Starting on May 11th, the strongest geomagnetic storm in 20 years occurred, directly impacting the increase in atmospheric density in low Earth orbit, exacerbating the decay rate of low Earth satellite orbits, and causing disturbances in the ionospheric electron density, affecting radio wave communication quality and navigation positioning accuracy.
However, the super geomagnetic storm also brought about stunning auroras.
On the evening of May 11th, in the Altay region of Xinjiang, China, and even in some parts of Beijing, magnificent auroras appeared.
At the same time, the International Space Station also released beautiful aurora photos taken in space. However, in comparison, auroras are usually green, but what China saw this time was red.
Why is that?
A stunning aurora borealis captured in Altay, Xinjiang. (From photographer's Weibo @Jeff's Starry Journey)
Actually, the aurora borealis is not just one color. When it occurs above 300 kilometers from the ground, it appears mainly in light red. At heights of 200-300 kilometers, it is predominantly deep red. Between 100-200 kilometers, it often appears green. Below 100 kilometers, it can be blue, purple, or a mix of various colors.
In polar regions, influenced by factors like the Earth's magnetic field, high-energy particles from solar activity can penetrate the atmosphere to about 100 kilometers above the ground.
In this region, particles collide frequently. Excited nitrogen molecules transfer energy to atomic oxygen through collisions, causing the emission of light with a wavelength of 557.7 nanometers, appearing as green.
In December last year, a green aurora was observed in the Mohe region of China, indirectly confirming the intensity of the geomagnetic storm at that time.
In general, in mid-latitude regions like northern China, the auroras occur in the high-altitude atmosphere around 250-400 kilometers above the ground, with a wavelength of 630 nanometers, appearing red.
However, the human eye is not very sensitive to this wavelength. Only when strong solar activity triggers intense geomagnetic storms and the red light is bright enough can we see the red auroras, like in these past few days.
