Voices from the Sky

by | 27 Apr, 2023 | Astronomy, Nature, Photography, Weather | 0 comments

(The title of this piece has been borrowed from Arthur C. Clarke.)

Writing when sleep deprived is not the best of ideas, but I’m fired up from the events of last night (23rd-24th April, 2023). All the reports suggested an intense CME (coronal mass ejection – a large cloud of magnetised plasma from the outermost surface of the Sun’s atmosphere) was heading our way. Before darkness had even set in, the atmospheric disturbance level on my AuroraWatch UK app shot up to 919.9nT (nT=nanotelsa – a unit of measurement for magnetic field strength.) To put that in context, the last time I saw the aurora borealis from Devon (exactly a month ago, from the 23rd-24th March) the disturbance level only went up to 236nT. 

I went out before it was really dark, up in the field behind our house. To the west, the waxing crescent Moon, lit with earthshine, hung close to Venus in the constellation of Taurus. Mars was positioned above the red supergiant Betelgeuse in Orion the Hunter, his belt pointing towards Sirius, a star like a disco ball which is sometimes mistaken for a UFO.

At 9.30pm, when the residues of daylight were still evident in the sky, I noticed fast-moving patches of white above my head. Initially, I wondered if they were clouds, but the speed they were moving and the direction of their travel (north to south) made me wonder if they were a form of diffuse aurora. Pointing my camera directly upwards, I realised that they were aurora; what my eyes were seeing as faint white patches were in fact green spots of it drifting across the sky. I also realised that an auroral arc was directly over my head, stretching into the south west – which is quite a thing when you consider I live in Devon, at 50º N.

Aurora borealis in Devon UK.

The arc, which I couldn’t see with my eyes but was easily recognisable via my camera, remained in the sky for the next hour. It was like a cerise river, its western end cascading between Orion’s shoulders and the eastern end somewhere off in the east, behind the trees. 

Auroral arc, 23rd April 2023, from Devon, UK.

Meanwhile, in the north, there was a near constant, faint haze of aurora, but it was struggling to compete with light pollution from the town of Chard. A Barn Owl called somewhere off across the fields, an otherworldly wail that would have made my hairs stand on end if I didn’t know it well. 

I caught the tail end of a Lyrid meteor, its bright flash leaving a trail of smoke in the sky. Foxes squabbled and for a while, everything stayed largely the same. The arc continued to float above me and the Moon and Venus descended.

Then, just before 11pm, I heard a sound I have never heard before. It came from the sky just behind me, lasting no more than a handful of seconds. It sounded like something vibrating, something akin to a large insect’s wings, a flag in a gale and the aftershock from a distant bolt of lightning. Nothing around me changed; there was no wind or any flash. But I knew something had happened. Something different and unknown. I turned, scanning the Oak trees behind me for some form of discernible movement. They stood still as statues. It was too cold for insects and, having carried out a number of bat surveys, I knew the sound did not come from a bat’s wings. Did the vibrating noise have something to do with the geomagnetic activity in the atmosphere? 

Aurora borealis 23rd April 2023, from Devon, UK.

A few seconds to a minute later, the aurora to the north began to dance. Tall rays of light rippled through the sky, rays that I could easily see without my camera, although to my eyes they weren’t brightly coloured. With my camera, they appeared as cherry red curtains which danced and weaved over the horizon, stretching westwards towards Earth’s two closest neighbours as they set behind the trees.

Aurora borealis from Devon, UK. 23rd April. 2023. Photograph by Kerrie Ann Gardner.

For a long time, scientists have remained sceptical of auroral sounds. This is because aurorae averagely occur around 100km above the Earth, which is too high for any discernible sound to reach an observer at ground level. British physicist Sir Oliver Lodge suggested that the sound might be a psychological phenomenon, a synesthetic illusion caused by the vividness of the lights. But that doesn’t match my experience, as I heard the sound before what I took to be the brightest part of the display. 

Aurora borealis from Devon, UK. 23rd April. 2023. Photograph by Kerrie Ann Gardner.

In 1885, Sophus Tromholt, who was considered an outsider in the Scandinavian scientific society of the time, sent out several thousand letters to residents in Norway asking if they or their acquaintances had heard the aurora. His interest in the phenomenon was likely encouraged by his father, who claimed to have heard auroral sounds on three separate occasions in 1838, 1840 and 1843, likening them to the sound produced by rubbing two pieces of paper together at speed. 

Tromholt received 114 responses from residents in Norway. 92 of the respondents expressed a belief in auroral acoustics, with 53 of them claiming to have heard the sounds themselves and 39 reporting they had acquaintances who had. 21 people reported that they had never heard any sounds when there was auroral activity and 31 did not express a view either way. 

Descriptions of the sounds heard by the residents included such things as: ‘tearing silk’, ‘burning dried juniper’ and ‘the buzzing of a bee’. The similarity of the descriptions gave Tromholt’s survey some credibility, but being anecdotal, there was still much scepticism from the scientific community. British spectroscopist and amateur astronomer John Rand Capron conducted a similar survey in 1879 with residents from the north of the UK, but he determined the results were: ‘quite adverse to any proof of noises proper ordinarily accompanying aurora’ – perhaps because, despite his efforts, he never heard the sounds himself. 

And yet, reports of audible aurora have been accumulating for many years. My experience was galvanised when I found the earliest reference of auroral acoustics, reported by Samuel Hearne in the 1700s. Long before Tromholt and Capron’s surveys, Hearne claimed to have heard a: ‘rustling and crackling noise like the flapping of a large flag in a gale of wind’ during auroral activity in Canada – a description uncannily similar to the analogy I used. 

David Thompson, who spent the winter of 1796-1798 at Reindeer Lake, Saskatchewan, reported that he and his men saw and heard brilliant aurora: ‘In the rapid motions of the Aurora, we were all persuaded that we heard them, reason told me that I did not but it was cool reason against sense.’ But he struggled to accept the idea and decided, after blindfolding his men and asking if they were still able to hear the lights, that the sound was psychological – even though the blindfolded men continued to report sounds. Another man who used the blindfold technique to assess if there was any sound associated with aurorae was William Ogilvie, who blindfolded one particularly adamant member of his party in 1882 during auroral activity and carefully observed his reactions. At: ‘nearly every brilliant rush of the auroral light’ the blindfolded man exclaimed: “Don’t you hear it?” But Ogilvie was unaware of any noise. 

The numerous testimonials of people claiming to have heard the aurora (with indigenous groups reporting them as a matter of course) are remarkably similar. Published in The Journal of the Astronomical Society of Canada in 1923, is a collection of testimonials collated by C. A. Chant. Soon after, C. S. Beals sent circular letters to people who had lived or travelled in Canada, asking if they had ever heard any sound accompanying the aurora and, if so, what was the nature of the sound. (In the same study, he also collected eye witness accounts of auroral streamers which approached the surface of the Earth.) His results make for convincing reading – 144 respondents reported hearing audible sounds, with 95% of them using words such as ‘hissing’, ‘swishing’ and ‘rustling’ to describe them. 

But, without any concrete evidence, this data is easily criticised, as there was still: ‘no widely accepted physical model or reasons for the sounds.’ An attempt to remedy this took place at the Geophysical Institute of Alaska from 1962-1964, with The Investigation of Auroral Sound Waves project, which used two condenser microphones about 12 miles apart to monitor vertical sound waves. Unfortunately, the project did not yield a single recording for scientific publication. The team concluded that the timing of their study (which was carried out during solar minimum) was the reason for the negative results. 

Finally, in 1999, Professor Unto K. Laine, from the former Helsinki University of Technology (HUT), approached researchers at Sodankylä Geophysical Observatory (SGO), asking if they would like to join forces to study acoustical phenomena related to the northern lights. In February 2000, Laine visited Sodankylä, where PhD Esa Turunen and PhD Jyrki Manninen agreed to start a cooperation focusing on the sounds. A questionnaire web page was opened to collect observations of auroral acoustics in Finland, and the project was introduced to newspapers and some radio programmes. Later, the Finnish Meteorological Institute (FMI)  joined the project, which was titled Auroral Acoustics.

From the 6th-7th April, 2000, during a solar storm, the first attempt at recording auroral sounds was carried out by Laine in southern Finland. Between recordings, Laine reported hearing a: ‘quite constant noise from the sky when blood red auroral curtains were hanging from the zenith.’ The noise was even clear enough to mask other environmental sounds. A week later, a recording was made with the same instruments under similar weather conditions. A comparison of the two recordings revealed an increased level of noise during the night of the solar storm, including sound ‘claps’. However, as the first recording was completed with a low quality system, the resulting recordings had technical problems which made analysis difficult. After this, a new method was developed. New recordings were almost always collected when the weather conditions were favourable and higher geomagnetic activity was predicted. The majority of these recordings were collected by Laine in southern Finland, with some by the SGO at Sodankylä.

During a solar storm which took place from the 11th-12th April, 2001, recordings were made at Koli, Finland, allowing Janne Hautsalo, a member of Laine’s team, to produce an excellent Master’s thesis with detailed statistical analyses of the Koli recordings. The thesis showed statistically significant connections between the recorded sounds and geomagnetic activity measured simultaneously by the FMI.

However, even though the project amassed close to 300 auroral sound reports, collected 50 auroral recordings, published the results at international conferences and proved a relationship between geomagnetic activity and auroral sounds, a lack of funding forced Auroral Acoustics to suspend. Regardless of the evidence collected, the long held belief in the Finnish field of geophysics was that the aurora was incapable of producing sounds, and any sounds heard must therefore be a figment of the observer’s imagination. Consequently, all funding applications outside the participating institutions were rejected.

This scepticism forced Laine to continue working on the project alone. But, with limited funding and only one microphone, it was impossible to localise the sound source, leaving the project at a methodological dead end. Therefore, from 2005-2011, Laine concentrated on research in other fields of acoustics. In 2010, he was appointed Professor of Acoustics at Helsinki University of Technology (HUT).

During this time, Laine continued to study historical documents related to auroral sounds and collected more observational reports. He also developed analysis methods and looked into new mathematical ways to predict solar activity. Then, in 2010, the Finnish Journal Tiede asked Laine to write an article on auroral sounds. After this, Laine began to make plans to start the next phase of the Auroral Acoustics project. A new focus was decided: localisation of sound sources, as without this data, there was little hope of solving the physics behind the sounds.

The second phase of the project started in summer 2011, by constructing a new VHL loop antenna. It was made to fit the XLR connector of a sensitive microphone preamplifier. Two new microphones and a four-channel recorder were acquired. From 11th-12th September, 2011, a recording was made near the village of Fiskars in Finland. Analysis of the recorded material revealed 20 ‘clap’ sounds, allowing an estimation of the sound source. It came as quite a surprise – the sounds had come from an area approximately 70m above the ground in the open sky. The results were published but, as it was still unknown, there was no accompanying explanation for what generated the sounds.

From March the 17th -18th, 2013, recordings made at the village of Fiskars during a strong geomagnetic storm showed around 70 impulsive sound events. Their source was estimated to be about 75m above the ground in the open sky. This lead Laine to his Inversion hypothesis:

A temperature inversion layer forms an isolating lid at an altitude of 60-400 metres. Warm air with aerosols rises up and carries negative charges to the lower part of the inversion layer. A geomagnetic storm increases the conductivity of the upper atmosphere. Positive charges are accumulated above the inversion layer. The electric potential over the inversion layer is increasing similarly to a capacitor during charging. Finally, a sudden discharge occurs that produces a crackling or clapping sound together with magnetic pulses. 

It has also been surmised that the inversion hypothesis might explain why some observers have reported hearing meteors. 

Although the Auroral Acoustics project still has a number of unanswered questions – mainly that it hasn’t yet discovered why the discharging mechanism is triggered –  it has improved our understanding of the ‘auroral theatre’ and given credence to hundreds of people’s testimonials. Some scientists are still sceptical, but during the Fiskars village experiment Laine was able to prove, via a weather balloon and a short duration test sound from the ground, that the estimated distance of the auroral sound and the inversion layer were at the same height, signifying that there is a relationship between the two.  

Often associated with high pressure, a temperature inversion forms under still conditions. Air that is higher in the troposphere sinks towards the ground, drying and warming as it falls. It then acts as a lid, tapping cooler air near the Earth’s surface. This is why it is called an inversion, as the usual pattern of things has been reversed. If you were to climb a mountain in such conditions, you would meet warm air instead of cold. Although they happen all year round, temperature inversions are more common on clear nights during the winter months, trapping mist and fog close to ground level. 

Unbeknown to me at the time, the conditions from my location on the night of the 23rd-24th April were auspicious not just for viewing the aurora, but for hearing it as well. After a largely cloudy day, the sky cleared, and mist began to form near the ground. There was little to no wind (I recall one single gust) and as the night went on, the temperature dropped. There is a tendency for mist to form near our house, encouraged, I presume, by its low topographical situation (it sits in a dip in the landscape) allowing cold air to settle and condense. Sometimes, when I’ve cycled home after dark, I can feel the temperature drop as I reach our drive. It’s a bit like cycling into a fridge. 

Aurora borealis from Devon, UK. 23rd April. 2023. Photograph by Kerrie Ann Gardner.

I know there will be people who are sceptical of my experience. I’m aware that it puts me into a certain bracket of the population, alongside those who have seen or heard other uncommon phenomenon, like ball lightning or Will-o’-the-Wisp. However, just because auroral acoustics are not a regular occurrence, it does not mean that they do not exist. And I can think of nothing else that could have made the sound I heard. 

Aurora borealis on the 23rd April 2023, from Devon, UK. Photograph by Kerrie Ann Gardner

The CME which hit the Earth’s magnetic field from the 23rd-24th April, 2023 sparked a G4-class geomagnetic storm, otherwise known as ‘severe’. Aurorae were seen as far south (or north) as China, Kazakhstan, Western Australia, Southern Spain, Texas, New Mexico, California, Arizona and Florida. It was a big event and, as such, was surely capable of creating significant levels of positive charge in the Earth’s atmosphere above a temperature inversion. Although the trigger for discharge is still unknown, I wholeheartedly believe that the Auroral Acoustics project has found an answer to the enigma of auroral sound and I will always argue that, as improbable as it might seem, I heard a discharge in the area of sky above me while standing in a field in Devon, at 50ºN. A murmur of static charge high above my head – otherwise known as voices from the sky.

P.S. After publishing this blog, I contacted Professor Unto K. Laine to let him know of my experience, as I thought he might be interested to know that someone at 50º N had heard the aurora (he was). Since then, he has been a great source of information and I am very grateful for his time and generosity; much of this blog, which I have edited since its first publication, would not exist without him. It should also be mentioned that his own interest in auroral acoustics was sparked after hearing the sounds with a group of friends in Lapland in 1990. Afterwards, he discovered that the concept of auroral sounds has been subjected to a lot of debate over the years – debate which wrongly marginalised the experiences of native people. Many scientists, certain of the improbability of the sounds, were unwilling to study the phenomena, replacing scientific study with speculation. Laine, who has suffered a fair amount of ridicule himself for his work on the subject, told me that his two biggest motivations for the Auroral Acoustics project were ethics: ‘think of all the talented people who made correct and valid observations but were ridiculed’ and curiosity: ‘the possibility to discover something new’. That, it seems to me, is the mark of a true scientist. As Jukka Ruukki, editor-in-chief of Tiede wrote in his editorial:

Wild ideators and dissidents push science forward. If all the progress in the world had been in the hands of realists, we would still be sitting in trees and mumbling bananas.


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