JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM11] [EE] Mesosphere-Thermosphere-Ionosphere Coupling in the Earth's Atmosphere

Wed. May 24, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)

convener:Loren Chang(Institute of Space Science, National Central University), Huixin Liu(Earth and Planetary Science Division, Kyushu University SERC, Kyushu University), Akinori Saito(Department of Geophysics, Graduate School of Science, Kyoto University), Tzu-Wei Fang

[PEM11-P09] Seasonal and spatial variation of He+ column density in the evening topside ionosphere observed by ISS-IMAP/EUVI

*Yuta Hozumi1, Akinori Saito2, Ichiro Yoshikawa3, Atsushi Yamazaki4, Go Murakami4, Kazuo Yoshioka3 (1.University of Electro-Communications, 2.Kyoto Univ., 3.The University of Tokyo, 4.Institute of Space and Astronautical Science / Japan Aerospace Exploration Agency)

The seasonal, longitudinal and latitudinal variations of He+ distribution in the evening topside ionosphere in 2013 - 2015 are elucidated with data of He+ resonant scattering obtained by Extreme Ultra Violet Imager (EUVI) onboard the International Space Station (ISS). EUVI provides a data set of the column density of He+ in the topside ionosphere. The data set provides a unique opportunity to study He+ distribution in the topside ionosphere from a different perspective of past studies using in-situ measurement data. During the solstice seasons, an enhancement of He+ column density in the winter hemisphere is observed. The magnitude of this hemispheric asymmetry shows a longitudinal variability. Around the June solstice, the hemispheric asymmetry was greater in the longitude sector where the geomagnetic declination angle is negative and smaller in the longitude sector where the geomagnetic declination angle is positive. Around the December solstice, on the other hand, this longitudinal variation of the asymmetry magnitude had opposite tendency. The hemispheric asymmetry of the effective neutral wind well explains this behavior of He+. The field-aligned component of neutral wind in the F-region is varied in longitude under the presence of finite geomagnetic declination angle and large zonal wind. We examined the seasonal and longitudinal variation of the effective wind with HWM14 model. In the equinox seasons, two longitudinal maxima were observed at around 140ºE and 30ºE. The longitudinal variation of the effective neutral wind is a candidate of these two maxima of He+ concentration. These results suggest that the transport of ions in the topside ionosphere is strongly affected by the F-region neutral wind.