TABLE OF CONTENTS
Title Page i
Certification Page ii
Approval Page iii
Table of Content vii
List of Tables xiii
List of Figures xii
List of Appendices xv
CHAPTER ONE: INTRODUCTION
- Background of the study 1
- The Earth’s atmosphere 2
- Troposphere 5
- Stratosphere 5
- Mesosphere 6
- Thermosphere 6
- Exosphere 7
- The ionosphere 8
- Geomagnetic field 11
- Geomagnetic field variation 14
- Quiet day variation 16
- Disturbed day variation 17
- Elements of geomagnetic field 17
- Cosmic rays 19
- Modulation of cosmic rays by geomagnetic field 21
- Effect of galactic cosmic ray on the Earth’s atmosphere 22
- Solar activity 23
- Sunspot 25
- Solar flares 26
- Coronal mass ejection 27
- Precipitation or rainfall in Nigeria 28
- Science of climate change 29
- Purpose of the study 31
- The Earth’s atmosphere 2
CHAPTER TWO: LITERATURE REVIEW
2.1 Solar activity 32
2.2 Earth’s magnetic field 35
2.3 Climate change 37
2.4 Cosmic rays 37
2.5 Cloud cover 38
2.6 Air temperature 39
2.7 Rainfall 40
CHAPTER THREE: SOURCES, THEORY AND METHODS OF DATA ANALYSIS
3.1 Sources of data 43
3.1.1 Source of data for sunspot number 43
3.1.2 Source of data for geomagnetic aa index 43
3.1.3 Source of data for cosmic rays 43
3.1.4 Source of data for cloud cover 43
3.1.5 Source of data for rainfall 44
3.1.6 Source of data for air temperature 44
3.2 Theory of method of data analysis 44
3.2.1 Theory of method of analysis of sunspot number 44
3.2.2 Theory of method of analysis of geomagnetic aa index 45
3.2.3 Theory of method of analysis of cosmic rays 46
3.2.4 Theory of method of analysis of cloud covers 47
3.2.5 Theory of method of analysis of rainfall data 48
3.2.6 Theory of method of analysis of air temperature 49
3.3 Method of data analysis 49
3.3.1 Bivariate analysis 49
3.3.2 Spearman’s rank correlation coefficient 50
- Power spectral density (PSD) analysis 50
3.3.4 Method of analysis of sunspot number 51
3.3.5 Method of analysis of geomagnetic aa index 51
3.3.6 Method of analysis of cosmic rays 53
3.3.7 Method of analysis of cloud covers 53
3.3.8 Method of analysis of rainfall 53
3.3.9 Method of analysis of temperature
This study investigates the influence of solar activity and geomagnetic activity on climate change over Nigeria, in order to ascertain their impact on the observed climate change in the country. Data of sunspot number and geomagnetic aa index were obtained from World Data Center and National Centers for Environmental Information. The data spanned from 1950 – 2012 and 1950 – 2010 respectively. Pressure corrected hourly cosmic rays data were obtained from Thule Neutron Monitor Station (76.5o N, 68.5o W, 26.0 m) with the geomagnetic cut-off rigidity of 1.0 GV and Haleakala Neutron Monitor Station (20.71o N, 156.17o W, 3052 m) with the geomagnetic cut-off rigidity of 13.3 GV. The data span for 56 years (1957 – 2012) and 16 years (1991 – 2006) respectively. Monthly mean global cloud cover data for high, middle, and low clouds were obtained from the International Satellite Cloud Climatology Project (ISCCP)-D2 datasets, for a period of 27 years (1983 – 2009). Monthly mean daily rainfall, minimum and maximum temperature data for 20 synoptic stations in Nigeria were obtained from Nigeria Meteorological (NIMET) Agency. The data span for 63 years (1950 – 2012). Descriptive, bivariate and spectral analyses, as well as Mann-Kendall trend test were employed in analyzing the data. These analyses were executed using Microsoft Excel, XLSTAT, MATLAB, and SPSS. The standardized decadal rainfall and temperature anomalies from 1950 – 2010, using 1981 – 2010 as the based period were presented using ArcGIS software. Results reveal that sunspot number varies in opposite direction with galactic cosmic rays (GCRs) based on the 11-year solar cycle. This was also observed in the variations of aa index with GCRs. From the correlation analysis, sunspot number and aa index were strongly but negatively correlated with cosmic rays with correlation coefficients of -0.843 and -0.686 respectively. This indicates that solar and geomagnetic activities modulate cosmic rays penetrating into the Earth’s atmosphere. The variations of GCRs with cloud cover show that cosmic rays have good correlation with low cloud cover from 1983 – 1995, in contrast to high and middle cloud cover as observed by other researchers. On the other hand, in the recent quiet period of solar cycles, cosmic rays have good correlation with high and middle cloud covers in contrast to low cloud cover. This contradicts the previous findings by some authors. The variations of cloud covers with rainfall and temperature show that changes in cloud covers are associated with changes in rainfall and temperature. The air temperature was observed to increase in the period under study which could be associated with global warming. Similarly, rainfall was also observed to be on the increase. This was confirmed from the results obtained using Mann-Kendall trend test. These are evidence of climate change. The proposed GCR – cloud hypothesis was yet to be established in this study, hence, the connection between solar and geomagnetic activities with climatic parameters is yet to be fully confirmed. However, results of the spectral analysis reveal that Schwabe, Hale and Gleissberg cycles, as well as some atmospheric phenomena (such as quasi-biennial oscillation), were detected in geomagnetic, solar activity and climatic parameters in Nigeria. This implies that signature of solar and geomagnetic activities effect exists on rainfall and temperature, which could be linked to the observed climate change in Nigeria. Hence, we suggest that apart from anthropogenic activities, solar and geomagnetic activity, as well as atmospheric phenomena might play important role in climate change observed in Nigeria.
1.1 Background of the Study
It is a clear fact that the Earth’s climate has changed in the past, still changing at present and is expected to change in the future. Information from tree rings, ice layer, marine deposits, e.t.c. as documented in historical as well as in geological records have shown that the Earth’s climate is constantly changing. In addition to natural climate changes, the risk of human influence on climate has recently been seriously considered by the Intergovernmental Panel on Climate Change (IPCC). The reasons for these changes, however, have always been the subject of discussions and are still not well understood.
It is obvious that the effect of this changes is manifested more strongly now than ever before. The effects of climate changes (such as loss of sea ice, accelerated sea level rise, global temperature rise, extreme events, oceans rise, e.t.c) that scientists had predicted in the past, that could result from global climate change is more severe now (National Academy of Sciences and Royal Society, 2014).
Climate change is affected by many factors: the influence of continental drift, variations in solar intensity, volcanism, the impact of meteors and comets, changes in the Earth’s orbital parameters, ice acculations and depletion, variations in oceans circulations and chemistry, changes in terrestrial and aquatic life, and changes in atmospheric composition and circulation.
The effects of natural factors such as geomagnetic activity, volcanic activities, e.t.c. and primarily of the solar activity and the associated variation of solar radiation and fluxes of galactic cosmic rays (GCRs), as well as the effect of the geomagnetic dipole variations on the climate processes, are important for understanding the physical causes of modern climate changes (Dergachev et al., 2004).
Studies have shown that solar variability has played a crucial role in the past climate changes. Sunspot numbers have been generally used as a reliable parameter to measure solar activity (Tiwari et al., 2011). Controversy, however, remains over what levels of solar variability are required to generate significant climate change and what mechanisms are involved (Laut, 2011).
The Earth’s magnetic field varies over many time scales leading to irregular variations known as geomagnetic activity or storms. This is due to extreme events, such as coronal mass ejections from the Sun. Recent studies have shown that past climate changes may have been connected with variations in the Earth’s magnetic field elements at various time scales (Dergachev et al., 2012).
The IPCC (2013), reported that human impact has been the dominant cause of observed climate change. Since changes in climate have significant implications for present lives, for future generations and for ecosystems on which humanity depends, it continues to be a subject of an active study area and public debate.
1.2 The Earth’s atmosphere
The Earth’s atmosphere is a layer of gases surrounding the planet Earth. It has a mass of about 5.15 x 1018 kg, three-quarters of which is within about 11 km of the surface (Lutgens and Tarbuck, 1998). The atmosphere has no definite upper limit, however; it becomes thinner and thinner with increasing altitude, eventually merging with empty space, which surrounds all the planets. The study of the Earth’s atmosphere and its processes is called atmospheric science (aerology).
The major components of air are nitrogen, oxygen, and argon. These constitute the major gases in the atmosphere. Water vapour, dust particles, ozone, and other trace gases are also present in a small percentage. They can have significant effects on weather and climate.
A vertical profile of the atmosphere reveals that it is divided into a series of layers or “spheres”, which are separated by transition regions or “pauses”. Each layer may be defined in a number of ways: by the manner in which the air temperature varies through it, by the gases that comprise it, or even by its electrical properties. The layer of the Earth’s atmosphere based on temperature gradient is shown in Figure 1.1.
Air pressure and density decrease with height above the Earth – rapidly at first, then more slowly. Air temperature, however, has a more complicated vertical profile. Air temperature normally decreases from the Earth’s surface up to an altitude of about 11 km. This is due primarily to the fact that sunlight warms the Earth’s surface, which in turn, warms the air above it. The rate at which the air temperature decreases with height is called the temperature lapse rate. The average lapse rate in this region of the lower atmosphere is about 6.5 oC for every 1000 km or about 3.6 oF for every 1000 ft rise in elevation. Occasionally, the air temperature may actually increase with height, producing a condition known as a temperature inversion. So the lapse rate fluctuates, varying from day to day and season to season (Ahrens, 2003).