Approval Page
Table of Contents
List of Figures
List of Tables

CHAPTER 1: General Introduction
1.1       Introduction
1.2       Geomagnetic Temporal Variations
1.2.1    Transient Variations
1.2.2    Secular Variations
1.3       The Ionosphere
1.3.1    The D- Region
1.3.2    The E- Region
1.3.3    The F- Region
1.4       Ionospheric Dynamo Theory
1.4.1    Induced Current
1.4.2    External Current
1.5       Geomagnetic Field
1.5.1    Geomagnetic Elements
1.6       Solid Earth Structure
1.6.1    The Earth’s Crust
1.6.2    The Earth’s Mantle
1.6.3    The Earth’s Core
1.7       Ionospheric Current System
1.8       Purpose of the Study

CHAPTER : Literature Review
2.1       Introduction
2.2       Review on geomagnetic field variations and associated phenomena
2.3       Reviews on work on application of sq current in Earth mantle / study
            of Earth interior using sq current

CHAPTER 3: Theory, Source of Data and Method of Data Analysis
3.1       Theory of Sq current system application to the Earth interior
3.2       Sources of Data
3.3       Methods of Data Analysis

CHAPTER 4: Results and Discussion
4.1       Results Presentation
4.1.1    Sq Variation of HDZ Fields
4.1.2    Sq Amplitude Variation
4.1.3    Fourier Coefficients
4.1.4    H, D and Z Fourier Analyzed
4.1.5    Associated Legendre Polynomials (Schmidt Functions) for the Stations
4.1.6    Determination of Intermediate Coefficients
4.1.7    Spherical Harmonic Analysis (SHA) Coefficients
4.1.8    Determination of Equivalent Currents
4.1.9    Computation of Crust-Mantle Electrical Conductivity-Depth Values
4.2       Conductivity- Depth Profiles
4.3       Discussion of Results

CHAPTER 5: Conclusions and Recommendation
5.1       Conclusion
5.2       Recommendation

The solar quiet day ionospheric (Sq) current variations observed in Abuja (8.90oN, 7.39oE), Bangui (4.33oN, 18.57oE) and Addis Ababa (9.04oN, 38.77oE) have been used to delineate the mantle conductivity-depth structure along the geomagnetic equatorial African regions. Spherical harmonic analysis (SHA) was employed in separating the internal and external field contributions to the Sq variations. For each of the paired external and internal coefficients of the SHA, we used transfer function to compute the conductivity-depth profiles for the region. Regression lines fitted to the scatter data points enabled us to get average values from the many scattered points. Detailed error analysis based on the standard deviation of the conductivity values from the profile regression fittings revealed that the standard deviations of the conductivity values from the profiles are 0.011, 0.015 and 0.018 for Abuja, Addis Ababa and Bangui profiles respectively. Results of the study showed that conductivity-depth profiles of Abuja and Addis Ababa show similar trends. They slightly differ from Bangui especially from the crust to a depth of about 1000 km. The calculated average electrical conductivity values in Abuja and Addis Ababa were 0.007 Sm-1, 0.035 Sm-1 and 0.112 Sm-1 at 0.6 km, 30 km and 54 km respectively, all within the crust. The conductivity rose steadily to 0.141 Sm-1, 0.178 Sm-1and 0.224 Sm-1at 181 km, 241 km and 414 km depths respectively. These values were higher compared to Bangui values of 0.043 Sm-1, 0.096 Sm-1, 0.140 Sm-1, 0.198 Sm-1, and 0.221 Sm-1 at 56 km, 197 km, 316 km, 637 km and 831 km respectively. The rise was punctuated near 410 km depth corresponding to the transition zone. Within the lower mantle, results show that the Earth materials are in the same physical and chemical states. This assertion is depicted by the intersections of the profiles at some points at that depth. We equally observed increased electrical conductivity values in the Earth layers as well as deep depth of Sq current penetration. Two most Earth conductive layers were discovered in the magnetic equatorial zone. These layers lie between the depth of about 100 and 400 km within the upper mantle and beyond 1200 km in the lower mantle. Our result shows that the closer one goes towards the Earth’s magnetic equator; the more enhanced the Sq current and hence the deeper it can penetrate the Earth’s interior. Generally, the results are consistent with the global models (Arora et al., 1995; Campbell and Schiffmacher, 1988; Campbell et al., 1998; Obiekezie and Okeke, 2010 and Obiora et al., 2014).

1.1              Introduction
The Earth's magnetic field is generated in the fluid outer core by a self-exciting dynamo process. Electrical currents flowing in the slowly moving molten iron generate the magnetic field. In addition to sources in the Earth's core the magnetic field observable at the Earth's surface has sources in the crust and in the ionosphere and magnetosphere. The intensities of this geomagnetic field vary on a range of scales. It varies from one location on the Earth surface to another, from one solar cycle to another, from month to month, day to day and even from hour to the next.

Of the three components of this field namely the external, the anomalous induced and the main magnetic fields, the main magnetic field accounts for large regional variations in intensity and direction. This variation is easiest to observe during periods of low solar activity when large irregular disturbances are less frequent. For this reason it is often referred to as the solar quiet or Sq variation. Owing to the continuous time scale variation of the field, the amount of magnetization of rock materials is dependent on the changes of this field.

This field arising from magnetic materials in the Earth's crust varies on all spatial scales and is often referred to as the anomaly field. Knowledge of the crustal magnetic field is often very valuable as a geophysical exploration tool. This is because rocks and ores can become magnetized by induction in the geomagnetic field. Magnetic exploration involves mapping variations in the magnetic field to determine the location, size, depth and shape of deposits of such ores and consequently the local geology. The magnetic susceptibility of igneous rocks is generally much greater than sedimentary rocks. Consequently, the major magnetic anomalies observed in surveys of sedimentary basins usually result from the underlying basement rocks. Determining the depths of the tops of magnetic bodies is thus a way of estimating the thickness of the sediments.....

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