Stunning Aurora Australis: May 2024’s Sky Phenomena Explained

Unveiling the Wonders of the 11-12 May 2024 Night Sky

The formation of auroras, including coronas (see below), is primarily caused by the interaction between charged particles from the solar wind and the Earth’s magnetic field. When these charged particles collide with molecules in the Earth’s atmosphere, they emit light of varying colors, creating the vibrant displays we see as auroras.

The solar wind, composed of charged particles emitted by the Sun, interacts with the Earth’s magnetosphere, which is the region around the Earth dominated by its magnetic field. This interaction causes the charged particles to follow the magnetic field lines towards the Earth’s poles. When these charged particles collide with molecules in the Earth’s atmosphere near the poles, they emit light. The colour dictated by the composition of the molecules encountered, e.g. oxygen:

• Green: This is the most common aurora color, occurring at altitudes of around 100-300 kilometers when oxygen atoms are excited and emit light at a wavelength of 557.7 nanometers.
• Red: This color can appear at higher altitudes (above 300 kilometers) when oxygen atoms emit light at a wavelength of 630.0 nanometers.

And then everything got very surprising! An auroral corona appeared directly overhead.

A corona occurs when the aurora borealis (in the Northern Hemisphere) or aurora australis (in the Southern Hemisphere) appears directly overhead or very close to it. This phenomenon is quite rare and considered the holy grail of aurora photography due to its breathtaking beauty and rarity.

So, while the solar wind does indeed interact with the Earth’s magnetosphere and follow magnetic field lines towards the poles, the auroras themselves occur at high altitudes above the Earth’s surface, and the converging rays are a result of the observer’s perspective from the ground.

A STEVE is a type of aurora that has some distinct characteristics compared to traditional auroras.

Key Characteristics of STEVE (Strong Thermal Emission Velocity Enhancement):

Appearance:

Color: STEVE typically appears as a narrow ribbon of light that is often pinkish-purple. It can sometimes have a green component, known as the “picket fence” structure, which appears as a series of vertical green stripes.

Shape: Unlike the diffuse, curtain-like appearance of typical auroras, STEVE manifests as a sharp, narrow arc that can stretch for hundreds of kilometers across the sky.

Formation:

STEVE is formed at lower latitudes than traditional auroras, which are usually found in the auroral zones near the poles.

It is associated with subauroral ion drift (SAID), a phenomenon where fast-moving streams of charged particles move through the Earth’s magnetosphere at subauroral latitudes.

To explain ‘lower latitudes’:

STEVE typically occurs at latitudes farther from the poles and closer to the mid-latitudes. For instance, while traditional auroras (aurora borealis and aurora australis) are most commonly observed at high latitudes (e.g., around 70 degrees north or south), STEVE can be observed at somewhat lower latitudes, closer to the equator than the typical auroral zones.

Cause:

The exact cause of STEVE is still under study, but it is believed to be related to unique interactions between the Earth’s magnetosphere and solar wind, specifically involving high-energy particles and strong electric fields in the subauroral zone.

Discovery and Study:

STEVE has been observed for many years by amateur aurora watchers, but it gained significant scientific attention in recent years, leading to its formal study and categorisation.

Citizen scientists, particularly members of the Alberta Aurora Chasers group, played a crucial role in drawing attention to this phenomenon, leading to increased scientific investigation.

Differentiation from Traditional Auroras:

Altitude: Traditional auroras typically occur at altitudes of about 100-300 km, whereas STEVE can appear at slightly lower altitudes.

Location: STEVE appears in regions further away from the magnetic poles compared to where typical auroras are seen.

Physical Mechanism: While traditional auroras are caused by the collision of solar wind particles with the Earth’s atmosphere, STEVE involves a different mechanism related to ion drifts and thermal emission enhancements.

And then another phenomena…

And in the same time frame of 30 minutes, pulsing started. The analogy was like clouds forming instantaneously then vanishing moments later having apparently moved quite a distance at speeds many times great than our terrestrial based winds. There was no consistency as to direction. Of course they were not clouds, but it’s the only way I can articulate the display. Occasionally I’d have a primal reaction and flinch/duck down.

(I attempted a movie of the pulsing, but sadly my camera could not gather in enough light)

Pulsating auroras, which are a variation of the more common steady auroral displays. They are characterised by rapid fluctuations in the brightness and intensity of the auroral curtains, often resembling pulsating waves of light moving across the sky.

These pulsations indeed can occur over very short time scales, sometimes within seconds, and can give the impression of clouds forming and dissipating rapidly. The movements can be quite dynamic and unpredictable, with changes in intensity and direction occurring suddenly and without a consistent pattern.

The primal reaction I experienced, flinching or ducking down, is apparently not uncommon among observers experiencing pulsating auroras for the first time. The rapid and unpredictable nature of the pulsations can evoke a visceral response, akin to instinctual reactions to sudden changes in the environment.

The exact mechanisms behind pulsating auroras are still not fully understood, but they are thought to be related to variations in the influx of charged particles from the solar wind and fluctuations in the Earth’s magnetosphere. These variations can lead to rapid changes in the energy levels of the auroral particles, resulting in the pulsating behavior observed.

Experiencing such a dynamic and awe-inspiring natural phenomenon is truly a rare and remarkable event. My description I’m told, captures the sense of wonder and primal awe that many people feel when witnessing the beauty and power of the auroras. It’s an experience to cherish and remember for a lifetime!

Southern Lights Aurora