CHAPTER ONE
1.1 BACKGROUND OF THE STUDY
Ozone depletion and geomagnetic storm are among the most severe phenomena that disturb the world today. When there is ozone depletion, harmful ultraviolet (UV) radiations from the sun penetrates into the earth and affect human health and ecosystem in general. Ozone depletion and geomagnetic storm generally contribute to climate change. Some research works have suggested that geomagnetic storm is always associated with ozone variation in the mid-latitude. Until now, no scientific work has been carried out to ascertain this fact. Also, researchers have hitherto considered the zonal wind to be weak at the tropics (where Nigeria is located) hence, dynamical processes around the low and mid-latitude have not been adequately considered.
As a secondary pollutant, ozone is not emitted directly but is generated in the atmosphere through a complex series of chemical reactions initiated by absorption of solar energy (Seinfeld and Pandis, 1998 J.H. Seinfeld and P.J. Pandis, Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley, New York (1998).Seinfeld and Pandis, 1998). The atmospheric wind influences the time of occurrence of the daytime ozone maximum. Increase in air temperature as a result of intense solar radiation causes an increase in the variation of total ozone. This is because ozone in the stratosphere is created and destroyed primarily by ultraviolet (UV) radiation from the sun. That is; ozone is formed when oxygen molecules absorb UV radiation and split apart into two oxygen atoms (O), which combine with other oxygen molecules (O2), to form ozone molecules (O3). Ozone is also broken apart as it absorbs UV radiation. In this way, UV helps sustain the natural balance of ozone in the stratosphere, while ozone in turn absorbs UV, protecting life on earth from these harmful radiations.
The solar chromospheric activity in the ultraviolet region is of great importance to our understanding of both the physical properties of the sun as a star, and of the solar influence on the earth’s stratospheric chemistry. Okeke (2012) noted that how sun’s magnetic field connects with the geomagnetic field determines how solar activity affects the earth. The interaction between the solar plasma and the earth’s magnetic field causes a number of current systems to develop in the magnetosphere during a magnetic storm. In other words, compression of the magnetosphere by plasma causes development of magnetopause current and ring current systems which are the main current systems responsible for a typical magnetic storm recorded at mid- and low-latitudes. When the solar activity is high both solar UV radiation and ozone concentrations are high.
The atmospheric activities that cause ozone variations are photochemical processes and dynamical processes. The former refers to the production and destruction of ozone and it is driven by solar ultraviolet (UV) photochemistry in the upper stratosphere. The later refers to how ozone is transported from one location to another by winds and large scale circulation patterns in the atmosphere. Atmospheric angular momentum (AAM) is a fundamental circulation index used in representing and measuring the dynamic state of the whole circulation of the atmosphere and climate (Peixoto and Oort, 1992; Abaraca del Rio et al., 2000; 2003). It has been observed that much of the historic development of modern meteorology is connected with the study of how atmospheric momentum is maintained locally or transported from one region to another and how it is exchanging momentum with the oceans and solid earth (Peixoto and Oort, 1992). The main contributions to the axial AAM components are the global zonal winds in the troposphere and stratosphere. AAM is highly correlated with changes in length of day (LOD), a measure of the earth’s rotation rate (Eubanks, 1993).
Nigeria, being in the tropics and where not much research work in the depletion of ozone and consequences of zonal winds, solar activity phenomenon together with geomagnetic storms on the ozone variation has been investigated, it becomes crucial that this study be carried out in Nigeria. Hence, in our study, an attempt will be made to study the effect of this interaction; zonal winds, solar activity and magnetic storm influence over six stations namely; Sokoto (13.030N 05.270E), Maiduguri (12.000N 13.330E), Abuja (09.080N 07.050E), Ikeja (06.420N 03.450E), Port-Harcourt (04.850N 07.02oE) and Enugu (06.430N 07.480E), in the tropics – Nigeria (West Africa) as a case study; this was selected according to the six (6) geo-political zones in Nigeria to ensure even distribution. Isikwue (2009) suggested that effects of geomagnetic storms on ozone in the tropical latitudes be carried out, since Mitra (1947) noted that increase in the ozone values in the middle atmosphere was always associated with geomagnetic storms. Since then, no research work has been carried out to investigate the extent or validity of Mitra’s finding; it is on this note and on existing controversies and inconsistencies that this work becomes very necessary.
1.2 THE EARTH’S ATMOSPHERE
The atmosphere that is very essential for all life forms on earth is a mixture of many gases. The three major components of ordinary air near the surface are nitrogen (76.9%) and oxygen (20.7%) with the next largest component being water vapor (1.4%). Many gases in the atmosphere are capable of chemical reactions. Some of those present in trace amounts may form combinations that are commonly considered to be pollutants. These and other potentially harmful gases are monitored in many urban areas by State Health departments or by Environmental Protection Agency, these include nitrogen oxides, sulfur dioxide, carbon monoxide, methane, ozone, and ammonia (Eagleman, 1980). The atmosphere protects life on earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
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