What are Solar Flares and How Do They Affect Us? (Part 1)
Geoscience Weekly: Exploring Earth's Phenomena II
This weekly newsletter delves into a different captivating topic from the world of geoscience, exploring Earth’s fascinating phenomena in bite-sized, easy-to-understand segments each week.
Monday 19th of February, this newsletter is the first part of the two stage newsletter about solar sun flares. Solar flares are strong powerful bursts of energy caused by an explosion on the surface of the Sun. There are five classes of solar flares: X, M, C, B, A-class with X-class solar flares being the biggest. Each class increases by a magnitude of 10 therefore an A-class solar flare would have no noticeable difference on Earth. Furthermore, within each letter class there is a finer scale from 1 to 9 with the exception of X-class flares which can go higher than 9. Why is this so important? Well, on the 9th of February 2024, NASA’s Solar Dynamics Observatory captured an X3.3 solar flare which is marginally smaller than the X5 solar flare observed on the 31st of December 2023. As shown in the image below, this X3.3 solar flare emitted electromagnetic radiation that directly impacts the ionosphere (charged upper layer of Earth’s atmosphere) consequently it can influence radio communications but we will get into more of that later.
What is a Solar Flare and What is a Sunspot?
A solar flare simply is huge explosion of electromagnetic radiation from the Sun. The bursts of electromagnetic radiation travel at the speed of light and manifest as a luminous region on the Sun in imaging, persisting for up to hours. Solar flares are different to sunspots and it’s important to not mix up these two phenomena even though they’re closely related. A sunspot is a dark area on the Sun’s photosphere (star’s outer shell from which light is radiated) which appears darker because it is cooler than other parts of the Sun’s surface — I use the term ‘cooler’ lightly. The sunspot is divided into two sections, the central umbra and the surrounding penumbra. The umbra is the darker region of the sunspot. The temperature of the umbra is between 3000–4500 K and the penumbra’s temperature varies around 5500–6000 K. Sunspots and accompanying solar flares are both formed via the Sun’s magnetic field and sunspots are cooler because the magnetic fields are so strong in these areas that they keep some of the heat within the Sun from reaching the surface. If you want to get into the detailed physics, sunspots are actually formed through manifestations in magnetic flux tubes.
Magnetic flux tubes are cylindrical structures in a magnetic field whose sides are parallel to the local magnetic field lines along its length. Effectively, electrical currents flow easily along magnetic flux tubes which is responsible for the ‘twisting’ effect of the magnetic field lines to form a flux rope. As seen in the image below the magnetic loops are flux rope and they’re also responsible for providing stability to the structure and for coronal mass ejections (CMEs) which we will get onto later.
As mentioned prior, the twisting effect of the flux ropes is very important in the formation of solar flares as the the magnetic fields on the Sun become tangled and they snap back releasing energy. Solar flares happen when fast-moving charged particles, mostly electrons, interact with the plasma surrounding the Sun. Scientists believe that magnetic reconnection (a process where magnetic fields rearrange) is responsible for this rapid acceleration of particles, leading to the intense energy release observed in solar flares. When the magnetic field on the Sun becomes twisted and not connected to its surroundings, it can suddenly burst outwards, carrying along material in a coronal mass ejection. This phenomenon often occurs in active regions of the Sun where magnetic fields are particularly strong. Now I've mentioned coronal mass ejections, lets look at those in more detail.
Coronal Mass Ejections (CMEs)
Firstly, coronal mass ejections are accompanied by solar flares released by the process of magnetic reconnection via flux ropes. So, a coronal mass ejection which I will refer to as CMEs from now on is an explosive outburst of plasma from the Sun. A CME contains particle radiation comprised of mostly protons and electrons along with magnetic fields which are stronger than magnetic fields found normally in solar wind. Solar wind is simply the Sun’s energy which isn’t visible made up of ionised plasma and particles escaping the Sun’s corona (the uppermost portion of the Sun’s atmosphere). The solar wind speed changes as it flows through space and influences the Earth’s magnetosphere. CMEs therefore can affect the Earth as when the CME collides with the Earth’s magnetosphere, the disturbance can send a particle radiation into the Earth’s atmosphere creating the auroras which I talk about in part 2 of this newsletter if you’re interested.
When are Solar Flares Likely to Happen?
Activity on the surface of the Sun, such as sunspots and solar flares, is dictated by the solar cycle. The solar cycle is the cycle that the Sun’s magnetic field goes through approximately every 11 years. Roughly every 11 years, the Sun undergoes a complete reversal of its magnetic field, resulting in a switch of its north and south poles known as a change in polarity. This occurs at the peak of each solar cycle due to the Sun’s inner magnetic dynamo re-organising itself. To understand a field reversal we need to quickly understand what the term current sheet means. The current sheet is an extensive surface extending outward from the Sun’s equator, generated by the Sun’s gradually rotating magnetic field inducing a small electrical current. The current sheet becomes very wavy and as the Earth orbits the Sun the Earth fluctuates in and out of the current sheet providing a barrier against cosmic rays (super-energetic particles that damage satellites). The sun’s polar magnetic fields will weaken all the way down to zero, then bounce back with the opposite polarity. Scientists still don’t fully understand the Sun’s magnetic flip however we can track the solar cycle. This is done by counting the number of sunspots at the beginning of a solar cycle, known as the solar minimum, or in the middle of the solar cycle, known as the solar maximum when the Sun has the most sunspots. The solar cycle 25 began in 2019 and will reach maximum in 2025 however this maximum is predicted to be weak, like solar cycle 24, which had only half the number of sunspots seen in solar cycle 23. Some solar physicists believe that the Sun may be in a period of inactivity like the Dalton minimum which was a period of reduced sunspot activity that occurred between roughly 1790 and 1830 named after English meteorologist John Dalton. The image below shows the evolution of the Sun in extreme ultraviolet light from 2010 through 2020.
How do Solar Flares Affect us on Earth?
In part 2 of this newsletter I go into more detail about CMEs and their relation to auroras. High energy particles and radiation produced by solar flares are dangerous to living organisms however on Earth we are protected from solar flares by the Earth’s magnetic field and atmosphere. Energetic particles (high-energy protons) and electromagnetic radiation (x-rays) are the most dangerous emissions from solar flares. The electromagnetic radiation is stopped by our atmosphere meaning it does not interfere with the Earth’s ionosphere. This is called x-ray absorption. X-ray photons are absorbed by encounters with atoms in the atmosphere and the energy of the x-ray goes into removing one of the electrons away from its orbit around the nucleus in either an oxygen or nitrogen atom. Known as photo-electric absorption, the photon is absorbed in the process of removing the electron from the atom reducing it’s impact on Earth. This process is demonstrated in the image below.
The energetic particles lead to proton storms which interfere with radio communication and damage satellites inducing short circuits in electrical circuits. For example, the precision of Global Positioning Systems (GPS) measurements can be degraded. This occurs because protons carry dangerous amounts of energy that can break chemical bonds. Effectively, when these energetic protons collide with the atmosphere they ionise the atoms and the molecules creating a layer of free electrons at the bottom of the ionosphere absorbing high frequency radio waves which makes radio communication difficult.
Conclusion
In conclusion, solar flares can be scary but it’s important to remember that unless our magnetosphere randomly vanishes then us mere humans are safe. Ultraviolet (UV) electromagnetic radiation from the sun plays more of a risk to human health than x-ray electromagnetic radiation from solar flares so make sure to wear sun cream. I hope you enjoyed learning about solar flares today and gained a deeper appreciation for the remarkable processes that shape our planet. If you want to learn more about geosciences come back every Monday for a new topic which is just as interesting. Check my profile for part 2 of this weeks newsletter.
Thank You
Thank you for reading, all information is taken from reputable sources and are linked below. All images are free to use under copyright laws.
RHESSI ‘ National Oceanic and Atmosphere Administration ‘ Chanda X-ray Observatory ‘ NASA