The origin of the Northern Lights is located on the Sun, which is 149 million kilometers from Earth. The appearance of a large group of sunspots is the first sign of intense coronal mass ejection activity. The energetic particles emitted by the Sun travel into space forming the solar wind.
This moves through interplanetary space with speeds typically between 400 and 800 km/s, dragging part of the solar magnetic field with it. The solar wind, interacting with the Earth's magnetic field also known as the magnetosphere, distorts it, creating a sort of magnetic bubble, similar in shape to a comet.
Earth's magnetosphere works like a shield, shielding the Earth from the direct impact of the charged particles that make up the solar wind. To a first approximation these particles slide along the outer edge of the magnetosphere and pass beyond the Earth.
In reality, due to a process known as magnetic reconnection, the plasma of the solar wind can penetrate into the magnetosphere and, after complex acceleration processes, interact with the Earth's ionosphere, depositing immense quantities of protons and electrons in the upper atmosphere, and thus giving rise to the phenomenon of auroras.
It should be noted that the Arctic areas, having less magnetic protection, are the most exposed to this phenomenon and often, for a few days after the event, ozone is reduced by around five percent.
The magic of the Northern Lights
Auroras are most intense when there are magnetic storms caused by strong sunspot activity.
The intensity distribution of auroras at altitude shows that they predominantly form at an altitude of 100 km above the Earth's surface. They are typically visible in regions near the poles, but can occasionally be seen much further away, up to 40° latitude.
Particles moving towards Earth hit the atmosphere around the poles, forming a kind of ring, called the auroral oval. This ring is centered on the magnetic pole and has a diameter of 3,000 km in quiet periods, growing when the magnetosphere is disturbed.
Auroral ovals are generally found between 60° and 70° north and south latitude. The aurora is formed by the interaction of high-energy particles, typically protons and electrons, with neutral atoms in Earth's upper atmosphere.
These particles can excite, through collisions, the valence electrons of the neutral atom. After a characteristic time interval, these electrons return to their initial state, emitting photons. This process is similar to the plasma discharge of a neon lamp.