1.0 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.
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