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

Candido, Claudia M. N.; Shi, Jiankui; Batista, Inez S.; Becker-Guedes, Fabio; Correia, Emília; Abdu, Mangalathayil A.; Makela, Jonathan; Balan, Nanan; Chapagain, Narayan; Wang, Chi; Liu, Zhengkuan

We present a case study of unusual spread-F structures observed by ionosondes at two equatorial and low-latitude Brazilian stations – São Luís (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 postmidnight hours of moderate solar activity (F10.7 < 97 sfu, where 1 sfu = 10−22 W m−2 s−1) 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 the 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–Pérot interferometer (FPI) installed at CZ and discuss its possible role in the development of the irregularities.

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Candido, Claudia M. N. / Shi, Jiankui / Batista, Inez S. / et al: Postmidnight equatorial plasma irregularities on the June solstice during low solar activity – a case study. 2019. Copernicus Publications.

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Rechteinhaber: Claudia M. N. Candido et al.

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