Conjure, in your thoughts’s eye, a visible to accompany the phrase ‘aurora’. What you think about could be dominated by the colour inexperienced, elaborate swirls and swooshes that dance throughout the sky above a frozen panorama.
But the opulent glows that seem within the sky – as atmospheric gasses are struck by energetic photo voltaic particles – aren’t restricted to probably the most well-known manifestation. Auroras can seem in a wide selection of hues that adjust in accordance with altitude, latitude, and which gasses are concerned.
For the notably highly effective geomagnetic storm that rattled Earth’s magnetic cage in May 2024, a wierd blue glow appeared. That will not be unheard-of… however this one was at low latitudes, reaching unusually excessive into the sky.
Now, utilizing photos snapped by citizen scientists in Japan, physicists Sota Nanjo of the Swedish Institute of Space Physics and Kazuo Shiokawa of Nagoya University have found out the almost certainly clarification for the eerie blue gentle.
But their clarification creates one other downside that atmospheric scientists might want to remedy.
“Our findings counsel that nitrogen molecular ions could have accelerated upward by some mechanism and have been liable for the formation of the blue-dominant aurora,” Shiokawa explains.
“To date, it’s not effectively understood how nitrogen molecular ions with giant molecular weight can exist at such excessive altitudes. Such ions should not simply capable of exist for lengthy intervals of time attributable to their heavy mass and quick dissociative-recombination time intervals; nonetheless, they’re noticed at excessive altitudes. The course of is shrouded in thriller.”
Earth’s auroras are normally the results of an enormous inflow of photo voltaic particles, unleashed from the Sun in a coronal mass ejection or photo voltaic wind. These particles stream by the Solar System.
If Earth is within the path of the eruption, the particles slam into the magnetic discipline, the place they’re diverted and accelerated alongside magnetic discipline traces to the poles, the place they’re dumped into the ambiance.
The interplay between the photo voltaic particles and the gasses in Earth’s ambiance causes the atmospheric particles to achieve a little bit of vitality. When the atoms making up the atmospheric gasses drop again to their authentic vitality state, the vitality is launched as a photon – that is the supply of the glow.
It’s just like the mechanism that makes fluorescent lights glow. And, as with fluorescent lights, the colour of the glow depends upon various factors, corresponding to the kind of particle, and the quantity of vitality they achieve and lose.
Green and purple auroras, for instance, are generated by oxygen atoms shedding vitality at completely different altitudes. Nitrogen atoms can emit blue and purple photons. When these hues combine within the sky, they will produce yellow, purple, pink, and orange colours.
Usually, low-latitude aurora is purple. But, on 11 May 2024, a pink glow lit up the sky at low latitudes, and a distinctly blue glow appeared shortly earlier than midnight. And we now have a robust new device for capturing auroral phenomena: the smartphones of fascinated aurora-watchers world wide.
With the wealth of photos and video collected on the blue aurora, the researchers have been capable of measure the phenomenon intimately.
They discovered that the aurora was organized in longitudinal buildings that ran alongside magnetic discipline traces, for round 1,200 kilometers (about 750 miles). It was additionally organized into three separate buildings, and reached excessive into the sky, between altitudes of 400 and 900 kilometers.
For context, the International Space Station orbits at a top of between 370 and 460 kilometers.
Currently, low-latitude auroras are considered associated to the ring present. This is a torus-shaped present of charged particles trapped inside Earth’s magnetosphere, circling the planet’s equator like a pool flotation ring.
A geomagnetic storm energizes the energetic impartial atoms (ENAs) within the ring, inflicting the low-latitude auroral glow.
But the researchers do not imagine that the ring present works for what they noticed.
“In this research, a construction of a number of hundred kilometers was discovered within the blue-dominant aurora within the longitudinal path, which is tough to interpret by ENA exercise solely,” Shiokawa says. “In addition, ENAs are unlikely to create auroral buildings aligned with magnetic discipline traces, as noticed on this research.”
It’s attainable the ring present performed a task, however the researchers imagine one thing else needed to have been at play to supply the distinct, field-aligned buildings noticed. They imagine that molecular nitrogen ions have been by some means accelerated upwards. But what accelerated them is unknown.
This means that there could also be some as-yet unidentified course of in Earth’s ambiance.
We could not have sufficient info on the present time to determine what that course of is. But solutions are tantalizingly inside grasp.
“As photo voltaic exercise will increase within the coming years,” the researchers write, “repeated case analyses of such blue-dominant auroras are anticipated to supply insights into the era processes of blue-dominant low-latitude auroras.”
The analysis has been revealed in Earth, Planets and Space.
