Department Of Physics

Permanent URI for this community

https://ir.unilag.edu.ng/handle/123456789/3391
The Department provides tutorial and/or research courses at undergraduate and postgraduate levels leading to the award of the degrees of Bachelor of Sciences (Honours) (B.Sc.), the Master of Science (M.Sc.), Master of Philosophy (M.Phil.) and Doctor of Philosophy (Ph.D.) in Physics respectively. Physics is one of the basic experimental physical sciences.

Browse

Browsing Department Of Physics by Issue Date

Filter results by year or month
Now showing 1 - 20 of 59
  • Item
    Open Access
    Environmental protection and management: A need for oil spill survey
    (2000) Nwakuche, E. E
    The problem of oil pollution in various land, Marine and estuarine environments has received considerable scientific attention with respect to the fates and effects of petroleum spills, as well as inherent toxicities to the specific biological and physical ecosystem components and individual species. It is most certain that the incidence of oil spills resulting from tanker traffic, offshore and onshore drilling and associated activities will increase in the years to come as the world's demand for petroleum and petroleum products continues to be on the rise. Drift is a large scale phenomena and is a measure of the movement of the centre of mass of an oil slick. Drift is primarily controlled by wind, waves and surface currents and is independent of the spreading and spill volume. Drift is also strongly influenced by tidal currents. This paper seeks to detail how to improve the management of basic resources (e.g., oil) and the rehabilitation of environmental conditions through the involvement of surveyors. Numerous government agencies have specific functions anti activities related to environmental protection and management. Assembling the environmental components from these agencies requires detailed survey of the environment. The surveyor's details in terms of plans, maps, photographs and database provide a strong centralized control. The surveyor have four major functions in the control of oil pollution: evaluation which involves prospective investigation of the polluted area; research which involves adopting standards through mathematical model, monitoring which involves the impact assessment and information exchange with other professionals.
  • Item
    Open Access
    Electromagnetic Modeling With Wave Tilt And Reflection Coefficient: An Application to Stratified Earth Media Using Radio And Low Frequencies
    (Journal of Geophysics & Engineering: Institute of Physics (IOP), U.K., 2006) Olowofela, J.A.; Ozebo, V.C.
    Many models using electromagnetic sounding techniques have been formulated for use in exploration activities. In deriving the governing equations for the models, Maxwell’s equations are used and the earth is taken as a layered medium. Using these boundary conditions, the Sommerfeld integrals are obtained for several models. However, the difficulties and limitations posed by the iterations of the functions, especially the strong oscillations and slow convergence of the Bessel function, call for a search for new methods. This work aims to formulate models, with the advantage of bypassing the problems highlighted above, and to discover new response parameters not considered by the older models due to the limitations of time. Three measurable field parameters, (1) amplitude of the correction factor to the wave tilt, (2) phase of the amplitude of the correction factor to the wave tilt and (3) reflection coefficient, were calculated from this model with various conductivity contrasts over a two-layered earth. Two cases of a top layer overlying a more conductive basement and a more conductive top layer overlying a resistive basement were considered with a radio frequency of 125 kHz and a low frequency of 10 Hz. The model was tested using data from existing models and was then applied to a homogeneous and a layered earth. Results revealed that the phase of the amplitude of the correction to the wave tilt was found to be most diagnostic of the changes in layer parameters. Also, depths of 20 m and 2000 m were achieved with the two respective frequency values. The reflection coefficient was discovered to be an important parameter for detecting layered earth structures, in addition to other parameters. Furthermore, an inverse relationship between the transverse electric and transverse magnetic modes of the reflection coefficient is established.
  • Item
    Open Access
    Radiation Exposure to Workers and Villagers in and Around Some Quarry Sites in Ogun State of Nigeria
    (Medwell Publications, 2008) Odunaike, R.K; Ozebo, V.C.; Alausa, S.K; Alausa, I.M
    In this research, the authors employed radiation detection methods to examine the radiation intensity or exposure at 5 quarry sites and their respective neighborhood villages in Ogun State of Nigeria. The highest annual dose rate or exposure of 49.1 micro Sv year 1 was recorded at Equation Limited (Q3) in Obafemi Owode Local Government area in Ogun State of Nigeria. However, this result (49.1 micro Sv year 1) and others from the remaining locations or sites are smaller than the world average of 70 micro Sv year 1 but recommended that workers at quarry sites should always put on masks to eliminate or reduce the amount of radioactive inhalation. Regular comprehensive monitoring of radiation level of each worker by putting on Thermo Luminescent Dosimeters (TLDs) which could be read and interpreted must be encouraged.
  • Item
    Open Access
    Identification of depth to top of limestone body within a concession at Ibese, Southwestern Nigeria, using vertical electric sounding
    (Medwell Publications, 2008) Ozebo, V.C.; Odunaike, R.K; Balogun, A.A
    he depth to top of limestone body within a concession at Ibese, in Ogun state, Southwestern Nigeria was evaluated using the Vertical Electric Sounding (VES). The electrical resistivity method employing the VES technique was used to carry out the geophysical investigation and a total 10 VES data was acquired. Three curve types were identified from the acquired data which are the H, A and HK-type curves. Also a geo-electric section was obtained from the result of the field sounding areas, where all the materials above the limestone is regarded as an overburden. The study area (line) spans 5 km of which the trend (direction) of the limestone was found to be NW-SE. VES locations 2, 5, 6, 7, 8 were found to have a shallow depth which is less than 6 m and can be said to be of economic importance.
  • Item
    Open Access
    Comparisons of observed ionospheric F2 peak parameters with IRI-2001 predictions over South Africa
    (Elsevier Ltd, 2009) Adewale, Adekola; Oyeyemi, Elijah; McKinnell, Lee-Anne
    The monthly means of the ionospheric F2 peak parameters (foF2 and hmF2) over three stations in South Africa (Grahamstown,33.31S, 26.51E, Madimbo, 22.41S, 26.51E, and Louisvale, 28.51S, 21.21E) were analyzed and compared with IRI-2001, using CCIR (Comite´ Consultatif International des Radio communications)and URSI (Union Radio-Scientifique Internationale coefficients)options. The analysis covers a few selected quiet and disturbed days during various seasons represented by the months of January, April, July and October 2003. IRI-2001 generally over estimates hmF2 for both quiet and disturbed days and it over estimates and underestimates foF2 at different times for all the stations. In general, foF2 is predicted more accurately by IRI-2001 than hmF2, and on average, the CCIR option performed better than the URSI option when predicting both foF2 and hmF2. In general, the model generates good results, although some improvements are still necessary to be implemented in order to obtain better predictions. There are no significant differences in the model predictions of hmF2 and foF2 for quiet and disturbed days.
  • Item
    Open Access
    Infrared Emission Properties of Ho doped KPb2Cl5
    (Materials Research Society, 2009-02-24) Hömmerich, U; Oyebola, O; Brown, E; Trivedi, S.B; Bluiett, A.G; Zavada, J.M
    We report on the optical properties of Ho doped KPb2Cl5 (Ho: KPC) for potential applications as an infrared (IR) solid-state gain medium. The investigated crystal was synthesized from commercial starting materials of PbCl2, KCl, and HoCl3 followed by several purification steps including directional freezing, zone-refinement, and chlorination. The Ho: KPC crystal was subsequently grown by Bridgman technique. Following optical excitation at 885 nm, several IR emission bands were observed at room-temperature with average wavelengths at 1.07, 1.18, 1.35, 1.65, 2.00, 2.89, and 3.96 mm. The emission at 3.96 mm originated from the 5I5 ® 5I6 transitions of Ho3+ and was further evaluated for possible applications in mid-IR lasers. The decay time of the 5I5 excited state was measured to be 5.0 ms at room-temperature. The long 5I5 lifetime is favorable for laser applications and indicates that non-radiative multi-phonon relaxations are small in Ho: KPC. Based on a Judd-Ofelt analysis, the emission quantum efficiency was determined to be near unity resulting in a peak emission cross-section of 0.62x10-20 cm2 at 3.96 mm. A drawback for laser applications is the long decay time of the lower 5I6 state with a value of 4.8 ms . Since the 3.96 mm transition terminates in the 5I6 level, its long lifetime will lead to population bottlenecking, which limits possible mid-IR lasing to pulsed and quasi-cw operation.
  • Item
    Open Access
    Stimulation of Haemopoetic Activity in Bone Marrow and Deformation of Red Blood Cells in Albino Mice, Mus musculus Exposed to Radiations from GSM Base Stations.
    (Sierra Leone Journal of Biomedical Research, 2010) Otitoloju, A.A.; Osunkalu, V.O.; Akogun, M.M.; Obe, I.A.; Adewale, A.O.; Akinde, O.R.
    The levels of radiofrequency radiations around two global systems for mobile communication (GSM) base stations located around a residential quarter and workplace complex were measured. The effects of the radiofrequency radiations on albino mice placed in exposure cages and located around the base stations over a six months period were investigated. The levels of radiofrequency (RF) radiations around the base stations were found to range between 383 mV/m to 730 mV/m compared to 59 mV/m in control stations. In the exposed mice, a pattern of pancytosis was observed and significant increases were observed in the Packed Cell Volume (PCV), White Cell Count (WBC), Platelet count (PLT) and Red Cell Count (RCC) throughout the period of exposure in both stations when compared with control values. No significant (p>0.05) differences were observed in these values when both stations were compared. After 90 days of exposure, marginal increases occurred in the mean cell volume of exposed mice at station 1 and 2 (53.1±3.6fl Vs 55.9±1.8fl and 57.9±0.25fl respectively), with the mean cell haemoglobin concentration showing significant reduction after 180 days of exposure at station 2 (27.9±2.4g/dl Vs 25.7±0.29g/dl; p<0.05). Marked anisopoikilocytosis and striking polychromasia were seen on peripheral films of exposed mice, with bone marrow showing increased cellularity. Exposure of the mice to radiofrequency radiations therefore resulted in cellular proliferation with subsequent stimulation of haemopoetic activity and probable increase in the utilisation of folate and iron resulting in increased mean cell volume (MCV) and reduction in mean cell haemoglobin concentration (MCHC). The fears of a possible biological effect of chronic human exposure to radiofrequency radiations may therefore be reasonable enough to justify the clamour for the reduction in the proliferation of GSM base stations across the country.
  • Item
    Open Access
    Preliminary Study on the Induction of Sperm Head Abnormalities in Mice, Mus musculus, Exposed to Radiofrequency Radiations from Global System for Mobile Communication Base Stations.
    (Bull Environ Contam Toxicol, 2010) Otitoloju, A.A.; Obe, I.A.; Adewale, A.O.; Otubanjo, O.A.; Osunkalu, V.O.
    The exposure of male mice to radiofrequency radiations from mobile phone (GSM) base stations at a workplace complex and residential quarters caused 39.78 and 46.03%, respectively, in sperm head abnormalities compared to 2.13% in control group. Statistical analysis of sperm head abnormality score showed that there was a significant (p\0.05) difference in occurrence of sperm head abnormalities in test animals. The major abnormalities observed were knobbed hook, pin-head and bananashaped sperm head. The occurrence of the sperm head abnormalities was also found to be dose dependent. The implications of the observed increase occurrence of sperm head abnormalities on the reproductive health of humans living in close proximity to GSM base stations were discussed.
  • Item
    Open Access
    Comparison between observed ionospheric foF2 and IRI-2001 predictions over periods of severe geomagnetic activities at Grahamstown, South Africa
    (Elsevier Ltd, 2010) Adewale, Adekola; Oyeyemi, Elijah; Ofuase, U.
    The observed ionospheric F2 critical frequency (foF2) values over a South Africa mid-latitude station, Grahamstown, (geographic coordinates: 33.3 S, 26.5 E), were analysed and compared with International Reference Ionosphere (IRI) model, using the CCIR (Comite ´ Consultatif International des Radio communications) and URSI (Union Radio-Scientifique Internationale) coefficients, during four geomagnetically disturbed days in the year 2000. These days are April 5, May 23, August 10 and September 15. The data were analysed for five days around the storm day. Comparisons between the IRI-2001 predicted foF2 values, using both CCIR and URSI coefficients and the observed values are shown with their root-mean-square error (RMSE) and the relative deviation module mean (rdmm) for the various storm periods. The CCIR option performed more accurately than the URSI option. In general, the model generates good results when compared with observed foF2 values during geomagnetic storms, although some improvements are still necessary to be implemented in order to obtain better predictions.
  • Item
    Open Access
    Level of Radiofrequency (RF) Radiations from GSM Base Stations and its Biological Effects on Albino Mice, Mus musculus
    (Journal of Applied Sciences and Environmental Management, 2010) Otitoloju, A.A.; Osunkalu, V.O.; Obe, I.A.; Adewale, A.O.; Akinde, O.R.
    Levels of radiofrequency radiations around two global systems for mobile communication (GSM) base stations located in the vicinity of a residential quarter and workplace complex were measured. The effects of the radiofrequency radiations on albino mice placed in exposure cages and located around the base stations over a six months period were carried out. The levels of radiofrequency (RF) radiations around the base stations were found to be between 488.51mV/m to 625.49mV/m compared to 59 mV/m in control stations. The results of the weight change experiment showed that over the 180 days of observation, there was weight gain in the exposed and control mice groups. Statistical comparisons of mean weight changes between exposed mice and control mice showed that there were no significant (P>0.05) differences between the weight of the test animals. The hematological studies revealed an elevation of white blood cell (WBC) counts in mice exposed to RF radiations compared to control group. There was however no significant (P>0.05) difference between the red blood cell counts in the exposed and control mice. There was also no significant (P>0.05) difference in the hemoglobin and glucose levels in the blood of both exposed and control mice groups. The red blood cells in exposed mice were however found to contain a higher number of macrocytes, poikilocytes, polychromatic cells and fewer target cells than the control mice. Histological studies of the heart and kidney of exposed mice showed only slight tissues deformities in kidneys of exposed mice compared to control. The relevance of these findings in setting radiofrequency radiation exposure guidelines and the need for more studies with widely varying biological parameters is very necessary as Nigeria leaps further into the communication age.
  • Item
    Open Access
    Comparison between observed ionospheric foF2 and IRI-2001 predictions over periods of severe geomagnetic activities at Grahamstown, South Africa
    (Advances in Space Research, 2010) Adewale, Adekola; Oyeyemi, Elijah; Ofuase, Uche
    The observed ionospheric F2 critical frequency (foF2) values over a South Africa mid-latitude station, Grahamstown, (geographic coordinates: 33.3 S, 26.5 E), were analysed and compared with International Reference Ionosphere (IRI) model, using the CCIR (Comite´Consultatif International des Radio communications) and URSI (Union Radio-Scientifique Internationale) coefficients, during four geomagnetically disturbed days in the year 2000. These days are April 5, May 23, August 10 and September 15. The data were analysed for five days around the storm day. Comparisons between the IRI-2001 predicted foF2 values, using both CCIR and URSI coefficients and the observed values are shown with their root-mean-square error (RMSE) and the relative deviation module mean (rdmm) for the various storm periods. The CCIR option performed more accurately than the URSI option. In general, the model generates good results when compared with observed foF2 values during geomagnetic storms, although some improvements are still necessary to be implemented in order to obtain better predictions.
  • Item
    Open Access
    Variability of foF2 in the African equatorial ionosphere
    (Elsevier Ltd, 2010) Adewale, A.O.; Akala, A.O.; Oyeyemi, E.O.; Somoye, E.O.; Adeloye, A.B.
    This paper presents the impact of diurnal, seasonal and solar activity effects on the variability of ionospheric foF2 in the African equatorial latitude. Three African ionospheric stations; Dakar (14.8°N, 17.4°W, dip: 11.4°N), Ouagadougou (12.4°N, 1.5°W, dip: 2.8°N) and Djibouti (11.5°N, 42.8°E, dip: 7.2°N) were considered for the investigation. The overall aim is to provide African inputs that will be of assistance at improving existing forecasting models. The diurnal analysis revealed that the ionospheric critical frequency (foF2) is more susceptible to variability during the night-time than the day-time, with two peaks in the range; 18–38% during post-sunset hours and 35– 55% during post-midnight hours. The seasonal and solar activity analyses showed a post-sunset September Equinox maximum and June Solstice maximum of foF2 variability in all the stations for all seasons. At all the stations, foF2 variability was high for low solar activity year. Overall, we concluded that equatorial foF2 variability increases with decreasing solar activity during night-time.
  • Item
    Open Access
    Evaluation of rainfall trends in Nigeria for 30 years (1978-2007)
    (2010-11-04) Obot, N. I.; Chendo, M. A. C.; Udo, S.O.; Ewona, I. O.
    The issue of climate change appears to be on the fore burner and it cannot be ascertained to occur without evidence. Rainfall is one of the climatic factors that can indicate climate change. In this work, the non-parametric Mann-Kendall test is used to test for significant trend in rainfall in Nigeria through randomly selected locations in the six geopolitical zones within a 30 years period (1978-2007). The selected locations are; Maiduguri (13°10',11°50') in the North East, Kaduna (7°27',10°31') in the North West, Lokoja (6°45',7°43') in the North Central, Ibadan (3°53',7°22') in the South West, Enugu (7°30',6°27') in the South East and Calabar (8°28',4°57') in the South South. During the 30 years period, the yearly average rainfalls (mm) were 580.5, 1187.5, 1228.7, 1317.2, 1753.8 and 2925.6, respectively. While the rest of the locations had no significant trend yet Maiduguri showed an increasing trend at a rate of 9.88 mm/year, where formally the trend there from the period 1961-1990 was decreasing. This change could either be a problem or blessing to dwellers in that location and there is need for continuous monitoring.
  • Item
    Open Access
    Responses of equatorial F region to different geomagnetic storms observed by GPS in the African sector
    (JOURNAL OF GEOPHYSICAL RESEARCH, 2011) Adewale, A.O.; Oyeyemi, E.O.; Adeloye, A.B.; Ngwira, C.M.; Athieno, R.
    This article presents the first results regarding the investigation of the response of the equatorial ionospheric F region in the African sector during geomagnetic storm periods between April 2000 and November 2007 using GPS‐derived vertical total electron content observed at Libreville, Gabon (0.35°N, 9.67°E, dip latitude −8.05°S). We performed a superposed epoch analysis of the storms by defining the start time of the epoch as the storm onset time. During geomagnetic storms, the altered electric fields contribute significantly to the occurrence of negative and positive ionospheric storm effects. Our results showed that the positive storm effects are more prevalent than the negative storm effects and generally last longer irrespective of storm onset times. Also, the positive storm effects are most pronounced in the daytime than in the premidnight and postmidnight periods.
  • Item
    Open Access
    Groundwater Assessment in Apapa Coast-Line Area of Lagos using Electrical Resistivity method
    (Scholarlink Research Institute, UK, 2011) Ozebo, V.C.; Ajiroba, S.O
    A study was conducted on some physical characteristics of geological formations in Apapa, a coast-line area of Lagos state with the purpose of determining the extent of deterioration in the quality and quantity of the groundwater due to saline water intrusion and other factors. Applying the Schlumberger configuration of Vertical electrical sounding, (VES) on five locations, data were collected and analysed using both the partial curve matching and microprocessor iterative techniques. Geoelectric sections along XX – XX’, comprising of VES point 3 and 1, and along YY – YY’ made up of VES points 1 and 4 were generated along south-north and West-East directions respectively. The analysed data revealed the presence of sand, clay, sandy clay, clayey sand formations and some intrusions of saline water in the area. The results also indicated that the safest depth for groundwater (devoid of saline intrusion) is 34 m and beyond.
  • Item
    Open Access
    Low solar activity variability and IRI 2007 predictability of equatorial Africa GPS TEC
    (Elsevier Ltd, 2011) Adewale, A.O.; E.O. Oyeyemi, E.O.; Cilliers, P.J.; McKinnell, L.A.; Adeloye, A.B.
    Diurnal, seasonal and latitudinal variations of Vertical Total Electron Content (VTEC) over the equatorial region of the African continent and a comparison with IRI-2007 derived TEC (IRI-TEC), using all three options (namely; NeQuick, IRI01-corr and IRI-2001), are presented in this paper. The variability and comparison are presented for 2009, a year of low solar activity, using data from thirteen Global Positioning System (GPS) receivers. VTEC values were grouped into four seasons namely March Equinox (February, March, April), June Solstice (May, June, July), September Equinox (August, September, October), and December Solstice (November, December, January). VTEC generally increases from 06h00 LT and reaches its maximum value at approximately 15h00–17h00 LT during all seasons and at all locations. The NeQuick and IRI01-corr options of the IRI model predict reasonably well the observed diurnal and seasonal variation patterns of VTEC values. However, the IRI-2001 option gave a relatively poor prediction when compared with the other options. The post-midnight and post-sunset deviations between modeled and observed VTEC could arise because NmF2 or the shape of the electron density profile, or both, are not well predicted by the model; hence some improvements are still required in order to obtain improved predictions of TEC over the equatorial region of the Africa sector.
  • Item
    Open Access
    Determined Optimization Technique for Solving Over-Determined Linear Systems
    (2011-09-28) Akala, A. O; Adepoju, J.A; Adeloye, A.B; Somoye, E.O; Oyebola, O.O; Oyeyemi, E.O; Olopade, M.O; Adewale, A.O; Yinka-Banjo, C; Ojiako, C
    This paper presents an optimization technique for solving linear system problems with more number of equations than unknown variables using Euclidean Space theory and least squares method. In view to automating the technique, we developed software in FORTRAN code for a generalized case. The technique was applied to determine the position of a Global Positioning System (GPS) receiver on the earth surface for arbitrarily positioned twelve GPS satellites. The technique is numerically friendly, and can be conveniently used to simulate problems involving linear systems.
  • Item
    Open Access
    Concentration Dependent Studies on the Laser-Induced Mid-Infrared Emission from KCl-NaCl Tablets
    (Photonics Society of Poland, 2011-12-31) Oyebola, O; Hommerich, U; Brown, E; Clayton, S.C yang; Trivedi, S.B; Samuels, A.C; Snyder, A.P
    Laser Induced Breakdown Spectroscopy (LIBS) is a technique for determining the elemental composition of a chemical substance [1].Pumping with ab064nm Nd:YAG pulse laser, mid- infrared emissions from LIBS plasma produced from KCl were examined between 2.0μm and 4.5μm, with atomic emission lines observed at 2.72μm, 3.15μm, 3.77μm and 4.05μm for potassium, consistent with NIST atomic spectra database. With further focus on the 2.72μm emission, detection limit studies were carried on different concentration samples of KCl_NaCl mix, to determine the detection limit of potassium (K). A limit of detection of ~0.19wt%/wt wasobtained for potassium in the mid-IR region
  • Item
    Open Access
    Low solar activity variability and IRI 2007 predictability of equatorial Africa GPS TEC
    (Advances in Space Research, 2012) Adewale, A. O.; Oyeyemi, E. O.; Cilliers, P. J.; McKinnell, L. A.; Adeloye, A. B
    Diurnal, seasonal and latitudinal variations of Vertical Total Electron Content (VTEC) over the equatorial region of the African continent and a comparison with IRI-2007 derived TEC (IRI-TEC), using all three options (namely; NeQuick, IRI01-corr and IRI-2001), are presented in this paper. The variability and comparison are presented for 2009, a year of low solar activity, using data from thirteen Global Positioning System (GPS) receivers. VTEC values were grouped into four seasons namely March Equinox (February, March, April), June Solstice (May, June, July), September Equinox (August, September, October), and December Solstice (November, December, January). VTEC generally increases from 06h00 LT and reaches its maximum value at approximately 15h00–17h00 LT during all seasons and at all locations. The NeQuick and IRI01-corr options of the IRI model predict reasonably well the observed diurnal and seasonal variation patterns of VTEC values. However, the IRI-2001 option gave a relatively poor prediction when compared with the other options. The post-midnight and post-sunset deviations between modeled and observed VTEC could arise because NmF2 or the shape of the electron density profile, or both, are not well predicted by the model; hence some improvements are still required in order to obtain improved predictions of TEC over the equatorial region of the Africa sector.
  • Item
    Open Access
    A study of L-band scintillations and total electron content at an equatorial station, Lagos, Nigeri
    (RADIO SCIENCE, 2012) Adewale, A.O.; Oyeyemi, E.O.; Adeloye, A.B.; Mitchell, C.N.; Rose, J.A.R.; Cilliers, P. J.
    In this paper we present the first results from measurements of scintillation and total electron content (TEC) from an equatorial station, Lagos (Latitude 6.5 N, Longitude 3.4 E, magnetic latitude 3.03 S), Nigeria, using a Novatel GSV4004B GPS ionospheric scintillation and TEC monitor. Details are presented for data collected between February 2010 and August 2010. The results show that the presence of some large scale depletions of TEC or plasma bubbles may be noted during the evening hours and that TEC depletions correspond to increased rate of change of TEC (ROT). This confirms that plasma bubbles are associated with large scale irregularities. It is also established that enhanced amplitude scintillation (S4) corresponds quite well with TEC depletions and increases in ROT. The diurnal and seasonal percentage occurrence for different levels of scintillation activity has peaks in the equinox months (March and April) at 23:00 LT