Global distribution of the He<sup>+</sup> column density observed by Extreme Ultra Violet Imager on the International Space Station

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  • Yuta Hozumi
    Graduate School of Science Kyoto University Kyoto Japan
  • Akinori Saito
    Graduate School of Science Kyoto University Kyoto Japan
  • Ichiro Yoshikawa
    Department of Complexity Science and Engineering University of Tokyo Tokyo Japan
  • Atsushi Yamazaki
    Institute of Space and Astronautical Science Japan Aerospace Exploration Agency Sagamihara Japan
  • Go Murakami
    Institute of Space and Astronautical Science Japan Aerospace Exploration Agency Sagamihara Japan
  • Kazuo Yoshioka
    Department of Earth and Planetary Science, Graduate School of Science University of Tokyo Tokyo Japan
  • Chia‐Hung Chen
    Department of Earth Sciences National Cheng Kung University Tainan Taiwan

書誌事項

公開日
2017-07
資源種別
journal article
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1002/2016ja023534
公開者
American Geophysical Union (AGU)

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説明

<jats:title>Abstract</jats:title><jats:p>The global distribution of He<jats:sup>+</jats:sup> in the topside ionosphere was investigated using data of the He<jats:sup>+</jats:sup> resonant scattering emission at 30.4 nm obtained by the Extreme Ultra Violet Imager (EUVI) onboard the International Space Station. The optical observation by EUVI from the low‐Earth orbit provides He<jats:sup>+</jats:sup> column density data above the altitude of 400 km, presenting a unique opportunity to study the He<jats:sup>+</jats:sup> distribution with a different perspective from that of past studies using data from in situ measurements. We analyzed data taken in 2013 and elucidated, for the first time, the seasonal, longitudinal, and latitudinal variations of the He<jats:sup>+</jats:sup> column density in the dusk sector. It was found that the He<jats:sup>+</jats:sup> column density in the winter hemisphere was about twice that in the summer hemisphere. In the December solstice season, the magnitude of this hemispheric asymmetry was large (small) in the longitudinal sector where the geomagnetic declination is eastward (westward). In the June solstice season, this relationship between the He<jats:sup>+</jats:sup> distribution and the geomagnetic declination is reversed. In the equinox seasons, the He<jats:sup>+</jats:sup> column densities in the two hemispheres are comparable at most longitudes. The seasonal and longitudinal dependence of the hemispheric asymmetry of the He<jats:sup>+</jats:sup> distribution was attributed to the geomagnetic meridional neutral wind in the <jats:italic>F</jats:italic> region ionosphere. The neutral wind effect on the He<jats:sup>+</jats:sup> distribution was examined with an empirical neutral wind model, and it was confirmed that the transport of ions in the topside ionosphere is predominantly affected by the <jats:italic>F</jats:italic> region neutral wind and the geomagnetic configuration.</jats:p>

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