Absence of High Frequency Echoes From Ionosondes During the 23–25 April 2023 Geomagnetic Storm; What Happened?

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dc.contributor.authorHabarulema, John Bosco
dc.contributor.authorZhang, Yongliang
dc.contributor.authorMatamba, Tshimangadzo
dc.contributor.authorLu, Gang
dc.contributor.authorKatamzi‐Joseph, Zama
dc.contributor.authorFagundes, Paulo Roberto
dc.contributor.authorOkoh, Daniel
dc.contributor.authorSeemala, Gopi
dc.date.accessioned2025-01-29T19:41:47Z
dc.date.available2025-01-29T19:41:47Z
dc.date.issued22024
dc.description.abstractWe report an unusual event on absence of high frequency (HF) echoes in ionosonde observations from the ionospheric F2 region during the geomagnetic storm of 23–25 April 2023. This event was observed in both southern and northern hemispheres over two stations, Grahamstown (33.3°S, 26.5°E), South Africa and Pruhonice (50.0°N, 14.6°E), Czech Republic. Significant O/N2 depletion over the stations was observed by TIMED/GUVI, indicating a strong negative ionospheric storm. This is unique since absence of echoes in ionosonde measurements is usually due to strong radio absorption in the ionosphere associated with solar flares. However, there was no flare activity during the periods of “absent” F2 HF echoes. On the other hand, the ionosonde detected echoes from E‐layer. TIEGCM simulation reproduced TIMED/GUVI O/N2 depletion and showed that NmE was larger than NmF2 on dayside over Pruhonice. TIMED/GUVI O/N2 also showed a clear spatial gradient in the O/N2 depleted regions, suggesting F‐region ionosphere was tilted. By estimating the critical frequency of the F2 layer using GNSS observations, we have shown that it wasn't possible for the ionospheric electron density to reach depletion levels prohibiting reflection of HF echoes from ionosondes. We suggest that this phenomena may have been caused by either (a) maximum electron density of E layer exceeding that of F2 layer and/or (b) ionospheric tilting which made the signals to be reflected far away from the ionosonde locations.
dc.description.physical13 p.
dc.format.mimetypePDF
dc.identifier.affiliationUniversidade do Vale do Paraíba
dc.identifier.affiliationRhodes University
dc.identifier.affiliationSouth African National Space Agency
dc.identifier.affiliationNorth‐West University
dc.identifier.affiliationJohns Hopkins University
dc.identifier.affiliationInstitute of Atmospheric Physics
dc.identifier.affiliationNational Center for Atmospheric Research
dc.identifier.affiliationCentre for Space Science and Technology Education
dc.identifier.affiliationIstituto Nazionale Geofisica e Vulcanologia
dc.identifier.affiliationIndian Institute of Geomagnetism
dc.identifier.bibliographicCitationHabarulema, J. B. et al. Absence of high frequency echoes from ionosondes during the 23–25 April 2023 geomagnetic storm; what happened? Journal of Geophysical Research: Space Physics. [s.l.], v. 129, n. 3, p. 1-13, 2024.
dc.identifier.doi10.1029/2023JA032277
dc.identifier.urihttps://repositorio.univap.br/handle/123456789/530
dc.language.isoen_US
dc.publisherAdvancing Earth and Space Sciences
dc.rights.holderJohn Bosco Habarulema
dc.rights.holderYongliang Zhang
dc.rights.holderTshimangadzo Matamba
dc.rights.holderGang Lu
dc.rights.holderZama Katamzi‐Joseph
dc.rights.holderPaulo Roberto Fagundes
dc.rights.holderDaniel Okoh
dc.rights.holderGopi Seemala
dc.subject.keywordGeomagnetic Storm
dc.subject.keywordElectron density
dc.titleAbsence of High Frequency Echoes From Ionosondes During the 23–25 April 2023 Geomagnetic Storm; What Happened?
dc.typeArtigos de Periódicos

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