Exploring the mysteries of rare phenomenon in the night sky: SAPS, SAID, STEVE, SAR, IPA and pulsating aurora

There’s something deeply magical about witnessing the phenomena of the night sky. The cosmic energy above our heads constantly offers glimpses of beauty and mystery, pulling us into a sense of awe and wonder. Recently, I found myself immersed in a particularly extraordinary event, observing pulsing green blobs of light, a phenomenon tied to proton auroras, rather than the more commonly observed electron triggered aurora. They were being witnessed across the UK and a few fellow aurora chasers and I were chatting about everything we were witnessing from different parts of the country, just showing the sheer scale of the night sky. This experience has only deepened my fascination with the rarer phenomena of the night sky, including SAID, STEVE, SAR, IPA and pulsating aurora. Understanding more about these phenomena has made me want to revisit my entire aurora collection since 2014, to see if I captured any of them before my awareness of them started!

In this post, I’ll walk through each of the phenomenon I’ve observed and aim to demystify the rare wonders of the night sky.

As a side note and reminder, as a citizen scientist and pro photographer that has been chasing the aurora since 2014, I am always thrilled to contribute my observations to further our understanding. Please contact me directly hello@rebeccadouglas.co.uk if you wish to use my Images to discuss usage and permissions.

Ok, with that reminder, well, reminded – let’s dive in!

Aurora borealis

As a benchmark, I wanted to share a reminder of how the aurora borealis forms, so each of the rarer phenomena can be understood. Aurora is a visible manifestation of Earth’s atmosphere, as it literally allows us to see something that without it is usually invisible! The Northern Lights are caused by the interaction between charged particles from the solar wind and plasma when it hits Earth’s upper atmosphere. During periods of increased solar activity, solar particles (mainly electrons) excite gases in our atmosphere and the gases move to a higher energy state. When they return to their lower energy levels, they release photons, particles of light. This is what we see from the ground as aurora. Below you can see all of the colours of the aurora borealis, as the corona explodes overhead.

SAR – Stable Auroral Red Arc

I’ve witnessed these mesmerising red arcs banding across the sky at least a couple of times, but they were first witnessed in 1956! The first I’ve knowingly seen was on the 5th Nov 2023 display in the UK, where one glowed overhead for hours, with aurora chasers in Eastern Europe and the North America/Canada area all witnessing it at the same time! These phenomena are known as Stable Auroral Red Arcs (SAR) and can be easily mistaken for aurora because they are equally as captivating celestial displays. Unlike traditional auroras that shimmer in greens, reds and purples with solar energy exciting gases in the magnetosphere, a SAR events appear as a steady, reddish glow across the sky due to oxygen in the ionosphere being. “Stable auroral red (SAR) arcs are the consequence of interaction of the outer plasmasphere (plasmapause) with energetic ions of the ring current.” (I.B. Ievenko, 2020) And as J. Baumgardner et al, 2007 state ” The SAR arc emission at 6300 Å is driven by field-aligned magnetospheric energy transport from ring current/plasmapause locations into the ionosphere-thermosphere system.” They form equatorial side of the main auroral arc and are often more subtle, blending quietly into the sky rather than dazzling with rapid, vibrant movements that are characteristic of the main auroral arcs.

SARs are tied to the inner workings of the Earth’s atmosphere and how it interacts with solar energy and they often appear during intense geomagnetic storms. There’s something haunting about their slow, crimson hue, as if the sky itself is holding its breath, gently radiating the energy stored during periods of magnetic disturbance. SAR reminds us that not all cosmic phenomena need to be flashy to command attention; sometimes it’s the quieter movements that leave a lasting impression.

In summary, a Stable Auroral Red arc (SAR) is :

• What it is: SAR is a very stable and faint red arc of light that can appear during intense geomagnetic storms, located at higher altitudes of our atmosphere than typical auroras.
• Cause: It is related to the heating of gases in the Earth’s atmosphere and SAR arcs appear when energy from the magnetosphere transfers into the ionosphere, Earth’s upper most atmosphere.
• Location: SAR is usually located equator-ward of the auroral oval (closer to mid-latitudes), and it remains relatively stationary and can be present for hours, stretching across continents.
• Distinct Features: Unlike typical auroras that can vary in brightness and shape, SAR arcs are much more stable, appearing as faint and continuous arcs of red light. Their appearance is usually faint, making them difficult to see with the naked eye, but on nights of intense activity their colour can become more vivid.

Isolated Proton aurora (IPA) – Earth’s rings in motion

Isolated Proton Auroras (IPAs) are a sight to behold, linked to massive geomagnetic storms, when charged particles (protons) from the sun rain down into the Earth’s magnetosphere. While most auroras are caused by electrons, proton auroras arise from the interaction of energetic protons. During the night of 10th October 2024, I had the chance to witness this rare phenomenon at Elmley Nature Reserve. Just after midnight, the sky pulsed with green blobs of light, as if the very fabric of the night was alive and breathing. These glowing, pulsing patches were not your typical auroral curtain; they seemed to pulse with energy and come and go, which made them all the more curious to observe.

This incredible research paper outlines a discovery that revealed these IPAs have an impact on our atmosphere, in quite a dramatic way! ‘For the first time, the data revealed the formation of a localised ozone hole in the mesosphere, about 400 km wide, which was associated with isolated proton auroras. While decreased ozone was observed, this phenomenon should have no effect on the stratospheric ozone layer that protects life on Earth.  

Comparing their results to simulations, the researchers found that the change was much greater than predicted. Up to 10-60% of the ozone directly below the aurora was destroyed 90 minutes after it began. However, the researchers stress that this change is expected to heal naturally and cause no long-term decline in the ozone in the mesosphere.’ Source: Eureka Alert.

It was during the strongest part of the storm that these eerie blobs appeared. The sheer power of the storm made the air electric, as if the sky was alive with an invisible current. Proton auroras are rare and often appear in unusual shapes or movements compared to regular auroras, but this night was something out of the ordinary, a true moment of connection between Earth and the cosmos, one that left me spellbound. It is always so exciting to make discoveries about the night sky like this!

In summary, an Isolated Proton Aurora (IPA) is:

• What it is: Isolated Proton Auroras are a type of auroral phenomenon that appears as diffuse, faint patches or arcs of light, typically in a greenish hue.
• Cause: Unlike traditional auroras caused by electrons, Isolated Proton Auroras result from the precipitation of protons into Earth’s upper atmosphere during geomagnetic storms. These protons interact with the atmosphere, releasing energy that causes the characteristic glow, often at higher altitudes than electron-driven auroras.
• Location: Proton auroras are typically found equatorial side of the main auroral oval but can extend to lower latitudes during intense geomagnetic storms.
• Distinct Features: Proton auroras are usually less vibrant and less structured than electron-driven auroras, often appearing as diffuse, featureless glows. They lack the swirling or curtain-like shapes of traditional auroras and are more often pulses or blobs of light.

Subauroral Polarisation Streams – SAPS

The term Subauroral Polarisation Streams (SAPS) was first introduced and defined in a paper by Foster et al. (2002) as an inclusive, unifying term to describe the intense westward plasma flows observed equatorward of the auroral oval during geomagnetic activity. They state ‘subauroral electric fields play critical roles in energising and transporting ring current ions, as well as convecting thermal plasma in the inner magnetosphere and in the mid- to low-latitude ionosphere.

While SAPS itself is not a visible phenomenon, the detection of SAPS can coincide with the appearance of SARs, STEVE and in some cases, isolated proton aurora (IPA), although it is important to note these have different formation mechanisms, they share the same spatial region, the equitorial side of the main auroral arc and may be triggered by the same geomagnetic conditions.

Subauroral Ion Drifts – SAIDs

Subaurora ion drifts, (SAIDs) are not visible to eye or camera, only something that is detected by instruments. “Subauroral ion drifts (SAID) are latitudinally narrow regions of rapid westward ion drift located in the evening sector and centred on the equatorward edge of the diffuse aurora”. Anderson et al. 1991.

What makes SAID particularly fascinating is its role in the subauroral region during geomagnetic disturbances. These flows can coincide with other rare phenomena, and it is possible that STEVE is the visual manifestation of SAID. The understanding is evolving to understand how they play a part in the complex chain of events that unfolds during solar storms. Research undertaken by MacDonald et al in (2018) that analysed one STEVE event was then extended by Archer et al. (2019). They considered 8 occasions where both STEVE and SAID had been observed to determine if STEVE is the optical signature of subauroral ion drifts (SAIDs). They compared European Space Agency’s Swarm satellites data that detected a SAID with occurrences of STEVE and found them to occur at the same time, concluding ‘regardless of the specific mechanisms responsible for Steve, the observations presented in this study suggest Steve to be the optical signature of exceptionally intense SAID.’

In summary, SAID is:

• What it is: SAID refers to a narrow region of extremely fast-moving ions (charged particles) in the Earth’s ionospere, located just equatorward of the auroral arc.
• Cause: SAID is a result of geomagnetic storms and disturbances in the Earth’s atmosphere, which drive fast moving ions in the sub-auroral region.
• Location: This phenomenon occurs in the sub-auroral region, just equatorward of where typical auroras form.
• Distinct Features: SAID is a plasma (charged particle) phenomenon, not a visible light display. It’s detected using scientific instruments rather than being observed visually like auroras or STEVE.

STEVE – Strong Thermal Emission Velocity Enhancement

STEVE might sound like a quirky name for a cosmic event, but this phenomenon is anything but ordinary. STEVE, a Strong Thermal Emission Velocity Enhancement, was once mistaken for an aurora, but scientists have discovered it’s a unique atmospheric event that glows as a thin, purple arc, often accompanied by “picket-fence” green streaks. What makes STEVE so enchanting is its elusive nature; it doesn’t appear during typical auroral displays but instead during specific geomagnetic conditions.

This band of light stretches for hundreds of kilometers, separate to the main auroral arc making it stand out starkly against the darker sky. Witnessing STEVE is like seeing a ribbon of cosmic energy, and in the northern hemisphere it is south of the active aurora arc. Its appearance is a rare but unforgettable sight, serving as a reminder of just how many untold secrets the night sky still holds.

In summary, STEVE is:

• What it is: STEVE is a curious phenomenon that occurs on nights of strong geomagnetic activity, but it is distinctly different from regular aurora. It appears as a narrow, purplish-pink or white band of light, sometimes accompanied by “picket-fence” green structures, separate to the main arc of aurora.
• Cause: It is believed to be caused by a high-speed flow of charged particles in the ionosphere, though not as a result of the same mechanisms that produce the traditional auroras. It is thought that STEVE could be the optical signature of subauroral ion drifts – discussed in the next section.
• Location: STEVE usually occurs at lower latitudes than the main auroral arc, often first seen in the west of the sky.
• Distinct Features: It doesn’t have the typical swirling and curtain-like structures of auroras, often appearing in a completely separate part of the night sky. The purplish or white hue can glow intensely, with a very defined structure.

Witnessing SAID, STEVE, SAR & IPA unfold – Geomagnetic Storm – 5th November 2023

On 5 November 2023, Thanet skies lit up with an extraordinary display of auroral and subauroral phenomena, including the rare appearance of STEVE, SAR arc and IPA. While STEVE, SAR and IPA are not electron triggered aurora in the traditional sense, as we’ve seen in this post, they’re part of the incredible complex events triggered by space weather during powerful geomagnetic storms. In this video you can see everything sequence together and it was utterly remarkable to witness this first hand!

Dive into this night of aurora and surreal phenomenon over in this post, by clicking here.

Pulsating aurora: A rare celestial dance

Pulsating auroras are a rare and fascinating form of auroral display that differ from the more familiar sweeping curtains of green and purple light. These auroras appear as flickering, irregular patches that pulse in and out, creating a mesmerising effect in the night sky. Unlike typical auroras, which are powered by continuous solar wind energy, pulsating auroras are driven by intermittent plasma waves called ‘whistling mode chorus’ (Source, NASA). These waves scatter their electrons and cascade down our atmosphere, exciting oxygen and they release light as they slow down and create the pulsing aurora. They typically occur at the end of a geomagnetic storm and to the eye they are more subdued than traditional auroras, making them a subtle but captivating phenomenon. I often call them ‘aurora soup’ because the sky is full of aurora but it lacks much definition and so the sky feels a bit like how we describe fog as a ‘pea soup-er’ in the UK.

In summary, pulsating aurora is:

• What it is: Pulsating auroras are faint, flickering patches of light in the night sky that pulse in and out, unlike the more continuous, flowing auroras.
• Cause: They are caused by the interaction of charged particles from the solar wind with Earth’s magnetosphere, leading to scattered electrons entering the atmosphere and exciting oxygen atoms, which release light as they slow down.
• Location: Pulsating auroras typically occur at lower latitudes than traditional auroras and are often seen after the main phase of a geomagnetic storm.
• Distinct Features: Unlike standard auroras, which tend to follow the pattern of building in intensity, dancing/glowing arc with pillars and then they fade, pulsating auroras appear in irregular, patchy areas of the sky, with the light pulsing on and off in a rhythm. They are less vivid and more subtle, often flickering in the sky for hours.

Summary:

• SAPS: Subauroral Polarisation Streams – intense westward plasma flows observed equatorward of the auroral arc during geomagnetic activity.
• SAR: Stable auroral red arc are the consequence of interaction of the outer plasmasphere with energetic ions of the ring current.
• SAID: Subauroral Ion Drift – a fast-moving stream of charged particles in the sub-auroral region, not visible but detected with instruments, occurring during geomagnetic disturbances.
• STEVE: Strong Thermal Emission Velocity Enhancement – a visible band of light with a white and purplish-pink colour, distinct from typical auroras, caused by high-speed particle flows in the ionosphere. May be a optical signature of a SAID.
• IPA: Isolated Proton Auroras – diffuse, faint green patches, blobs or arcs of light caused by the precipitation of energetic protons during geomagnetic storms, typically less structured and vibrant than traditional auroras.
• Pulsating Aurora: Irregular, flickering patches of light that pulse on and off in the night sky, caused ‘whistling mode chorus’. These waves scatter their electrons and cascade down our atmosphere following geomagnetic storms. They are subtler and less vivid than traditional auroras, appearing as rhythmic, patchy glows.

A cosmic invitation

These night-sky phenomena SAPS, SAID, STEVE, SAR, IPAs and pulsating auroras remind us how much of the cosmos remains a beautiful mystery. They invite us to look up and reconnect with the celestial rhythms that often go unnoticed in the rush of daily life. Each display is unique, a dance of light and energy that bridges the gap between our world and the infinite beyond. Whether it’s the invisible currents of SAID, the elusive purple glow of STEVE, the subtle red hues of SAR, the rare and eerie green glowing blobs of isolated proton auroras or the pulsating flickering aurora caused by whistling mode waves, the night sky is always offering a window into the extraordinary.

What blows my mind, is that all of this is caused by energy that left the surface of our sun and our atmosphere gets activated by all of this geomagnetic energy, triggering these reactions in the gases and all of these incredible sights appear!

So, the next time you find yourself under the stars, take a moment to breathe it in. You never know what rare phenomenon might be waiting just above the horizon, ready to reignite your curiosity and remind you of the magick woven into the fabric of our universe.