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Träfflista för sökning "WFRF:(Fujii S) ;pers:(Hirahara M.)"

Sökning: WFRF:(Fujii S) > Hirahara M.

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1.
  • Ogawa, Y., et al. (författare)
  • Coordinated EISCAT Svalbard radar and Reimei satellite observations of ion upflows and suprathermal ions
  • 2008
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:A5, s. A05306-
  • Tidskriftsartikel (refereegranskat)abstract
    • The relationship between bulk ion upflows and suprathermal ions was investigated using data simultaneously obtained from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Reimei satellite. Simultaneous observations were conducted in November 2005 and August 2006, and 14 conjunction data sets have been obtained at approximately 630 km in the dayside ionosphere. Suprathermal ions with energies of a few eV were present in the dayside cusp region, and the ion velocity distribution changed from an isotropic Maxwellian near the cusp region to tail heating at energies above a few eV in the cusp region. The velocity distribution of the suprathermal ions has a peak perpendicular or oblique to the geomagnetic field, and the temperature of the suprathermal ions was 0.9-1.4 eV. An increase in the phase space density (PSD) of the suprathermal ions, measured with the Reimei, was correlated with bulk ion upflow observed at the same altitude using EISCAT, and with the energy flux of precipitating electrons with energies of 50-500 eV. The PSD also has a good correlation with the electron temperature, which was increased by precipitation, but not with the ion temperature (0.1-0.3 eV) at the same altitude measured with EISCAT. These results suggest that plasma waves such as broadband extremely low frequency (BBELF) wavefields associated with precipitation are connected to the bulk ion upflows in the cusp and effectively cause the heating of suprathermal ions. The heating of suprathermal ions disagrees with anisotropic heating due to O+-O resonant charge exchange.
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2.
  • Ogawa, Y., et al. (författare)
  • On the source of the polar wind in the polar topside ionosphere : First results from the EISCAT Svalbard radar
  • 2009
  • Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:24, s. L24103-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present quantitative radar observations of both hydrogen ion (H+) and oxygen ion (O+) upflow in the topside polar ionosphere using measurements that were recently carried out with the EISCAT Svalbard Radar and the Reimei satellite. H+ upflow was clearly observed equatorward of the cusp above 500 km altitude. Within the cusp the H+ density was very low, and the upflow was dominated by O+ ions, but on closed field lines the H+ became the larger contributor to the upward flux above about 550 km. The total flux seemed to be conserved, and so below 550 km altitude O+ (with a small upward velocity of similar to 50 m s(-1)) appeared to determine the upward flux which was then maintained by H+! in the topside ionosphere. We also found that the H+ density in the topside polar ionosphere was several times higher than current predictions of ionospheric models like IRI2001.
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  • Resultat 1-2 av 2
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tidskriftsartikel (2)
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refereegranskat (2)
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Fujii, R. (2)
Hirahara, M. (2)Ta bort avgränsningen
Nozawa, S. (2)
Ogawa, Y (2)
Buchert, Stephan (1)
Buchert, Stephan C. (1)
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Asamura, K. (1)
Ebihara, Y. (1)
Häggström, I. (1)
Sandahl, I. (1)
Yamazaki, A (1)
Aso, T (1)
Oksavik, K. (1)
Sakanoi, T. (1)
Seki, K (1)
van Eyken, A P (1)
Obuchi, Y. (1)
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Uppsala universitet (2)
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Engelska (2)
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Naturvetenskap (2)

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