The spatial distribution of hydrogen ions at topside ionosphere in local daytime

  • Author(s): Xuhui Shen and Xuemin Zhang
  • DOI: 10.3319/TAO.2017.06.30.01
  • Keywords: Hydrogen ion, Topside ionosphere, Seasonal asymmetry, DEMETER satellite
  • Peak H+ ions occur at winter hemisphere in topside ionosphere in local daytime
  • Solstitial asymmetry in H+ is enhanced at DEMETER altitude
  • The transition height reduces quickly at 10-20°N in solar minimum
Abstract

Using DEMETER and DMSP satellite data, the spatial distribution of hydrogen ion (H+) in local daytime has been compared and analyzed. At 840 km of DMSP height, the seasonal variations of H+ density is basically symmetric, with similar den­sity values near to the magnetic equator at northern hemisphere in December and at southern hemisphere in June. But at DEMETER satellite height, the peak H+ density shows obvious enhancement at northern hemisphere in December solstice, while with approximate small values at both hemispheres in June. This spatial distribution fea­ture is totally different with other ions such as O+ and He+ at the topside ionosphere. And also it influences the transition height in topside ionosphere, with lower transi­tion height over northern hemisphere in December season at 10 - 20°N than those at equator and over southern hemisphere in June season. The solstitial asymmetry AI of H+ at 670 km altitude gives the significant December season enhancement over northern hemisphere, which is typically reversed with Ne and Ni with large numbers over southern hemisphere in December season. Finally combining with the distribu­tion of H atoms and neutral wind velocity in upper atmosphere, the forming mecha­nism and asymmetry feature of peak H+ density is discussed. It is illustrated that the upwelling movement at equatorial area and northward neutral wind play important roles in H+ peak drift in December season at DEMETER satellite altitude below the transition height where H+ is not the main composition in the local daytime in solar minimum years.

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