I periodically go back through past articles to make sure I am not revisiting the same topics too often.
Looking back over the last 22 years, I noticed that every three years or so I tend to circle back to what I call my weather school articles. These are a series of pieces I originally wrote in 2008, designed to walk readers through many of the topics typically covered in a first-year meteorology or atmospheric science course.
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These are courses I taught for several years, and rather than having you work through a textbook, I try to distill the main concepts and present them in a straightforward, easy-to-understand way. The added bonus is that you do not have to study, write exams or pay for a university course, yet you still get the core ideas.
Start with the sun
To begin understanding how and why we experience weather here on Earth, we need to start at the source of nearly all the energy that drives our atmosphere: the sun. It is considered an average star by astronomical standards and is estimated to be about halfway through its expected lifespan of roughly 12 billion years. While it is relatively small compared to many other stars in the universe, it dominates our solar system, containing about 99 per cent of all the matter within it. The remaining one per cent is made up of the planets, moons, asteroids, comets and other assorted debris orbiting around it.
Most of the sun’s mass consists of hydrogen, the simplest and most abundant element in the universe. Deep inside the sun, the enormous pressure created by this mass raises temperatures to extreme levels. When conditions become hot enough, hydrogen atoms begin to fuse together to form helium. This process, known as nuclear fusion, releases tremendous amounts of energy in the form of heat.
Fusion has been occurring inside the sun for billions of years, and there is enough hydrogen fuel available for it to continue for billions of years more, so there is no reason to worry about the sun suddenly running out of energy.
Not surprisingly, given that our sun is a relatively stable and unremarkable star, the fusion of hydrogen into helium has been occurring at a remarkably steady rate. While scientists have observed very slight variations in the sun’s energy output over time, these changes are extremely small when compared to its overall energy production and are barely noticeable on human timescales.
As most of us already know, the sun supplies Earth with nearly all of its heat energy. The next logical question is how that energy actually makes its way from the sun to Earth. After all, space is a cold, near-empty vacuum, so energy cannot be transferred by conduction or convection. Instead, the energy arrives in the form of radiation — more specifically, electromagnetic radiation.
Sunlight science
For many people, the word radiation immediately brings to mind nuclear accidents, weapons, or dangerous invisible rays that cause illness. So how can radiation be responsible for sustaining life on Earth? The answer is that radiation comes in many different forms. Some types are harmful to organic life, while others are completely harmless and, in fact, essential. To understand the difference, we need to take a closer look at the electromagnetic spectrum.
If you examine the electromagnetic spectrum, you will quickly recognize several familiar forms of energy. At the low-energy end of the spectrum are radio and television waves. Near the middle lies visible light, the energy that allows us to see the world around us. At the high-energy end of the spectrum are more dangerous forms of radiation, such as ultraviolet radiation, X-rays and gamma rays.
All of these forms of radiation are simply waves of energy, and the amount of energy they carry depends on the length of their wavelength. Long wavelengths, such as radio waves, often measuring around a metre in length, carry relatively little energy. As wavelengths shorten, energy levels increase, moving through infrared and into the visible portion of the spectrum. Visible light waves are extremely small, measuring roughly 400 to 700 billionths of a metre.
Visible light
Given how hot the sun is, it might seem reasonable to assume that most of its energy would be emitted as high-energy radiation such as ultraviolet, X-rays or even gamma rays. While the sun does emit energy across the entire electromagnetic spectrum, the majority of the radiation that reaches Earth comes in the form of visible light. This turns out to be extremely important, as visible light can pass through the atmosphere relatively easily and be absorbed at Earth’s surface.
One of the most remarkable properties of electromagnetic radiation is its ability to travel through the vacuum of space and reach Earth. Once it arrives, that energy is either reflected back into space or absorbed by the surface and atmosphere, where it is converted into heat.
When we take Earth’s distance from the sun into account and calculate how much of the sun’s total energy actually reaches our planet, the result is surprisingly small — only about one two-billionth of the sun’s total energy output. Despite this, the amount of energy added to Earth’s system is enormous. On average, Earth receives approximately the equivalent of all the energy used by humanity in a entire year each hour.
Next time we’ll look at another related topic from weather school: insolation, the incoming radiation received by Earth, and the concept known as the solar constant.
