C H A P T E R
N ° 12
Space Weather and the Aurora
The aurora is a phenomenon created when activities happening on the Sun interact with a celestial body containing an atmosphere. The interaction can cause colorful and vibrant light only visible to the naked eye at night. The aurora is, thus, a phenomenon that can be experienced on multiple planets and moons in our solar system.
Image Credit: Lucas Marcomini: Showing the aurora.
Image Credit: Lightscape: Showing the aurora.
The Aurora on Earth
On Earth, the aurora takes place in Earth’s thermosphere and can be seen around the North Pole - also called the Aurora Borealis (i.e., Northern lights) - and the South Pole – also called the Aurora Australis (i.e., Sothern lights) at night. Sometimes it can even be seen around the equator of Earth. This is mostly in cases where strong and severe space weather events occur. Yet, even though this phenomenon is best experienced at night, it is actually caused by Earth-directed solar activities interacting with the sunlit-side of Earth. - [read more about space weather and Earth’s atmospheric layers in SR Hoplon’s previous blog].
The origin of Auroras
Most space weather events can cause the auroras. However, the most vibrant and active ones are caused by geomagnetic storms created by Coronal Mass Ejection (CME). When a Coronal Mass Ejection (CME) is created it bursts mass projected from the Sun’s corona out into the solar system. The mass contains billions of tons of plasma which comprises electrically and magnetically charged particles. If Earth-directed, this charged mass can interact with Earth’s magnetic field.
When interacting, the field lines can trap the particles, making them travel through the field lines and bounce back and forth from one of Earth’s geomagnetic poles to the other. As they bounce around, the risk of the particles interacting with particles in Earth’s atmosphere increases. This is because the magnetic field lines of Earth are highly inclined – almost vertical – at the Earth’s poles, enabling the particles to penetrate deep into the upper atmosphere. If the particles collide with already present atoms/molecules within the Earth’s atmosphere, they release energy as light. It is this light and disturbance we on Earth experience as the aurora.
However, not all Coronal Mass Ejections (CMEs) cause the vibrant auroras. The Coronal Mass Ejections (CMEs) have to have a certain magnitude (i.e., reach a certain level of intensity). Furthermore, the magnetic field within the plasma, additionally, has to have a certain orientation. The Earth has a magnetic field similar to a bar magnet. Something similar to that can be found and is embedded within the plasma bursting out of the Sun. Yet currently, the magnetic orientation (i.e., north or south pole) of the plasma is unknown until the Coronal Mass Ejection (CME) reaches a sensor on a satellite located very close to Earth.
Knowing the orientation of the magnetic field of the plasma it is very critical, as it determines the magnitude of the event that will occur around and on Earth. This is because opposites attract. If the magnetic field in the plasma is in the same direction of that of Earth’s, most of the particles will get repelled by Earth’s magnetic field. Yet, if it is the opposite, the magnetic field of Earth and that of the plasma will connect (i.e., causing magnetic reconnection). As they connect, the particles can travel through Earth’s magnetic field and get released into the atmosphere at the Earth’s poles and create the aurora.
If a magnetic reconnection occurs and the plasma contains particles with high energy levels, the aurora may even be seen as far as the equator. This is because the Earth’s magnetic field is the strongest at its poles but weakest at its equator.
Image Credit: NASA: Cartoon showing magnetic reconnection and the Aurora.
What causes the colors?
The different colors of the aurora depend on the gas that is being excited by the electrons and the amount of energy that is being exchanged. The colors green, yellow, and red can be experienced if the interaction occurs with Oxygen, whereas blue, purple, and pink can occur due to interactions with Nitrogen.
Source
A.K. Gwal et al. (2021): ”Chapter 15 – Space Weather Phenomenon of Polar Ionosphere Over the Arctic Region”. Understanding Present and Past Arctic Environments. Elsevier. Pp. 325-341. DOI: https://doi.org/10.1016/B978-0-12-822869-2.00016-5.
Peter I. Y. et al. (2013): ”Impact of cosmic rays and solar energetic particles on the Earth’s ionosphere and atmosphere”. J. Space Weather Space Climate. Vol. 3. Pp. 17. DOI: https://doi.org/10.1051/swsc/2013036
NASA (n.d.): Unkown. https://pwg.gsfc.nasa.gov/polar/telecons/archive/PR_E-PO/Aurora_flyer/aurora-flyer_p2.doc.pdf
NASA (2023): “What is an Aurora?”. https://spaceplace.nasa.gov/aurora/en/
NOAA (2024): “Aurora Tutorial”. https://www.swpc.noaa.gov/content/aurora-tutorial
