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Author: search.filters.author.Tsugawa, TakuyaSubject: search.filters.subject.SEALION

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    Ionospheric peak height at the magnetic equator: Comparison between ionosonde measurements and IRI
    (2017-07-15)
    Maruyama, Takashi
    ;
    Ma, Guanyi
    ;
    Tsugawa, Takuya
    ;
    Supnithi, Pornchai
    ;
    Komolmis, Tharadol
    The ionospheric peak height in the F layer (hmF2) varies with not only thermospheric conditions but also dynamic processes in the upper atmosphere. At mid-latitudes, the field-aligned diffusion and recombination loss determine the hmF2 in the absence of applied vertical drift. Vertical drifts displace the hmF2 to a new equilibrium position in conjunction with the field-aligned redistribution of the plasma. In the vicinity of the magnetic equator, however, the equilibrium state would be different from low and mid-latitudes because the direct vertical coupling of plasma through the diffusion process is not allowed. Thus the behavior of hmF2 cannot be simply an extrapolation of that at low latitudes. In this paper, ionosonde measurements of the hmF2 near the magnetic equator and off-equatorial latitudes are compared with the IRI output.
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    Low-latitude ionospheric height variation as observed by meridional ionosonde chain: Formation of ionospheric ceiling over the magnetic equator
    (2014-01-01)
    Maruyama, Takashi
    ;
    Uemoto, Jyunpei
    ;
    Ishii, Mamoru
    ;
    Tsugawa, Takuya
    ;
    Supnithi, Pornchai
    A multipoint ionosonde observation campaign was conducted along the magnetic meridional plane in Southeast Asia to study ionosphere-thermosphere coupling. One station was near the magnetic equator and two of the other stations were at off-equatorial latitudes (∼10° magnetic latitude). The daytime ionospheric peak height (h<inf>m</inf>F<inf>2</inf>) was analyzed for each season during the solar minimum years, 2006-2007 and 2009. The peak height increased for ∼3 h after sunrise at the magnetic equator and off-equatorial latitudes, as expected from the daytime upward E × B drift. The apparent upward drift at the magnetic equator ceased before noon, while the drift at the off-equatorial latitudes continued upward and the layer height exceeded the equatorial height around noon. The noontime limited layer peak height at the magnetic equator, which was termed the ionospheric ceiling, did not depend on the season, while the maximum peak height at the off-equatorial latitudes largely varied with each season. Numerical modeling using the SAMI2 code was conducted and the features of the ionospheric ceiling were reproduced quite well. The dynamical parameters provided by the SAMI2 modeling runs showed that the ionospheric ceiling is formed by the field-aligned plasma diffusion, which is a part of the fountain effect. Key Points Multipoint ionosonde observation along the magnetic meridian in Southeast Asia Noontime restricted F layer peak height at the magnetic equator Revisiting the equatorial anomaly from the viewpoint of height variations