O. S. Bolaji

Petrozavodsk State University

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A. B. Rabiu

Obafemi Awolowo University

J.O. Adeniyi

University of Ilorin

E.O. Oyeyemi

University of Lagos

B.O. Adebesin

Landmark University

J. B. Fashae

Bowen University

S. J. Adebiyi

Redeemer's University

Daniel Okoh

National Space Research and Development Agency

S.O. Ikubanni

Landmark University

R. O. Kaka

Virginia Tech

E.O. Falayi

Tai Solarin University of Education

Cooperative Institutions

University of Lagos

National Space Research and Development Agency

Federal University of Technology

Chinese Academy of Sciences

Obafemi Awolowo University

National Institute for Space Research

The Abdus Salam International Centre for Theoretical Physics (ICTP)

University of Ilorin

Universidade do Vale do Paraíba

University of Science and Technology of China

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Response of the American equatorial ionization anomaly to 2016 Arctic sudden stratospheric warming events

Frontiers in Astronomy and Space Sciences (2022)

O. R. Idolor A.O. Akala O. S. Bolaji E.O. Oyeyemi Alaba Tolulope Agbele

Apart from the rapid ionospheric response to geomagnetic forcing originating from the Sun during extreme space weather events, forcing from the lower atmosphere below still exerts a significant influence on the ionosphere during quiet-time conditions. This study examines the ionospheric response of the equatorial ionization anomaly (EIA) in the American sector to the combined influence of the cascades of sudden stratospheric warming (SSW) events and the geomagnetic storms that coexisted with them during the period of January–March 2016. We adopted a multi-instrument and multi-modeling approach with the study locations spanning ±40° geomagnetic latitudes. Our results showed a hemispheric asymmetry in the total electron content and change in total electron content (ΔTEC) distribution with higher enhancement clearly visible in the Northern Hemisphere in comparison to the Southern Hemisphere (NH). Semidiurnal signatures were observed in both ΔTEC and equatorial electrojet parameters for some days. The double-peak zonal mean zonal wind amplitude days supported the formation of the reverse fountain effects. The different SSW peak temperature days also showed either positive or negative ionospheric response. Generally, orientation of the prompt penetration electric field (PPEF) and their strengths at either daytime or nighttime played a weak role in the ionosphere response during some of the geomagnetic storms. The negative and positive ionospheric responses under geomagnetic storm conditions were ascribed to changes in the composition of the thermosphere, prompt penetration electric field (PPEF), and traveling atmospheric disturbances (TADs).

Sudden stratospheric warming

10.3389/fspas.2022.1024607

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Ionospheric Current Variations Induced by the Solar Flares of 6 and 10 September 2017

Space Weather (2020)

Charles Owolabi Jiuhou Lei O. S. Bolaji Dexin Ren Akimasa Yoshikawa

Abstract We examine the global ionospheric current in relation to X9.33 disk and X8.28 limb flares, which had significant differences in their solar X‐ray and extreme ultraviolet (EUV) fluxes using the ground‐based magnetometer data. At the peak of X9.33 flare, when X‐ray and EUV radiations were significantly enhanced, the northern current vortex was situated at (40°N, 12 LT), while the southern current vortex was found at (30°S, 13LT). In comparison to the X8.28 flare, the northern current vortex was seen at (16°N, 12LT), while the southern current vortex was situated at (35°S, 14LT), which was 2 hr earlier in local time compared to those observed in the X9.33 flare. The changes in the total current intensity of the X9.33 flare is about 16% less than that of the X8.28 flare, thus revealing that the current variations relative to both flares are due to solar flux and universal time variations. The daytime X9.33 flare northern current vortex is stronger, while the southern vortex is less intense than the corresponding vortex of X8.28 flare. Even though both flares happened in equinox, the current vortices are nearly symmetric. There were significant hemispheric changes in the focus position leading to the hemispheric asymmetry. Our results indicated that both the enhanced X‐ray and EUV fluxes during flares could have impacts on the ionospheric electric field and current, but their relative contributions and the underlying physics need further investigations.

Flare

Solar flare

Current sheet

10.1029/2020sw002608

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Citations (16)

Total electron content and magnetic field intensity over Ilorin, Nigeria

Journal of Atmospheric and Solar-Terrestrial Physics (2013)

O. S. Bolaji J.O. Adeniyi I. A. Adimula S. M. Radicella Patricia H. Doherty

Noon

Sunrise

Sunset

Trough (economics)

10.1016/j.jastp.2013.02.011

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Citations (20)

Climatology of the inter-hemispheric field-aligned currents system over the Nigeria ionosphere

Journal of Atmospheric and Solar-Terrestrial Physics (2012)

O. S. Bolaji A. B. Rabiu E.O. Oyeyemi K. Yumoto

Noon

Dusk

10.1016/j.jastp.2012.07.008

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Citations (12)

First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All‐Sky Airglow Imager and GNSS Receivers

Journal of Geophysical Research Space Physics (2017)

Daniel Okoh A. B. Rabiu K. Shiokawa Y. Otsuka O. S. Bolaji

Abstract This is the first paper that reports the occurrence frequency of equatorial plasma bubbles and their dependences of local time, season, and geomagnetic activity based on airglow imaging observations at West Africa. The all‐sky imager, situated in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S), has a 180° fisheye view covering almost the entire airspace of Nigeria. Plasma bubbles are observed for 70 nights of the 147 clear‐sky nights from 9 June 2015 to 31 January 2017. Differences between nighttime and daytime ROTIs were also computed as a proxy of plasma bubbles using Global Navigation Satellite Systems (GNSS) receivers within the coverage of the all‐sky imager. Most plasma bubble occurrences are found during equinoxes and least occurrences during solstices. The occurrence rate of plasma bubbles was highest around local midnight and lower for hours farther away. Most of the postmidnight plasma bubbles were observed around the months of December to March, a period that coincides with the harmattan period in Nigeria. The on/off status of plasma bubble in airglow and GNSS observations were in agreement for 67.2% of the total 768 h, while we suggest several reasons responsible for the remaining 32.8% when the airglow and GNSS bubble status are inconsistent. A majority of the plasma bubbles were observed under relatively quiet geomagnetic conditions ( Dst ≥ −40 and Kp ≤ 3), but there was no significant pattern observed in the occurrence rate of plasma bubbles as a function of geomagnetic activity. We suggest that geomagnetic activities could have either suppressed or promoted the occurrence of plasma bubbles.

Airglow

Solstice

Local time

10.1002/2017ja024602

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Citations (24)

Response of the Ionospheric TEC to SSW and Associated Geomagnetic Storm Over the American Low Latitudinal Sector

Space Weather (2022)

J. B. Fashae O. S. Bolaji A. B. Rabiu

Abstract During the sudden stratospheric warming (SSW) event in 2013, we investigated the American low latitude around 75°W. We used 12 Global Positioning System (GPS) receivers, a pair of magnetometers, and the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite airglow instrument to unveil the total electron content (TEC), inferred vertical drift, and the changes in the neutral composition, respectively. A major SSW characterized the 2013 SSW event with the main phase (7–27 January 2013) overlapped by a minor geomagnetic storm (17 January 2013). The late morning inferred downward‐directed E X B drift did not support the varying equatorial ionization anomaly (EIA) signature during the SSW onset (7 January 2013). The mid‐January (15–16 January 2013) witnessed enhancement in the varying inferred upward‐directed E X B drift at both hemispheres. On 17 January 2013, there were reductions in the varying inferred upward‐directed E X B drift at both hemispheres. Generally, the SSW effect on TEC around 15–16 January 2013 is more pronounced than the SSW onset. During the mid‐January (15–16 January 2013), the higher northern EIA crests are facilitated majorly by the SSW compared to the photo‐ionization that primarily enabled the southern crests. On 17 January 2013, the combined effect of photo‐ionization and SSW contribution was majorly responsible for the slight reduction in the northern crest. In the southern hemisphere, photo‐ionization played the lead role as the SSW, and the minor geomagnetic storm roles are secondary in enhancing the southern crest.

10.1029/2021sw002999

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Investigation on the Variability of the Geomagnetic Daily Current During Sudden Stratospheric Warmings

Journal of Geophysical Research Space Physics (2019)

Charles Owolabi Jiuhou Lei O. S. Bolaji Oluwaseyi Jimoh Haibing Ruan

Abstract The magnetic field records of the magnetometer networks in the American, East Asian‐Australian, and European‐African sectors were employed in this present work. We used them to investigate equatorial electrojet (EEJ), counter electrojet (CEJ), tidal variability in EEJ strength and ionospheric current during the 2005 / 2006 and 2008 / 2009 sudden stratospheric warming (SSW) events. In addition to the well‐investigated tidal variability in EEJ strength over the American and East Asian sectors, we investigated that of the African sector for the first time. Interestingly, the tidal components in EEJ strength during both SSW events clearly exhibit marked longitudinal differences with high, moderate, and low amplitudes in the American, East Asian, and African sectors, respectively. An exception found around day 71 in the African sector after the 2008 / 2009 SSW event had higher solar diurnal tidal component as compared to that of the Asian sector. Over the American sector, solar and lunar semidiurnal tides were strongly associated with CEJ current during both SSW events, whereas at the African and East Asian sectors such variabilities are not evident. A solar diurnal tidal component was strongly related to a reduction in the EEJ strength over the East Asian sector. In addition, a prolonged period of CEJ occurrence that begins during the SSW precondition and ends when the SSW was evolving characterized the African sector during both SSW events. There is a steady shift in phase at later hours when both SSW events are evolving.

Equatorial electrojet

10.1029/2019ja026667

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Citations (11)

St. Patrick's Day Storms and GPS-TEC Response at Some African Low-Latitude Stations (Abstract only)

S.O. Ikubanni S. J. Adebiyi B.O. Adebesin B.W. Joshua O. S. Bolaji

The 2015 St. Patrick’s Day storm, which is one of the most intense geomagnetic storm in this present solar cycle (SYM-H = -213nT), as well as the similar event in 2013 (SYM-H = -132nT). We investigated the response of the Total Electron Content (TEC) derived from four (4) Global Positioning System (GPS) measurements in African low latitude region during these two (2) events. Analysis of the TEC data revealed larger magnitude disturbed time variation from quiet-time average behavior in 2015 than 2013, while the deviation is larger during the recovery phase than the main phase for both storm events. There was TEC enhancements at Libreville (NKLG) during the minimum depression of SYM-H and at Malindi (MAL2) and Lusaka (ZAMB) during the prenoon periods of the first day of the recovery phase. The enhancement episodes dominates at the equatorial stations while depletion episodes dominates at the low latitude station during the 2013 recovery phase. In 2015, depletion episodes occurred during the minimum downward excursion period, the postnoon and postsunset periods of the first recovery day at the equatorial stations and enhancement episodes observed at the prenoon. Negative storm phases dominates the remaining recovery days in the low latitude stations of MBAR and MAL2, extending for about 36 hours, particularly around the midday, post-sunset and midnight. Comparison with observations from other works revealed distinct responses at different sectors.

Sunset

Low latitude

Midnight

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Ionospheric climatology at Africa EIA trough stations during descending phase of sunspot cycle 22

Journal of Atmospheric and Solar-Terrestrial Physics (2018)

B.O. Adebesin A. B. Rabiu O. S. Bolaji J.O. Adeniyi Christine Amory‐Mazaudier

Sunspot

Trough (economics)

Solar cycle 24

Noon

Solar maximum

10.1016/j.jastp.2018.03.009

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Citations (16)

Investigation of the Variability of Night‐Time Equatorial Thermospheric Winds Over Nigeria, West Africa

Journal of Geophysical Research Space Physics (2021)

A. B. Rabiu Daniel Okoh Qian Wu O. S. Bolaji R. B. Abdulrahim

Abstract This study examined the variability of the night‐time equatorial thermospheric meridional and zonal wind speeds using an optical Fabry‐Perot interferometer (FPI) located in Abuja, Nigeria (Geographic: 8.99°N, 7.39°E; Geomagnetic latitude: −1.60). The study period covered 9 months with useable data of 139 nights between March 2016 and January 2018. The hourly zonal wind speed is between −124 and 163 ms −1 and that of the meridional wind ranged between −70 and 95 ms −1 . Comparison of FPI ground‐based measurements with estimates from the Horizontal Wind Model (HWM‐14) accurately reproduced the post‐midnight meridional component, but for some departure of ∼50 ms −1 during pre‐midnight. A very good agreement is observed between the predicted and measured zonal winds speed in the month of January 2018. However, the HWM‐14 more often underestimated the zonal wind speeds in the months of 2016. Hence, this necessitates a call for improvement of the HWM‐14 by using newly observed data in order to better characterize the West African sector. The varying zonal winds showed modal periods of 25.9 and 133.5 days, which are quasi 27 days and quasiterannual periodic variations, respectively. On the meridional wind, oscillatory periods of 133.5 and 23.1 days are seen in year 2016 and 2017, respectively.

Prevailing winds

Middle latitudes

Meridional flow

10.1029/2020ja028528

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Citations (8)