Neutral winds and tides over South Africa

Ojo, Taiwo Theophilus

Title: Neutral winds and tides over South Africa
Creator: Ojo, Taiwo Theophilus
Subject: Atmospheric tides
Subject: Ionosondes
Subject: Fabry-Perot interferometers
Subject: Thermospheric winds
Subject: Servomechanisms
Subject: Climatology
Subject: ‎Neutral winds
Subject: Horizontal Wind Model (HWM)‎
Date Issued: 2022-04-08
Date: 2022-04-08
Type: Doctoral thesis
Type: text
Identifier: http://hdl.handle.net/10962/232459
Identifier: vital:49993
Identifier: DOI 10.21504/10962/232459
Description: This thesis presents the first results of a climatology of nighttime thermospheric neutral winds between February 2018 and January 2019 measured by a Fabry-Perot interferometer (FPI) in Sutherland, South Africa (32.2°S, 20.48°E; geomagnetic latitude: 40.7°S). This FPI measures the nighttime oxygen airglow emission at 630.0 nm, which has a peak intensity at an altitude of roughly 250 km. The performance of the Horizontal Wind Model (HWM14) was evaluated by comparing results from HWM14 with the FPI measurements. The results showed that the model had a better agreement with the measurements for meridional component compared to the zonal component. In addition, the HWM14 zonal wind consistently peaked several hours (~3 h) prior to the measured wind, creating what looks like a phase shift compared to the measured wind. An investigation of this apparent phase shift revealed it to be a consequence of a difference in phase shift of the terdiunal tide. Since ionosondes are more prolific with wider temporal and spatial coverage than FPIs, nighttime meridional winds aligned to the magnetic meridian were inferred from the peak height (hmF2) of ionospheric data taken from South Africa ionosonde network using the servo model during February 2018-June 2019. These were compared with FPI measured meridional wind and benchmarked with HWM14 and Magnetic mEridional NeuTrAl Thermospheric (MENTAT) model. The amplitudes and trends of the calculated meridional winds across all four ionosonde stations agreed relatively well with the observed data, especially during the summer months. Furthermore, the results confirmed that the ionosonde station located closest to the FPI, i.e. Hermanus station, had better agreement with measurements compared to the stations located at further distances. The extraction and analysis of atmospheric tides, namely the diurnal, semidiurnal, terdiurnal and 6-hour components from the FPI as well as the long-term tidal winds variations from the thermospheric wind measurements were investigated. The results showed that the semidiurnal peak mostly had the highest peak across all the months, indicating that the semidiurnal tides dominate the dynamic structure of the upper mesosphere at midlatitudes, consistent with previous observation over midlatitudes. Futhermore, the signature of the diurnal tide in the meridional (zonal) wind was stronger in winter (summer) and weaker in summer (winter). Also, semidiurnal tide didn't show any trend with season, while the terdiurnal tide was dominant in summer (zonal) and winter (meridional). Lastly, the 6 hour tide was detected intermittently during the period of the study and had the weakest signature (i.e. lowest amplitudes).
Description: Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
Format: computer
Format: online resource
Format: application/pdf
Format: 1 online resource (110 pages)
Format: pdf
Publisher: Rhodes University
Publisher: Faculty of Science, Physics and Electronics
Language: English
Rights: Ojo, Taiwo Theophilus
Rights: Use of this resource is governed by the terms and conditions of the Creative Commons "Attribution-NonCommercial-ShareAlike" License (http://creativecommons.org/licenses/by-nc-sa/2.0/)

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