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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 28 Nov 2018

Regular paper | 28 Nov 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Postmidnight equatorial plasma irregularities on June solstice during low solar activity – a case study

Claudia M. N. Candido1,2, Jiankui Shi1, Inez S. Batista2, Fabio Becker-Guedes2, Emília Correia2,6, Mangalathaiyl A. Abdu2,4, Jonathan Makela3, Nanan Balan7, Narayan Chapagain5, Chi Wang1, and Zhengkuan Liu1 Claudia M. N. Candido et al.
  • 1National Space Science Center, NSSC, Chinese Academy of Sciences, State Key Laboratory, China-Brazil Joint Laboratory for Space Weather, China
  • 2National Institute for Space Research – INPE, São José dos Campos, SP, Brazil
  • 3Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
  • 4Instituto Tecnológico de Aeronáutica – ITA – São Jose dos Campos, Brazil
  • 5Departament of Physics, Patan Multiple Campus, Tribhuvan University, Latitpur, Nepal
  • 6Centro de Radio Astronomia e Astrofísica Mackenzie, CRAAM, University Presbiteriana Mackenzie – São Paulo – Brazil
  • 7Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Abstract. We present a case study of unusual spread-F structures observed by ionosondes at two equatorial and low latitude Brazilian stations – Sao Luis (SL: 44.2° W, 2.33° S, dip angle: −6.9°) and Fortaleza (FZ: 38.45° W, 3.9° S, dip angle: −16°). The irregularity structures observed from midnight to post-midnight hours of moderate solar activity (F10.7 < 97) have characteristics different from typical post-sunset equatorial spread-F. The spread-F traces first appeared at or above the F-layer peak and gradually became well-formed mixed spread-F. They also appeared as plasma depletions in the 630.0 nm airglow emissions made by a wide-angle imager located at nearby low latitude station Cajazeiras (CZ: 38.56° W, 6.87° S, dip angle: −21.4°). The irregularities appeared first over FZ and later over SL, giving evidence of an unusual westward propagation or a horizontal plasma advection. The drift mode operation available in one of the ionosondes (a Digital Portable Sounder, DPS-4) has enabled us to analyze the horizontal drift velocities and directions of the irregularity movement. We also analyzed the neutral wind velocity measured by a Fabry-Perot interferometer (FPI) installed at CZ and discussed its possible role on the development of the irregularities.

Claudia M. N. Candido et al.
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Claudia M. N. Candido et al.
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Short summary
This study is concerning of the postmidnight ionospheric irregularities observed during low solar activity conditions. We analyze data from digisondes and optical imaging systems located at equatorial region over Brazil. The results show that they occur under unfavorable and unexpected conditions. This work can be useful for Space Weather forecasting during low solar activity.
This study is concerning of the postmidnight ionospheric irregularities observed during low...