At this very moment, high above your heads, an invisible battle is going on between the Sun and Earth. It has been going on for billions of years, but you would hardly notice it unless you know what to look for.
Once in a while you might hear adults talk about seeing 'Northern Lights' in the skies over Alaska or Canada. Sometimes you will hear about satellites that mysteriously malfunctioned, or cell phones, pagers and TV channels that temporarily stopped working. You might come across old reports of shortwave radio signals being disrupted, electrical blackouts, or telegraph and telephone problems. You might even hear about radiation risks to astronauts, airline flight crews and passengers. You would have to be a master detective to sort out all these different things and see a pattern behind them. What could the Northern Lights and satellite problems possibly have in common? To appreciate how they all fit together we will need to look at an invisible side to Earth. This is a side that is usually not described in much detail in your textbooks.
In your textbooks you will probably have read about how the sun produces energy that heats Earth. You will have learned that Earth has a magnetic field like a toy magnet, and that this field lets us use compasses to find our way. You might also have learned about the Northern Lights and how they are caused by particles from the Sun that collide with atoms in the atmosphere to maks colorful dancing lights in the skies over Canada or Alaska. Scientists have studied each of these processes in space using satellites, and they have discovered that they form several important interconnected systems.
The Sun-Earth System:
Solar energy is transported to earth by radiation (light) and by particles of matter (solar wind). The radiation (called electromagnetic radiation) travels at the speed of light and takes only 8 minutes to reach Earth. The particles take much longer, sometimes many days, to arrive at Earth. These particles, mostly hydrogen and helium atoms, drag with them some of the sun's magnetic field. The sun can be stormy at times, and produces powerful explosions called solar flares (radiation) and coronal mass ejections (particles). When these arrive at Earth they provide the energy to drive many different kinds of phenomena - some of which we can see from the ground like the Northern Lights, but many phenomena are completely invisible unless you have the right kind of equipment to detect them.
The Magnetosphere System:
The Earth's magnetic field is created by currents in the core, and extends over one million kilometers into space. Inside this field, but outside Earth's atmosphere, there are particles trapped from the solar wind and from evaporation from the atmosphere. This collection of particles and fields is called the magnetosphere. When the solar wind collides with the magnetosphere, it imparts energy to to the particles causing stormy conditions in space. Some of the energized particles form their own currents and magnetic fields, while others flow into the atmosphere over the poles and cause the aurora. Because charged particles and magnetic fields affect each other strongly, scientists studying the mgnetospheric system have their hands full keeping track of all the things that can go on.
The Atmosphere System:
There is no true edge to the atmosphere, or a beginning to 'outer space'. The atmosphere just gets thinner and thinner. Even at altitudes of 10,000 kilometers - high above the orbit of the Space Station - there is still a lot of atmosphere left. The contact point or 'interface' between the magnetospheric system and the atmosphere reaches deeply into the atmosphere and ends at about the location of the ionosphere some 100 kilometers above the ground. The ionosphere is an electrically-charged layer of gas that we use to reflect radio waves between distant stations. Energy and currents flow from the magnetosphere into the ionosphere, and back out into the magnetosphere, like an invisible electrical current. Along the way, some of these currents can cause the Northern and Southern Lights (Aurora Borealis and Aurora Australis) in the polar regions of Earth. Meanwhile, lightning storms in the lower atmosphere cause electrical currents to flow into the upper atmosphere and ionosphere. The ionosphere receives energy both from the magnetosphere and from electrical storms in the lower atmosphere. This also means that the magnetospheric system can have some affect upon atmospheric electrical systems near the ground and in the lower atmosphere (troposphere). The sun also causes changes in the atmosphere above the ozone layer, as its ultraviolet light is absorbed and delivers energy to atoms there.
So, the Sun-Earth system exchanges energy with the magnetosphere of Earth through particles and fields. The sun also affects the upper atmosphere by delivering ultraviolet light energy to the regions above the ozone layer. These exchanges of energy and particles between the sun, the magnetosphere and the atmosphere, cause a complex series of changes to occur which result in many of the phenomena we learned about at the start of this essay.
Let's have a closer look at each of these three systems and see just how they work.