Preprints
https://doi.org/10.5194/angeo-2021-36
https://doi.org/10.5194/angeo-2021-36

  29 Jun 2021

29 Jun 2021

Review status: this preprint is currently under review for the journal ANGEO.

Terrestrial exospheric dayside H-density profile at 3–15 Re from UVIS/HDAC and TWINS Lyman-α data combined

Jochen Hard Zoennchen1, Hyunju Kim Connor2, Jaewoong Jung2, Uwe Nass1, and Hans Jörg Fahr1 Jochen Hard Zoennchen et al.
  • 1Argelander Institut für Astronomie, Astrophysics Department, University of Bonn, Auf dem Huegel 71, 53121 Bonn, Germany
  • 2Geophysical Institute, University of Alaska Fairbanks, Alaska, USA

Abstract. Terrestrial ecliptic dayside observations of the exospheric Lyman-α column intensity between 3–15 Earth radii (Re) by UVIS/HDAC at CASSINI have been analysed to derive the neutral exospheric H-density profile at the Earth's ecliptic dayside in this radial range. The data were measured during CASSINIS's swing by manoeuvre at the Earth on 18 August 1999 and are published by (Werner et al., 2004). In this study the dayside HDAC Lyman-α observations published by (Werner et al., 2004) are compared to calculated Lyman-α intensities based on the 3D H-density model derived from TWINS Lyman-α observations between 2008–2010 (Zoennchen et al., 2015). It was found, that both Lyman-α profiles show a very similar radial dependence in particular between 3–8 Re. Between 3.0–5.5 Re impact distance Lyman-α observations of both TWINS and UVIS/HDAC are existing at the ecliptic dayside. In this overlapping region the cross-calibration of the HDAC profile against the calculated TWINS profile was done, assuming, that the exosphere there was similar for both due to comparable space weather conditions. As result of the cross-calibration the conversion factor between counts/s and Rayleigh fc = 3.285 [counts/s/R] is determined for these HDAC observations. Using this factor the radial H-density profile for the Earths ecliptic dayside was derived from the UVIS/HDAC observations, which constrained the neutral H-density there at 10 Re to a value of 35 cm−3. Furthermore, a faster radial H-density decrease was found at distances above 8 Re (≈ r−3) compared to the lower distances 3–7 Re (≈ r2.37). This increased loss of neutral H above 8 Re might indicate a higher rate of H ionization in the vicinity of the magnetopause at 9–11 Re (near sub solar point) and beyond, because of increasing charge exchange interactions of exospheric H atoms with solar wind ions outside the magnetosphere.

Jochen Hard Zoennchen et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2021-36', J. D. Perez, 03 Aug 2021
  • RC2: 'Comment on angeo-2021-36', Anonymous Referee #2, 03 Oct 2021

Jochen Hard Zoennchen et al.

Jochen Hard Zoennchen et al.

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Short summary
Exospheric Ly-a observations of UVIS/HDAC at CASSINI on its Earth swing by and TWINS are used combined, to derive the exospheric H-density profile of the ecliptic dayside between 3–15 Re. At 10 Re nH = 35 cm−3 is found in the vicinity of the sub-solar point for quiet space weather conditions. Also a faster radial fall of the dayside H-density above 8 Re (r−3) compared to lower distances 3–7 Re (r−2.37) is found and possibly indicates enhanced loss of H-atoms near the magnetopause and beyond.