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THE STUDY OF LONGITUDINAL AND LATITUDINAL VARIATION OF EQUATORIAL ELECTROJET SIGNATURE AT STATIONS WITHIN THE 96°MM AND 210°MM AFRICAN AND ASIAN SECTORS RESPECTIVELY UNDER QUIET CONDITION

ABSTRACT

Solar quiet current (Sq) and Equatorial Electrojet (EEJ) are two current systems which are produced by electric current in the ionosphere. The enhancement of the horizontal magnetic field is the EEJ. This research is needed for monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. This study presents the longitudinal and latitudinal variation of equatorial electrojet signature at stations within the 96°   210°   African and Asian sectors respectively during quiet condition. Data fromeleven observatories were used for this study. The aim of this study is to investigate the equatorial variation of the solar quite ( ) current, as well as determine the longitudinal and latitudinal magnetic signatures on the EEJ at some African and Asian sectors under quiet condition. The objectives of the study therefore are to: Determine the longitudinal and latitudinal geomagnetic field variations during solar quiet conditions along the 96° 210°  ; Investigate monthly variation and diurnal transient seasonal variation; Measure the strength of the EEJ at stations within the same longitudinal sectors of 96° 210° ; and find out the factors responsible for the longitudinal and latitudinal variation of EEJ under solar quiet condition. Horizontal ( ) component of geomagnetic field for the year 2008 from Magnetic Data Acquisition System (MAGDAS) network were used for the study. The International Quiet Days (IQDs) were used to identify quiet days. Daily baseline values for each of the geomagnetic element  , can be obtained from 0 = 1⁄2 ( 24 + 1) where 0 is the dailybaseline. The daily baseline was subtracted from the hourly values to get the hourly departure from midnight for a particular day = − 0 where = 1 24 gives the measure of the hourly amplitude of the variation of . The monthly average of the diurnal variation was found. The seasonal variation of was found by averaging the monthly means for Lloyd’s season. Results showed that: The longitudinal and latitudinal variation in the differs in magnitude from one station to another within the same longitude due to the difference in the influence of the EEJ on them, which depends on how far from or near (latitudinal difference) they are to the EEJ band (confined within ±3°) wherein the EEJ current flows eastwards; The highest monthly longitudinal variation of EEJ is 92 at DAV and TIR during September equinox. This high amplitude at DAV andTIR compared with the other 9 stations, showed the presence of higher electric current (equatorial electrojet) in the ionosphere flowing over DAV and TIR. Thus the high magnitude could possibly be due to a greater width of the electrojet over thestations. The variation pattern for daily, monthly and seasonal variation were found to be similar; The magnitude of EEJ strength at stations within the same specified longitude differ where the EEJ strength at ILR is maximum with of 55 at about 1100 LT and maximum EEJ strength at DAV is 93 at about 1200LTwhich is the highest for the specified year; The possible factors responsible for the variation of EEJ is seen to be the ionospheric processes and physical structure such as wind and conductivity. The value peaks between 1000LT and 0200 LT for all the plots and varies with longitude and with latitude. The EEJ value for equinoctial months is seen to be higher than those of solstice months where the buildup flank is steeper in the morning hours than in the evening hours.

CHAPTER ONE

INTRODUCTION

1.1         Background to Study

The Earth's atmosphere is roughly 78 percent nitrogen, 21 percent oxygen, with trace amounts of water, argon, carbon dioxide and other gases. Nowhere else in the solar system can one find an atmosphere loaded with free oxygen, which ultimately proved vital to one of the other unique features of the Earth. The air surrounds the Earth and becomes thinner farther from the surface. Roughly 160 km above the Earth, the air is so thin that satellites can zip through with little resistance. Still, traces of atmosphere can be found as high as 600 km above the surface.

1.1.1 Classification of the Earth’s Atmosphere The earth’s atmosphere is generally divided into two broad sections namely; the lower and the upper atmosphere. The lower atmosphere starts from the surface of the earth and extends to about 40-50 km above the earth, depending on the latitude. The parameter of this region are what the meteorologists use in predicting atmospheric weather conditions. The earth’s upper atmosphere (ionosphere) starts from about 50 km above the earth and extends to about 600 km. This region is electrically conducting because of the partially ionized plasma that is produced by photo-ionization and this leads to the variation in the ionization level of the ionosphere. These variations can be regular and irregular. The atmosphere can be divided into layers based on its temperature. On the basis of temperature nomenclature; it can be divided into five layers or regions which are: troposphere, stratosphere, mesosphere, thermosphere and exosphere (Figure1.1). In terms of level of ionization, it can be divided into neutrosphere, ionosphere and protonosphere.

Troposphere

The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth (Figure 1.1). The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth. The troposphere is wider at the equator 16 km than at the poles 8 km and contains 75 percent of atmosphere's mass. Temperature and water vapor content in the troposphere decreases rapidly with altitude and the troposphere contains 99% of the water vapor in the atmosphere, it is in this layer that weather change phenomena takes place because water vapor plays a major role in regulating air temperature, due to its (Troposphere layer’s) ability for the absorption of solar energy and thermal radiation from the planet's surface. As sunlight enters the atmosphere, a portion is immediately reflected back to space, but the rest penetrates the atmosphere and is absorbed by the earth's surface. This energy is then remitted by the earth back into atmosphere as long-wave radiation. Carbon dioxide and water molecules absorb this energy and emit much of it back towards the earth again which helps to keep the average global temperature from changing drastically from year to year.