Unveiling the Northern Lights Mystery in Italy, November 2023

On the evening of November 5, 2023, at approximately 6:20 p.m., an exquisite spectacle of the Northern Lights graced the skies of Italy. But was it truly the Northern Lights that we witnessed? Let's unravel the story from the start.

The Solar Events of November 3, 2023

Two days prior, on November 3, the Sun experienced three eruptive events. These eruptions sent a flurry of charged solar plasma particles hurtling towards Earth. A combination of factors, including a unique magnetic field orientation and a coronal hole in the solar corona, allowed these particles to breach Earth's magnetic field and interact with our atmosphere. This interaction initiated a G3-type geomagnetic storm. Such eruptions are common and more potent when the Sun is at its peak activity, a cycle that repeats every 11 years.

The Birth of the Northern Lights

This solar event led to the formation of the Northern Lights, a result of the charged solar particles colliding with those in Earth's atmosphere. Post-collision, these particles emit radiation at wavelengths that produce the characteristic aurora colors. These solar particles, to penetrate our atmosphere, follow Earth's magnetic field lines, which converge at the poles. The auroras, therefore, predominantly form over the northern hemisphere, at an altitude of around 400 km. This elevation enabled even Italy to witness the upper red part of the aurora, courtesy of oxygen atoms.

The SAR Arcs Phenomenon

Simultaneously, another intriguing spectacle took place, the formation of SAR arcs. Despite the name, "Stable Red Auroral Arcs," these arcs are neither stable nor auroral. They differ from auroras in their formation, even though they are also triggered by charged solar particles.

Earth is enveloped by a system of ring currents, located between 10,000 and 60,000 km away, and are laden with millions of amperes carried continually by high-energy protons. During geomagnetic storms, these ring currents intensify due to an influx of low-energy protons. This surge results in the release of thermal energy into Earth's upper atmosphere, which we observe as SAR arcs. The energy released ionizes oxygen atoms in the upper ionosphere, emitting a red hue similar to the auroras' upper part.

Aurora or SAR?

Determining whether we witnessed an aurora or SAR is tricky. However, the PANOMAX webcam at Compaccio (Dolomites) captured the peak of the aurora borealis at 6:20 p.m. on November 5, 2023. The landscape was bathed in a red/pink glow, as evident in photo 1. It's worth noting that the webcam's view would have appeared more vibrant than what the naked eye could perceive.

So, what spectacle did the Italians capture in their photographs? It's likely that some captured one phenomenon, others the opposite, and a few perhaps both. For instance, Katiuscia Pederneschi captured an image (without any processing) around 6:15 p.m. from Senigallia (Marche, Italy) near the first auroral peak sighted over the Dolomites. This suggests that she might have captured the actual aurora borealis, but a SAR sighting can't be ruled out. Most images from central and southern Italy likely depict SARs.

The upshot?

Firstly, these celestial phenomena provided a visual treat, and since the Sun is yet to reach its activity peak in 2024, similar occurrences might still happen. Secondly, based on the time, location, and 'shape' of the phenomenon, one could try to discern whether the captured image is of a SAR or an aurora borealis.