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SOLAR QUIET DAILY IONOSPHERIC VARIATIONS IN THE AFRICAN REGION

ABSTRACT

Solar quiet daily (Sq) ionospheric variations has been studied using four African stations, namely, Mbour (MBR), Addis Ababa (AAB), Hermanus (HRM) and Bangui (BANG). These stations are located in the West, East, South, and Central African regions respectively. The geomagnetic data for the year 1987 was used for this study since it is a year that all these stations had data in the geomagnetic components: – horizontal, H; declinational D; and vertical, Z. 

The diurnal, monthly, seasonal and day-to-day variations of the Sq variations in these geomagnetic elements were studied. The study shows that the variations of Sq in the geomagnetic elements were a dusk to dawn phenomenon, none zero variation was observed in the night. More variability were seen for the element D. The variation in the D element is seen to display the directional changes in the magnetic field as the earth’s rotation about the sun. An enhancement in Sq (H) variations in Addis Ababa station was observed. The observed enhancement in Sq (H) variations in Addis Ababa station is attributed to the enhanced dynamo action due to the influence of Equatorial Electro Jet (EEJ) current system. Equinoctial maximum in Sq(H) was observed for Mbour, Addis Ababa and Bangui stations and December Solstitial maximum observed for Hermanus station. A December solstitial maximum is observed in Sq(Z) for Hermanus, Mbour, and Bangui while a June solstitial maximum is observed for Addis Ababa. A June solstitial maximum is observed in Sq(D) for Hermanus and Bangui while a December solstitial maximum is observed for Mbour and Addis Ababa. The Day-day variability was observed in all the elements, these variability from one day to the next was seen to be both in amplitude and in phase, it does not have a definite pattern thus it is random. These day to day changes are attributed to changes in the ionospheric dynamo currents and ionospheric wind pattern.

 

 

CHAPTER ONE

INTRODUCTION

1.1 GEOMAGNETISM

Geomagnetism is a branch of the universal science of magnetism. It is the science that deals

with the study and characteristics of the magnetism of the earth. Geomagnetism deals with

the magnetic properties of the entire earth, which includes the magnetism of objects within

the earth.

Since the discovery of the earth’s magnetic properties ascribed to William Gilbert in 1600,

the origin of the earth’s magnetism has been thought to be one of the greatest unsolved

problems in physics. The earth’s magnetism has been proved by many scientists to have

both internal and external origins. The field of internal origin is called the main field while

the field of external origin has been considered to be very small compare to the field of

internal origin. This main field is thought to be produced by electric currents in the

liquid/fluid iron core. The composition of the fluid core has been estimated from seismic and

geochemical data which showed that the major constituent is liquid iron, with smaller

amounts of other less-dense elements. For the generation of the magnetic field the important

parameters of the core are its temperature, viscosity and electrical conductivity. Temperature

is known to be very poor inside the earth, but probably exceeds 30000C in the liquid core.

The electrical conductivity of iron at 200C is 107 ohm-1metre-1 and decreases with increasing

temperature. At the high temperatures and pressures in the core the electrical conductivity is

estimated to be around 3 - 5 X 105 ohm-1 metre-1, which corresponds to a good electrical

conductor (Lowrie, 2004). The field of external origin is thought to be due to the existence

of currents in the upper atmosphere due to the movement of conductive air across the lines

of force of the earth’s magnetic field, caused by solar heating.

The geomagnetic field is a dipole field having both North and South poles. The earth’s

magnetic poles are not located in the same place as the geographic North and South poles

which are defined by earth’s spin axis. The magnetic dipole axis is tilted by about 11

degrees with respect to the spin axis. At any point on the earth’s surface, the measured

magnetic field may differ appreciably in both magnitude and direction. In addition, the field ...Get Complete Material.


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