Isaac Abiodun Adimula
@unilorin.edu.ng
Professor, Department of Physics
University of Ilorin
RESEARCH, TEACHING, or OTHER INTERESTS
Physics and Astronomy, Atmospheric Science, Earth and Planetary Sciences, Electrical and Electronic Engineering
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Mumin Olatunji Oladipo, Abiodun Isaac Adimula, Adeniji Olawepo, Saeed Abioye Bello, and Benjamin Wisdom Joshua
Elsevier BV
O.A. Oladipo, A.O. Olawepo, J.O. Adeniyi, I.A. Adimula, A.A. Willoughby, and P.H. Doherty
Elsevier BV
O.A. Oladipo, A.O. Olawepo, J.O. Adeniyi, I.A. Adimula, A.A. Willoughby, and P.H. Doherty
Elsevier BV
A. O. Olawepo, O. A. Oladipo, S. Sodiq, O. Odeyemi, B. W. Joshua, S. J. Adebiyi, J. O. Adeniyi, and I. A. Adimula
Pleiades Publishing Ltd
B. O. Adebesin, J. O. Adeniyi, I. A. Adimula, S. J. Adebiyi, S. O. Ikubanni, and B. J. Adekoya
Nigerian Society of Physical Sciences
A short review of the pattern and morphology of the equatorial plasma drift velocities, particularly during the evening-time Pre-reversal enhancement (PRE) period in the African region had been presented. The seasonal PRE peak values across some locations in the West-African region were considered and compared with other sectors of the world. While most plasma drift observations in the African region were calculated from ionosonde measurements, the observations from other sectors involved direct measurement from satellite and the Incoherent Scatter Radar (ISR) observations. The importance of the PRE in ionospheric electrodynamics was highlighted, the better in the use of either the virtual or real heights of the F-layer in inferring vertical drift velocities were enumerated, revealing the strengths and weakness of each method. The general observations revealed that PRE peak magnitude is commonly weaker in the African region in comparison with the American/Peruvian and Indian sectors, seasonal and solar activity dependent, and could be higher during either magnetic quiet or disturbed activity than when both magnetic activity conditions are combined. The first work to present a regional PRE model around the African equatorial ionization anomaly region (Adebesin et al model) was mentioned. The relevance of the E × B drift in quantifying the daytime equatorial electrojet (EEJ) current was also discussed.
A O Idowu, I A Adimula, and G I Ojerheghan
IOP Publishing
This study considered the horizontal component of the magnetic field, H, which is a characteristic of Equatorial Electrojet (EEJ). Using Magnetic Data Acquisition System (MAGDAS) data preserved for the year 2009, variations in H strength were determined in 10 stations in Africa and Asia sector. The seasonal and annual fluctuations in the H-component of the Earth’s magnetic field were studied using hourly data of the horizontal magnetic field component. For the hourly fluctuation, the baseline values of H were estimated using the average values around local midnight hours between 2300 and 0200 local-time (LT) and subtracted from other hourly values; for seasonal and yearly analysis, the monthly and annual averages were computed. In all seasons, seasonal variations were higher in equatorial stations than in anti-equatorial stations, while maximum values of SqH were recorded in the equinoctial season, with an annual highest peak value of 70.96 nT in Langkawi (LKW; 6.30°S, 99.78°E) and the lowest peak value of 27.45 nT in Cooktown (CKT; 15.48°N, 145.25°E) both at 1300 LT.
I. Adimula, J. Ojo, Samuel Toluwalope Ogunjo, M. Ajewole, S. Falodun, A. A., Willoughby and M. Usikalu
IOP Publishing
I.A Adimula1, J. S. Ojo2, S. T. Ogunjo2, M.O Ajewole2, S.E Falodun2, A. A Willoughby3, and M. R Usikalu4 1 Department of Physics, University of Ilorin, Ilorin, Kwara State, Nigeria 2 Department of Physics, Federal University of Technology Akure, Ondo State 3 Department of Physics, Redeemer’s University Ede, Osun State 4 Department of Physics, Covenant University, Ota, Ogun State, Nigeria Email: ojojs_74@futa.edu.ng, josnno@yahoo.com, adimula@unilorin.edu.ng List of Organizing Committee, Scientific Committee, Editorial Committee, Invited Speakers, Sponsors, are available in this pdf.
Shola Adebiyi, Isaac Adimula, and Olushola Oladipo
Nigerian Society of Physical Sciences
This paper compares the quiet time variation of the Total Electron Content (TEC) over four stations located at high and mid latitudes in the northern and southern hemispheres of the African-European longitudes. Five years Global Positioning System (GPS) data, from 2002 to 2006, representing the periods of high to low solar activities were used for the study. Generally, the maximum diurnal values of TEC are observed between 10:00 – 14:00 LT in all the stations during the periods investigated. The minimum values of TEC are observed during the pre-sunrise hours for the two mid latitude stations and around the pre-midnight/post-midnight for the high latitude stations. The maximum values of TEC, however vary with season, latitude and solar activity in all the stations. The values decrease with increase in latitudes and decrease in solar activity. The values range between 10 – 32 and 11 – 50 TECU respectively, for high and mid latitudes for all the years considered. Seasonally, the highest values of TEC are generally observed during the equinoxes in all the stations except at the southern mid latitude station where it can as well be observed in summer, particularly during the Moderate Solar Activity (MSA) and Low Solar Activity (LSA) periods. The lowest values of TEC are observed in winter in all the stations in the southern hemisphere and can be observed in both winter and summer for stations in the northern hemisphere depending on the latitude and solar activity period. TEC variation also exhibits (1) asymmetry in the equinoctial values in all the stations and the magnitude is most pronounced during the period of High Solar Activity (HSA); (2) winter ionosphere anomaly feature, observed only in the northern hemisphere stations; and (3) daytime minimum and nighttime maximum in the diurnal structures of TEC at high latitude in the northern hemisphere during the winter. The nighttime maximum value was observed around 21:00 LT with magnitude that decreases with decrease in solar activity. The annual maximum value of TEC decreases with solar activity at all the stations, with the highest/lowest peak observed in HSA/LSA periods.
S. J. Adebiyi, J. O. Adeniyi, B. O. Adebesin, S. O. Ikubanni, I. A. Adimula, O. A. Oladipo, A. O. Olawepo, B. J. Adekoya, and B. W. Joshua
American Geophysical Union (AGU)
Information about the altitudinal distribution of ionospheric electron density (Ne) in the African equatorial region is very scanty. Such information is vital in modeling of key ionospheric parameters and in solving problems associated with ionospheric effect on the applications that depend on space‐based positioning and navigation systems. For the first time in the region, the entire Ne profile estimated by IRI is evaluated with profile deduced from Digisonde measurements at Ilorin (geog. 8.50°N, 4.50°E; dip. −7.9°) during low solar activity condition. Results obtained indicate marked discrepancies between the two profiles with magnitudes revealing local time and altitudinal and seasonal trends. The largest discrepancies are found between the post‐sunset and sunrise hours regardless of the seasons. IRI underestimates the Ne around the F1 region and is most obvious in September equinox and December solstice with deviation up to −42%. Further, IRI overestimates the Ne around the F2 peak at daytime, mostly in solstices with maximum deviation of 26% at F2 peak. All the three IRI topside models generally underestimate Ne between ~F2 peak height and ~800 km in all seasons except in June solstice. Beyond 800 km, the Digisonde, IRI‐NeQuick, and IRI‐2001 Corr profiles tend to converge, whereas the IRI‐2001 profiles still show marked divergence from the Digisonde profile in all seasons. Overall, the IRI‐NeQuick gives the best topside representation at this station at daytime/nighttime. The comparative analysis of Digisonde‐TEC and GPS‐TEC suggests that the Digisonde alone may not give a reliable estimate of the nighttime topside altitudinal distribution of Ne at this location.
O A Oladipo, J O Adeniyi, I A Adimula, A O Olawepo, A Olowookere, F U Salifu, S M Radicella, and B W Reinisch
Springer Science and Business Media LLC
S.J. Adebiyi, S.O. Ikubanni, B.O. Adebesin, J.O. Adeniyi, B.W. Joshua, I.A. Adimula, O.A. Oladipo, A.O. Olawepo, and B.J. Adekoya
Elsevier BV
B. O. Adebesin, J. O. Adeniyi, I. A. Adimula, S. J. Adebiyi, S. O. Ikubanni, O. A. Oladipo, and A. O. Olawepo
American Geophysical Union (AGU)
The study of ionization gradient (dN/dh) profile in the description of ionospheric dynamics is not common. This is the first attempt at finding the dependence of ionization gradient, solar quiet component (Sq (BH)), and bottomside thickness parameter (B0) in the African equatorial sector. Digisonde and Magnetic Data Acquisition System data collocated at an equatorial location were employed. Result was presented for sunrise (00 LT), midday (12 LT), sunset (18 LT), and midnight (00 LT) hours. The ionization gradient peak height remains unchanged at midday across all months. A percentage correlation of 93% existed in the inverse and direct linear relationship of dN/dh‐B0 at sunrise, and of Sq (BH)‐B0 at midday, respectively. Significant relationship between dN/dh and Sq (BH) was at sunset; for other hours, the relationship is poor. The multiple linear relationship of dN/dh‐Sq (BH)‐B0 parameters revealed that the dependence of dN/dh on Sq (BH) and B0 is highest at midday, and a model equation was presented. The dependence of dN/dh on the solar activity index (F10.7) holds at all the selected hours, and distinct only at midday and midnight for the Sq (BH)‐F10.7 and B0‐F10.7 patterns. Both the peak ionization gradient and the height it occurs maximizes/minimizes at 18 LT/06 LT. The importance of the F region dynamo at heights above 150 km was reported.
S. J. Adebiyi, J. O. Adeniyi, B. W. Reinisch, B. O. Adebesin, S. O. Ikubanni, I. A. Adimula, O. A. Oladipo, A. O. Olawepo, B. W. Joshua, and B. J. Adekoya
American Geophysical Union (AGU)
One inherent parameter in the extrapolation of ionospheric topside profile is the scale height, which can be derived from an ionogram. For the first time in the African equatorial region, the variation of digisonde‐derived scale height (Hm) is investigated at Ilorin (Geog. 8.50°N; 4.50°E; dip. –7.9°) during quiet and disturbed conditions. Diurnal pattern of Hm revealed a consistent but insignificant hump before sunrise, followed by a marked increase, maximizing around local noon, and a decrease thereafter till nighttime. The daytime values, however, shows significant seasonal differences. A striking observation is the highest value in December solstice and lowest during June solstice. This is attributed to the influence of ion‐neutral drag and topside thermal structure on the shape of the topside ionosphere. Hm also exhibits high correlation with the bottomside thickness parameter (B0) and the total electron content; however, it is generally moderate with F2 layer critical frequency (foF2) and peak height (hmF2). These correlations do not show significant seasonal dependence. The large network of Global Positioning System (receivers may serve as a good data source for the reconstruction of the topside profile owing to the excellent relationship between Hm and total electron content. The linear model developed to describe the dependence of Hm on B0 generally gives a good representation of Hm with digisonde‐B0 as input. Large discrepancies were observed with the three options of the IRI 2016‐B0 used as input. The B0 models, if well established at the station, could be an alternative source to estimate Hm.
O.O. Odeyemi, J.O. Adeniyi, O.A. Oladipo, A.O. Olawepo, I.A. Adimula, and E.O. Oyeyemi
Elsevier BV
Olumide Olayinka Odeyemi, Jacob Adeniyi, Olushola Oladipo, Olayinka Olawepo, Isaac Adimula, and Elijah Oyeyemi
Copernicus GmbH
Abstract. We investigated total electron content (TEC) at Ilorin (8.50∘ N 4.65∘ E, dip lat. 2.95) for the year 2010, a year of low solar activity in 2010 with Rz=15.8. The investigation involved the use of TEC derived from GPS, estimated TEC from digisonde portable sounder data (DPS), and the International Reference Ionosphere (IRI) and NeQuick 2 (NeQ) models. During the sunrise period, we found that the rate of increase in DPS TEC, IRI TEC, and NeQ TEC was higher compared with GPS TEC. One reason for this can be attributed to an overestimation of plasmaspheric electron content (PEC) contribution in modeled TEC and DPS TEC. A correction factor around the sunrise, where our finding showed a significant percentage deviation between the modeled TEC and GPS TEC, will correct the differences. Our finding revealed that during the daytime when PEC contribution is known to be absent or insignificant, GPS TEC and DPS TEC in April, September, and December predict TEC very well. The lowest discrepancies were observed in May, June, and July (June solstice) between the observed values and all the model values at all hours. There is an overestimation in DPS TEC that could be due to extrapolation error while integrating from the peak electron density of F2 (NmF2) to around ∼1000 km in the Ne profile. The underestimation observed in NeQ TEC must have come from the inadequate representation of contribution from PEC on the topside of the NeQ model profile, whereas the exaggeration of PEC contribution in IRI TEC amounts to overestimation in GPS TEC. The excess bite-out observed in DPS TEC and modeled TEC indicates over-prediction of the fountain effect in these models. Therefore, the daytime bite-out observed in these models requires a modifier that could moderate the perceived fountain effect morphology in the models accordingly. The daytime DPS TEC performs better than the daytime IRI TEC and NeQ TEC in all the months. However, the dusk period requires attention due to the highest percentage deviation recorded, especially for the models, in March, November, and December. Seasonally, we found that all the TECs maximize and minimize during the March equinox and June solstice, respectively. Therefore, GPS TEC and modeled TEC reveal the semiannual variations in TEC.
B. O. Adebesin, J. O. Adeniyi, O. A. Oladipo, A. O. Olawepo, and I. A. Adimula
American Geophysical Union (AGU)
The electron ionization gradient (dN/dh) characteristics were quantitatively presented using data from Ilorin (8.50°N, 4.68°E) Digisonde during low solar activity. Ionogram inversion using calculated average representative profile program was employed in obtaining the profile data. Results were presented for both the minimum and maximum gradient positions above the 150‐km altitude. The daily hours were classified into four segments. Our result revealed that at sunset/postsunset and nighttime hours, the ionization magnitude at the point of maximum gradient during the equinoxes is twice the value in solstices. This feature of the higher ratio in the equinox is less distinct at sunrise/presunrise and noon/postnoon hours and not pronounced at all hours of the minimum gradient position. The time of occurrence of the maximum gradient for the sunrise/prenoon, noon/postnoon, and nighttime hours, respectively, are 07 LT, 17 LT, and 23 LT for all seasons. For this same diurnal segments at the point of minimum gradient, it is 05 LT, 12 LT, and 04 LT, respectively. The height (hdN) at which the highest gradient was reached is ≈310 km, occurring during the sunset/postsunset hours for both the maximum and minimum gradient positions. The lowest (≈235 km) was reached during the sunrise/prenoon hours. hdN at the position of maximum ionization is lower than the real height (hmF2) across all seasons. The percentage difference in dN/dh magnitude at the position of maximum and minimum gradients is lowest at noon/postnoon period and highest at sunrise/prenoon hours. The various physical processes involved were discussed. We established an inverse relationship between the pattern of dN/dh and vertical drift velocity.
B.W. Joshua, J.O. Adeniyi, O.A. Oladipo, P.H. Doherty, I.A. Adimula, A.O. Olawepo, and S.J. Adebiyi
Elsevier BV
O. A. Oladipo, J. O. Adeniyi, P. H. Doherty, S. M. Radicella, I. A. Adimula, and A. O. Olawepo
American Geophysical Union (AGU)
Scintillation of radio waves in the L‐band frequency is a regular occurrence at the equatorial and auroral regions at night most especially during high solar activity periods. Scintillation is caused by plasma density irregularities, and this could cause loss of lock of Global Navigation Satellite System (GNSS) signals leading to impairment of the applications that rely on this system. A study on the occurrence of scintillation activity over Ilorin (latitude = 8.48°N, longitude = 4.67°W, and geomagnetic latitude = 1.89°S), Nigeria was done using S4 index data from NovAtel GPStation‐2 receiver (2009–2012) and NovAtel GPStation‐6 receiver (August 2013 to December 2016) which are both located at this station. The solar maximum period of the solar cycle 24 is located well within the period of this investigation; hence, this study provides opportunity to see the occurrence pattern of scintillation during different seasons as well as the pattern from low solar activity to solar maximum. The results obtained showed that scintillation occurs between 21:00 LT and 04:00 LT at the peak of the occurrence in 2014. The time window of occurrence decreases with decrease in solar activity. Similarly, scintillation activity was observed to be more regular during high solar activity and it has two peaks of occurrence in March and October. A solar activity trend was observed in scintillation occurrence; scintillation activity increases with increase in the level of solar activity.
I. A. Adimula, O. A. Oladipo, and S. J. Adebiyi
Springer Science and Business Media LLC
S. J. Adebiyi, I. A. Adimula, O. A. Oladipo, and B. W. Joshua
American Geophysical Union (AGU)
A reliable ionospheric specification by empirical models is important to mitigate the effects of the ionosphere on the operations of satellite‐based positioning and navigation systems. This study evaluates the capability of the International Reference Ionosphere (IRI) and IRI extended to the plasmasphere (IRI‐Plas) models in predicting the total electron content (TEC) over stations located in the southern hemisphere of the African equatorial and low‐latitude region. TEC derived from Global Positioning System (GPS) measurements were compared with TEC predicted by both the IRI‐Plas 2015 model and the three topside options of the IRI 2012 model (i.e., NeQuick (NeQ), IRI 2001 corrected factor (IRI‐01 Corr), and the IRI 2001(IRI‐01)). Generally, the diurnal and the seasonal structures of modeled TEC follow quite well with the observed TEC in all the stations, although with some upward and downward offsets observed during the daytime and nighttime. The prediction errors of both models exhibit latitudinal variation and these showed seasonal trends. The values generally decrease with increase in latitude. The TEC data‐model divergence of both models is most significant at stations in the equatorial region during the daytime and nighttime. Conversely, both models demonstrate most pronounced convergence during the nighttime at stations outside the equatorial region. The IRI‐Plas model, in general, performed better in months and seasons when the three options of the IRI model underestimate TEC. Factors such as the height limitation of the IRI model, the inaccurate predictions of the bottomside and topside electron density profiles were used to explain the data‐model discrepancies.
S.J. Adebiyi, I.A. Adimula, and O.A. Oladipo
Elsevier BV
S.J. Adebiyi, I.A. Adimula, and O.A. Oladipo
Elsevier BV
B.O. Adebesin, J.O. Adeniyi, I.A. Adimula, O.A. Oladipo, A.O. Olawepo, and B.W. Reinisch
Elsevier BV
B.W. Joshua, J.O. Adeniyi, B.W. Reinisch, I.A. Adimula, A.O. Olawepo, O.A. Oladipo, and S.J. Adebiyi
Elsevier BV