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Unusual ionospheric absorption characterizing energetic electron precipitation into the South Atlantic Magnetic Anomaly

Earth, Planets and Space volume 54, pages 907–916 (2002)Cite this article

Abstract

An imaging riometer (IRIS) was installed newly in the southern area of Brazil in order to investigate precipitation of energetic electrons into the South Atlantic Magnetic Anomaly (SAMA). An unusual ionospheric absorption event was observed in the nighttime (∼20 h LT) near the maximum depression (D st ∼ −164 nT) and the following positive excursion during the strong geomagnetic storm on September 22–23, 1999. The unusual absorption that has short time-duration of 30–40 min shows two characteristic features: One feature is a sheet structure of the absorption appearing at the high-latitude part of the IRIS field-of-view, showing an eastward drift from the western to the eastern parts and subsequent retreat to the western part. Another feature is a meridionally elongated structure with a narrow longitudinal width (100–150 km) appearing from the zenith to the low-latitude part of the IRIS field-of-view, enhanced simultaneously with the sheet absorption, and is subsequently changed to a localized structure. These features likely characterize precipitation of energetic electrons into the SAMA ionosphere, associated with substorm occurrences during the strong geomagnetic storm. From the eastward drift (∼250 m/s) of the sheet absorption, precipitating electrons are estimated to be ∼20 keV energies, assuming plasmaspheric electric fields of 1.8 mV/m. However, no ionospheric effect due to the precipitating electrons was definitely detected by the ionosonde measurements at Cachoeira Paulista, separated eastward by about 1000 km from the IRIS station.

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Authors and Affiliations

  1. Solar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa, 442-8507, Japan

    Masanori Nishino

  2. Basic Education Series, Physics, Takushoku University, Hachioji, Tokyo, 193-8585, Japan

    Kazuo Makita

  3. Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, 812-8581, Japan

    Kiyofumi Yumoto

  4. INPE, Sao Jose dos Campos, Sao Paulo, 12201-970, Brazil

    Fabiano S. Rodrigues & Mangalathayil A. Abdu

  5. Southern Space Research Center, INPE, Rio Grade de Sul, 97119-900, Brazil

    Nelson J. Schuch

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  1. Masanori Nishino
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  2. Kazuo Makita
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  3. Kiyofumi Yumoto
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  4. Fabiano S. Rodrigues
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  6. Mangalathayil A. Abdu
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Correspondence to Masanori Nishino.

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Nishino, M., Makita, K., Yumoto, K. et al. Unusual ionospheric absorption characterizing energetic electron precipitation into the South Atlantic Magnetic Anomaly. Earth Planet Sp 54, 907–916 (2002). https://doi.org/10.1186/BF03352438

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  • DOI: https://doi.org/10.1186/BF03352438

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