ABSTRACT
The Sun provides nearly all of the energy that drives the Earth’s climate system. Although understanding the effects of solar variability on Earth’s climatic change remains one of the most puzzling questions that have continued to attract attention of scientists. The Sun has been observed to vary on all time-scales and there is increasing evidence that this variation may have an effect on the Earth’s climate. Scientists have been attempting to establish on the quantity of solar energy that illuminates the Earth and what occurs to the energy once it gets through the atmosphere. The climate response to these variations can be on a global scale but understanding the regional climate effects is more difficult. In this project research, we study the correlation between solar variability and the Earth’s climatic changes over the last 17 years. We make use of solar data from Solar Radiation and Climate Experiments (SORCE) and climate data from Climate Research Unit (CRU). In order to observe how these changes have occurred, analysis of the data was done using GNU-plot and python to show the trend. As an outcome, from the results we explore for the possible correlation linking the solar variability and the Earth’s climate change over the 17 years period. Our results show a linkage in the change of the climate factors which can be attributed to, but not completely to the solar variability. Further advances in understanding of the solar variability and its effect on climate are recommended from the ongoing acquisition of high-quality measurements of climate and solar variables. This knowledge is of importance as it can be used to in estimating the past and the future of solar behavior and climatic response.
TABLE OF CONTENTS
DECLARATION i
DEDICATION ii
ACKNOWLEDGEMENTS iii
ABSTRACT iv
TABLE OF CONTENTS v
LIST OF FIGURES viii
LIST OF ABBREVIATIONS/ ACRONYMS AND SYMBOLS ix
CHAPTER ONE
INTRODUCTION
1.1 Background information 1
1.2 Problem statement 4
1.3 Research Objectives 5
1.3.1 Main objective 5
1.3.2 Specific objectives 5
1.4 Justification and significance 5
CHAPTER TWO
LITERATURE REVIEW
CHAPTER THREE
THEORETICAL BACKGROUND
3.1 The Sun as a blackbody 11
3.2 Solar Luminosity 12
3.3 Effective temperature 13
3.4 Radiative forcing 15
3.5 Atmospheric gas forcing 16
3.6 Role of the middle atmosphere 16
3.7 Effect of energetic particle precipitation (EPP) on the atmosphere 17
3.8 Bottom-up and Top-down mechanisms 18
CHAPTER 4
METHODOLOGY
4.1 Introduction 19
4.2 Source of data 19
4.3 Data acquisition and analysis 20
4.4 Data smoothing 20
4.5 Linear regression 21
CHAPTER FIVE
RESULTS AND DISCUSSIONS
5.1 Introduction 22
5.2 Solar variability results 22
5.2.1 Total Solar Irradiance (TSI) 22
5.2.2 Solar Effective Temperature 24
5.2.3 Computed Solar Luminosity 25
5.2.4 Sunspot Numbers 27
5.2.5 Spectral Solar Irradiance (SSI) 29
5.3 Climate variability results 29
5.3.1 Carbon dioxide concentration 29
5.3.2 Global temperature anomalies 31
5.3.3 Global temperature anomalies of the northern hemisphere 34
5.3.3 Global temperature anomalies of the southern hemisphere 35
5.3.4 Global temperature anomalies of both hemispheres 35
5.4 Solar variability and climate change 36
5.4.1 TSI and Sunspot numbers 36
5.4.2 Global temperature anomaly and carbon dioxide concentration 37
5.4.3 Temperature anomalies and TSI 39
CHAPTER SIX
CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions 40
6.2 Recommendations 40
REFERENCES 41
LIST OF FIGURES
Figure 1: Structure of the Sun (Source: The Sun Today- solar facts and space weather) 2
Figure 2: Spectral Irradiance of the Sun against wavelength (Source: Science Direct) 12
Figure 3: A graph of total solar irradiance over the 17 years 22
Figure 4: A graph of total solar irradiance over the 17 years fitted with polynomials. 23
Figure 5: A graph of computed effective temperature at 1AU 24
Figure 6: A graph of computed effective temperature at 1AU fitted with polynomial. 25
Figure 7: A graph of computed solar luminosity at 1 AU 26
Figure 8: A graph of computed effective temperature at 1AU fitted with polynomial. 27
Figure 9: A graph of sunspots numbers over the 17 years. 28
Figure 10: A graph of Spectral Solar Irradiance against the wavelength range 29
Figure 11: A graph of carbon dioxide concentration for the years 2003-2017 30
Figure 12: A graph of carbon dioxide concentration for the years 2003-2017 fitted with linear fit.. 31
Figure 13: A graph of global temperature anomalies over the 17 years. 32
Figure 14: A graph of global temperature anomalies with linear fit 33
Figure 15: A graph of global temperature anomalies of the northern hemisphere for the 17 years with linear fit 34
Figure 16: A graph of global temperature anomalies of the southern hemisphere for the 17 years. 35
Figure 17: A graph of global temperature anomalies of both hemispheres for the 17 years. 36
Figure 18: A graph showing the comparison TSI and Sunspot number 37
Figure 19: A graph of global temperature anomalies against carbon dioxide concentration. 38
Figure 20: A graph of global temperature anomalies and the TSI 39
LIST OF ABBREVIATIONS/ ACRONYMS AND SYMBOLS
TSI – Total Solar Irradiance SSI – Spectral Solar Irradiance SEP – Solar Energetic Particle
SIM – Spectral Irradiance Monitor
SOLSTICE – Solar Stellar Intercomparison Experiment SORCE – Solar Radiation and Climate Experiment CME – Coronal Mass Ejections
UV – Ultraviolet
HEP – High Energy Particle GSM – Grand Solar Minimum SEP – Solar Energetic Particles GCR – Galactic Cosmic Rays
CHAPTER ONE
INTRODUCTION
1.1 Background information
We live on a planet, Earth, which is part of the solar system that is Sun centered. The Sun is the main originator of energy that sustains life on Earth. It is almost an ideal sphere of hot plasma heated to blaze as a result of the nuclear fusion reactions taking place at the core hence radiating energy as infrared radiation and visible light. The Sun is known to have formed through self-gravitational collapse of a cloud of dust and gas. Majority of this matter collected in the middle via self- gravitating, as the rest flattened into an orbiting disk that formed the solar system.
The Sun has a diameter of approximately 1.39 million kilometers, or its diameter is 109 times that of the Earth, it has a mass that accounts for around 99.86% that of the solar system and it is around 330,000 times that of the Earth. It has a composition of approximately 70% hydrogen, 28% helium and other smaller quantities of heavier elements which include carbon, oxygen, iron and neon. The Sun’s age is approximately 4.6 billion years and has a luminosity of 3.828×1026 Watts. It rotates about once every 27 days on average, with the poles rotating every 24 days and the equator every 30 days.
The Sun’s structure comprises of the following layers: 1) The core, which is the innermost layer occupying between 20 to 25% of the Sun’s radius, where temperatures (approximately 15 million Kelvin) and pressure (approximately 26.5 petapascals) are sufficiently high for nuclear fusion to occur. The nuclear fusion produces energy that makes the core becomes rich in helium. 2) The radiative zone, this is the layer just after the Sun’s core. Energy transfer in this layer occurs by means of radiation. 3) Tachocline, which is the region that creates the boundary linking the radiative zone and the convective zone. 4) Convective zone, which is the layer between the Radiative zone and a close point to the visible Sun’s surface. In this layer, the temperatures are cool such that convection can take place and this forming the fundamental method of extrinsic heat transfer. 5) The photosphere, this is the deepest section of the Sun, and can be directly observed. The Sun is made up of gas and it lacks a distinctly defined surface. The visible part is categorised into the photosphere and the atmosphere. The atmosphere is a gaseous ring of light surrounding the Sun and is made up of four parts, which are the transition region, chromosphere, the heliosphere and the corona. This layer is most visible during a solar eclipse. Figure 1 shows the structure of the Sun.
Figure 1: Structure of the Sun (Source: The Sun Today- solar facts and space weather)
Each second, the Sun’s core turns four million tons of mass to energy by fusing around 600 million tons of Hydrogen to Helium, resulting in new neutrinos and solar radiation. The produced energy may take anywhere from 10,000 years to 170,000 years to exit the Sun’s core, this forms the origin of its heat and light. The Sun has converted nearly 100 times the Earth’s mass into energy so far, accounting for around 0.03 percent of the total mass of the Sun. It will take the Sun around ten billion years in its main sequence stage, powered by nuclear burning of Hydrogen.
The Sun’s magnetic field changes over its surface, in both location and time with the prominent variation being the solar cycle that has a period of 11years. Sunspots are dark spots appearing on the surface of the Sun that correlate to the concentration of the magnetic field lines, which obstructs convective heat transmission from the solar interior. The Sun's activity changes in a relatively uniform 11-year cycle, which is quantified with regard to fluctuations of the number of detected sunspots. The terms "solar minimum" and "solar maximum" refer to periods when the number of sunspots is at its lowest and highest. During solar minimum, the visible sunspots are few and occasionally none is visible at all. Sunspots tend to appear around the solar equator as the solar cycle approaches its ceiling. The Sun’s magnetic field flips during its solar cycle when the sunspot cycle approaches climax. The quantity of solar ejection and radiation of solar materials, the size and number of sunspots, coronal loops and solar flares together show a harmonized variation from active-to-quiet-to active once more with 11-years periods. The 11-year periodic sunspot cycle is half of the 22-year Leighton dynamo cycle, which agrees with an oscillating energy interchange between poloidal and toroidal magnetic fields.
The solar magnetic field stretches out far beyond the Sun itself. The interplanetary magnetic field (IMF) is created when the magnetic field of the Sun is transferred into space by the electrically conducting solar wind plasma. The movement of the plasma particles takes place along magnetic field lines in an ideal magnetohydrodynamics.
The magnetic field of the Sun causes many effects known as the solar activity. The coronal mass ejections (CME) and solar flares are most likely to occur at sunspot groups. At the photosphere surface, there is an emission of slow-varying supersonic streams of solar wind from the coronal holes. Both supersonic jets of solar wind and the coronal mass ejections carry interplanetary magnetic field and plasma to the solar system.
Extended changes in the number of sunspots are conceived to be related to long term variability of solar irradiance, which could affect the climate of the Earth in the long-term. For instance, in the 17th century, few sunspots were observed and the solar cycle seemed to have ceased for a number of decades in the time of the Maunder Minimum, which took place at the same time with the little Ice Age era when Europe encountered remarkably low temperatures. This phenomenon has steered exploration on the basis of understanding the concept of solar cycle together with the role of the sunspots, faculae and network of magnetic field features.
Solar variability is defined as the changes in the solar activity, such as the change in the amount of energy radiated by the Sun, and change in solar wind. Solar irradiance on the other hand refer to the output of light energy per unit area perceived from the Sun, and is evaluated in the wavelength range. It is expressed in Watts per square (W/m2) in its SI units. It can be determined either at the Earth’s surface following dispersion and absorption by the atmosphere or it can be determined in space. The Sun’s height overhead the horizon, the tilt of the measuring surface, and weather conditions all influence the solar irradiance at the surface of the Earth. Both animal behavior and plant metabolism are influenced by solar irradiation. The measured categories of solar irradiance include; Total solar irradiance (TSI), which is an estimate over all wavelengths of the solar power on top of the Earth’s atmosphere per unit area. The TSI is calculated by measuring the arriving radiation perpendicularly. Solar constant refers to a traditional measurement of average total Sun radiation at one astronomical unit (AU) distance. Total solar irradiance varies gradually on decadal and longer timescales. Spectral Irradiance is the irradiance of a surface per unit wavelength or frequency and is expressed in Watts per square meter per nanometer (W/m2/nm).
The Earth is exposed to the various radiations from the Sun and its temperature is controlled by the balance between the warmth from the radiation and the shielding by its atmosphere. Any changes in the Sun's radiative output are bound to have an effect on the Earth's atmospheric energy balance and hence may have possible effect on the Earth's climate by changing the stratospheric chemistry leading to disturbance of the balance in the ozone destruction and production (Solanki, 2002). The hunt for solar cycle indication among the terrestrial temperature data, although minute, persists to inspire much exploration in the area, and two basic mechanisms have been modelled so far. The first mechanism is the bottom-up total solar irradiance path, and the second avenue is the top-down mechanism which includes absorption of UV radiation in the stratosphere (Board, 2012).
The influence of the Sun has been acknowledged since the prehistoric time when the Sun was perceived of by some cultures as god. Solar calendars are based on the orbit of the Earth around the Sun and its synodic rotation, including the Gregorian calendar, which is the most widely used calendar today.
1.2 Problem statement
Climate change is becoming a great concern to humanity because it affects activities such as farming among others. Climatic drift may influence weather patterns in that, areas which previously received regular rainfall may as well develop drought. Solar activities are the main cause of climatic change on Earth. Hence, any fluctuations in the solar output are likely to influence the climate on Earth.
In this project research, we carried out a study on the nature of the Sun's variability during the last 17 years using data collected by the Solar Radiation and Climate Experiments (SORCE) (https://lasp.colorado.edu/home/sorce/data/ ) and assess the possible effects of the resulting variability on the Earth's climate using data of the Total Solar Irradiance (TSI), the Spectral Solar Irradiance (SSI) and of climate change collected between years 2003 to 2020.
1.3 Research Objectives
1.3.1 Main objective
The main objective of this research project is to carry out a study on the observed solar variability for the last 17 years as well as to explore the possible link relating the Sun's variability and the Earth's climate change using solar activity data from SORCE and climate data from Climate Research Unit (CRU).
1.3.2 Specific objectives
The specific objectives of this research are:
i) To acquire the relevant data from Solar Radiation and Climate Experiments (SORCE) and Climate Research Unit (CRU) for periods 2003 and 2020.
ii) To import the data into GNU-plot and Python and analyze the characteristics.
iii) To fit the results for variability with theoretical models.
iv) To explore the possible correlation linking solar variability and Earth’s climate change over the past 17 years.
1.4 Justification and significance
The question of how solar changes and the associated solar terrestrial effects affect the Earth's climate change remains an important unsolved problem in solar Physics and climate change research. Understanding and forecasting of the solar variability is one of the biggest challenges. This study has received a lot of public interest since dependable approximates of the effect on global surface temperatures is required to reduce uncertainty in the relative significance of human activity as a possible clarification of climate change. This study is of much significance as it may be used to predict the past and future solar variability and climatic response so that the human and natural signals may be untwined in the observational record and hence more dependable estimates can be made. The analysis and computation of solar irradiance is of importance in the forecasting of energy production of solar power plants, cooling and heating of buildings as well as the climate modeling and weather forecasting.
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