINS-LAD. The presented results are valid for the region with geocentric distances 3 R E < r < 7 R E and are based on the reasonable assumption of an optically thin H-exosphere with respect to resonant Ly-α-scattering allowing the use of single scattering calculations.

The TWINS project (Two Wide-angle Imaging Neutral-atom Spectrometers) is mainly devoted to measure high energy neutral atoms (ENAs) originating via charge exchange of protons with geocoronal hydrogen atoms in the plasmasphere and magnetosphere. In order to unfold the local ion density along the line-of-sight (LOS) from the integrated ENA flux measurements, a good knowledge of the geocoronal hydrogen density distribution is needed. Therefore, two Lyman-α detectors (LADs)-designed and calibrated by the authors-were added to the TWINS package. These detectors register line-integrated Lyman-α resonance emission intensities which then can be used to get the actual local hydrogen densities with the help of a numerical inversion routine.

Abstract. We start our considerations from two more recent findings in heliospheric physics: One is the fact that the primary solar wind protons do not cool off adiabatically with distance, but appear to be heated. The other one is that secondary protons, embedded in the solar wind as pick-up ions, behave quasi-isothermal at their motion to the outer heliosphere. These two phenomena must be physically closely connected with each other. To demonstrate this we solve a coupled set of enthalpy flow conservation equations for the two-fluid solar wind system consisting of primary and secondary protons. The coupling of these equations comes by the heat sources that are relevant, namely the dissipation of MHD turbulence power to the respective protons at the relevant dissipation scales. Hereby we consider both the dissipation of convected turbulences and the dissipation of turbulences locally driven by the injection of new pick-up ions into an unstable mode of the ion distribution function. Conversion of free kinetic energy of freshly injected secondary ions into turbulence power is finally followed by partial reabsorption of this energy both by primary and secondary ions. We show solutions of simultaneous integrations of the coupled set of differential thermodynamic two-fluid equations and can draw interesting conclusions from the solutions obtained. We can show that the secondary proton temperature with increasing radial distance asymptotically attains a constant value with a magnitude essentially determined by the actual solar wind velocity. Furthermore, we study the primary proton temperature within this two-fluid context and find a polytropic behaviour with radially and latitudinally variable polytropic indices determined by the local heat sources due to dissipated turbulent wave energy. Considering latitudinally variable solar wind conditions, as published by McComas et al. (2000), we also predict latitudinal variations of primary proton temperatures at large solar distances.

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