Aurora Service Radio
Our planet is a natural source of radio waves at very low audio frequencies. You could call the Earth a natural radio station. This natural radio station has been running for millions of years, but it’s only quite recently humans have been able to tune into it. So we have done exactly that. We have built a VLF (very low frequency) radio receiver at Aurora Service HQ (60°N Finland) to listen to the sounds of Earth and it’s ionosphere/magnetosphere, which we are broadcasting live right here so you can tune in any time 24/7. During times of high geomagnetic activity you can actually hear the Northern Lights (even if it’s cloudy or the skies are too bright!). Therefore, the best time to tune in is night time. You can hear lightning striking the planet almost 24/7.
The very low frequency range is highly susceptible to interference, mostly from AC electricity from houses and from powerlines. We have eliminated as much as we could as we have sited the antenna (which is in fact a Birch tree) about 80 metres from the building, but there is still a little AC hum in the background for which we apologise. Any VLF pro’s please get in touch with any ideas and/or software filters.
Click here for lots of details and pics on how we built the system.
Listen Live now:
The Radio service is temporarily down due to stormy weather last week a few things got damaged, it should be back up very soon.
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What is VLF (very low frequency radio)?
If humans had radio antennas instead of ears, we would hear a remarkable symphony of strange noises coming from our own planet. Scientists call them “tweeks,” “whistlers” and “sferics”. They sound like background music from a flamboyant science fiction film, but this is not science fiction. Earth’s natural radio emissions are real and, although we’re mostly unaware of them, they are around us all the time.
“Everyone’s terrestrial environment almost literally sings with radio waves at audio frequencies,” says Dennis Gallagher, a space physicist at the Marshall Space Flight Center (MSFC). “Our ears can’t detect radio waves directly, but we can convert them to sound waves with the aid of a very low frequency (VLF) radio receiver.”
The source of most VLF emissions on Earth is lightning. Lightning strokes emit a broadband pulse of radio waves, just as they unleash a visible flash of light. VLF signals from nearby lightning, heard through the loudspeaker of a radio, sound like bacon frying on a griddle or the crackling of a hot campfire. Space scientists call these sounds “sferics,” short for atmospherics.
Even if there is no lighting in your area, you can still hear VLF crackles from storms thousands of kilometres away. Some sferics travel all the way around the Earth! Radio waves can propagate such great distances by bouncing back and forth between our planet’s surface and the ionosphere – a layer of the atmosphere ionized by solar ultraviolet radiation. The ionosphere, which begins about 90 km above the ground and extends to thousands of kilometres in altitude, makes a good over-the-horizon reflector of low frequency radio waves.
“The ionosphere and the surface of the Earth form a natural waveguide for VLF signals,” explains Bill Taylor, a space scientist at the Goddard Space Flight Center. Sferics that travel very far through the waveguide become “tweeks,” which produce a musical ricochet sound in a VLF receiver. Tweeks sound as they do because their high frequency components reach the receiver before their low frequencies do.
Sometimes the ionosphere leaks lightning pulses into space. They exit Earths atmosphere entirely, following magnetic field lines that guide them 10,000 km or more above Earth’s surface, into our planet’s magnetosphere and then back again.
“Lightning pulses that travel all the way to the magnetosphere and back are highly dispersed, much more so than tweeks,” continued Gallagher. “We call them ‘whistlers’ because they sound like slowly descending tones. Whistlers are dispersed, not because of the waveguide cutoff effect, but rather because they travel great distances through magnetized plasmas (a plasma is an ionized gas), which are strongly dispersive media for VLF signals.”
Natural VLF Radio Sound Descriptions
What you will hear on the live stream above will vary depending on time of day and aurora/geomagnetic activity.
Lightning-stroke “static“: If your already listening to the live stream, you may be hearing (or may even be fed-up with) the nearly constant crackling and popping noises. An unavoidable part of Natural VLF Radio, lightning static is ALWAYS audible, though, depending on the location and time of year, the amount of lightning static can widely vary.
Generally, recordings made in summer are plagued with lightning storm static and those made in mid-winter tend to be wonderfully quiet. While a nuisance to some listeners, VLF lightning static is trying to tell us something. Imagine a bolt of lightning strikes the ground from a cloud above. The length of this awesome spark can be many miles long and as wide as a bus.
Between 10,000 to over 100,000 volts are generated in this instantaneous jolt. Furthermore, a single lightning bolt rarely fires just once, but as much as 100 times a second, giving it that odd “flickering” effect. As such; each and every one of those innocent “pops” evident in these recordings is one of those huge sparks just described. But as you may have already observed, there are often HUNDREDS of them per second occurring, some of them really loud, but most quite moderate to faint. They seem to permeate the background sort of like an old, worn vinyl record.
Obviously, there is A LOT of lightning going on out there. There are-a couple million lightning strokes (flashes) occur each day, worldwide, from approximately 1500-2000 lightning storms in progress at any given time. A VLF receiver is quite good at picking up lightning from as far as 3000 miles distant (perhaps more), and gives you a nice idea of the SHEER amount of lightning strokes firing off in any given second!
Tweeks: You might have already noticed a lot of the lightning static (“sferics”) seems to have odd pinging and ringing characteristics. This “tweeking” effect, sometimes quite beautiful sounding, is generally a night-time effect, with a few tweeks audible in the late afternoon/early evening and reaching their best and most numerous around midnight, and finally tapering off once sunrise occurs.
At about 50-55 miles in altitude (80-88 km), the E-layer of Earth’s ionosphere (a layer of charged particles, called “ions”) acts similar to a mirror to VLF radio waves. The same goes for Earth’s surface (more- or-less) and the two “sides” form a sort of pipeline which channel VLF radio signals, especially lightning stroke static impulses. Static impulses from very distant lightning storms (thousands of miles) can travel better at night in this huge radio wave pipeline of Earth, but, below a certain frequency, there is an abrupt cut-off, whereby the pipeline effect ceases. This is at about 1700 Hz audio frequency, which is also the frequency which most of the ringing and pinging sounds of tweeks are taking place.
Tweeks slowed down about 10 times almost begin to mimic low-pitched whistlers! Like Whistlers, one can get lost in the explanation of what causes a Tweek, and so it’s sometimes more fun just to enjoy their odd sounds. Also like Whistlers, Tweeks can sound very different from night-to-night, sometimes very pure and ringy, other nights they have a “crusty” sound. During those (frequent) times no other Natural Radio sound can be heard besides incessant static, listening to Tweeks themselves can be mesmerizing!!
Whistlers: Most people get introduced to Natural Radio by hearing a recording of a whistler. Indeed, whistlers are the most common Natural VLF Radio sound besides lightning static, especially for those listening in middle latitudes. The term “Whistler” broadly defines downward- falling sounds which range from nearly pure whistling tones to windy/breathy sounds more similar to a “sigh” than a whistle. Between these extremes are a vast variety of whistler types.
Whistlers are the direct result of a lightning stroke firing off, and usually occur 1-2 seconds after an initiating lightning flash. Very few of any lightning strokes ever produce whistlers, but enough do to make things very interesting on the good days, and sometimes whistlers are so numerous as to be called “Whistler Showers” or even “Whistler Storms.”
Earth’s magnetic-field, which keeps compasses nicely pointing in one direction only (hopefully!), plays a major role in the formation of whistlers. Not fully understood to this day, the traditional theory assumes that SOME of the radio energy from SOME of the lightning strokes in just the RIGHT location get “ducted” into channels formed along the lines of Earth’s magnetic field, travelling out into near space and to the opposite hemisphere, where they are heard as a short, fast whistler.
If conditions are favourable, some of the energy from these short, fast whistlers rebounds back the way it came to “arrive near” (within several thousand miles of) the point of its initiating lightning stroke, and becoming magically louder and longer. Essentially, during its globe- hopping round trip, the “all-frequencies-at-once” radio signal of a lightning “pop” gets the privilege of being pulled and stretched apart, with its higher audio frequencies arriving sooner than its lower frequencies, hence the downward-falling tone.
Chorus/Auroral Chorus: Another general term used to define a number of Natural VLF Radio sounds, chorus defines several types of sounds when they occur in a rapid, intermixed form. The individual squawks, whoops, barks, and chirps of “triggered emissions” tend to get lumped into the general term of “chorus” when they occur in large amounts together. Depending on the time of day, location of event (or at least where it was heard), Chorus becomes “Auroral Chorus” (it was occurring near auroral sources or during visual displays of aurora), or around the pre to post-sunrise period, when it is called Dawn Chorus.” Both sound generally similar, though chorus can manifest itself in endless variety.
Chorus is a product of magnetic storms, when events on the Sun, such as a solar flare, or “holes” on the Sun’s outer atmosphere (the Corona) allow a barrage of high-speed charged particles to impact Earth’s outer magnetic field (magnetosphere), causing it to deform and pulsate, much like air currents deform the thin film of a soap bubble. Phenomena such as Aurora (Northern and Southern Lights) also increase dramatically during magnetic storm periods, as do such natural VLF Radio sounds such as chorus.
Auroral Chorus tends to be heard more often and at generally higher latitudes than whistlers, except for the widespread Dawn Chorus, which, when heard at lower-middle latitudes, is strictly a magnetic-storm time phenomena.
Hiss: Also called “Hissband,” is a VLF radio emission partially arising directly from Aurora, with some of it emitted right from the same location as where the visible light (usually greenish in cast) is produced and usually very high-pitched.
Other hissband is generated farther out in Earth’s magnetosphere including the bow-shock region of the magnetosphere facing the incoming Solar Wind. Hiss can vary in its frequency band, sometimes it has a high-pitched sound like a slightly open water valve or toilet-tank filling up, and on other occasions can sound much like the low-pitched roar of a waterfall. While generally stable in characteristic, it can sometimes abruptly change in volume and/or pitch, indicating some sudden change has occurred in the geo-magnetic field.
Periodic Emissions: Other sounds different than whistlers or chorus get lumped into this category, but as the term implies, they tend to occur only occasionally (periodically) and in repetitious fashion with a predictable repetition time (period). These rarer Natural Radio emissions arising from magnetic storm/auroral phenomena and heard strongly only at higher latitudes such as Alaska, central or northern Canada, Iceland, northern Scandinavia, or Antarctica.
Tonal Bands: Strange-sounding hissy noises, or a multitude of whistling sounds which abruptly begin and end, usually for only 5-10 seconds in duration.
Man-made VLF emissions:
Submarine Communication: VLF radio waves being so long are able to penetrate water, so this radio frequency is often used for simple communication with submarines. Alpha is a Russian system that has three transmitters sending three short pulses of approx. 100 milli-second duration followed by a pause of a couple seconds’ duration.
50Hz hum: Power line “hum” from alternating current electric wires: Switch on a VLF receiver within your home or office, and you will not hear anything BUT this sound! Today, all electricity generated at power plants is “alternating-current (AC),” as opposed to “direct-current (DC)” produced from batteries in your watch and portable radios. With AC, the polarity changes a many times a second. In Europe, Asia, most of Africa, and Australia/New Zealand, the electric mains power changes polarity 50 cycles-per-second, or 50 Hz. In North America and in most Central and South American countries, it is at 60 Hz.
While convenient for long- distance transmission and easy voltage transformation, AC generates hum in poorly filtered audio equipment and especially in VLF receivers! If this wasn’t bad enough, most electrical “grids” seem to cause the 50 of 60 Hz current to generate harmonics – multiples of 50 of 60 Hz, causing hum/buzz THROUGHOUT the VLF radio spectrum. Those immense, high-voltage, high-tension electric wires sagging between the tall metal pylons can generate impossible amounts of hum and buzz if you try to listen with a VLF receiver too close to them.
To have “hum-less” recordings of VLF phenomena, you have to find sites far removed from above-ground power lines. It’s fairly easy to find absolutely quiet hum-free listening spots in desert and mountainous or tundra regions of North America, Australia, or the remoter parts of Europe and the British Isles (Scottish Highlands particularly) if you’re willing to make a few days of it, but finding quiet spots to listen close to home and/or in populated regions such as the English Midlands or U.S. east and midwest (including farmed areas away from towns) usually mean pesky power lines will be around somewhere, usually alongside the road you’re travelling along.
The above sound descriptions was originally written by Stephen P. McGreevy, of whom I consider to be a pioneer of modern day VLF radio listening and probably the most knowledgeable person on the subject. View tons more info at Stephen’s website www.spaceweathersounds.com.
Can you hear the northern lights with your own ears?
For centuries strange noises have been said to accompany the exquisite curtains of colour seen in the sky near the Earth’s magnetic poles. These sounds are heard often enough to be known as the “whisper of souls of the dead” in Eskimo folklore (see our folklore page), amongst other things. However for many years the existence of these sounds has been the subject of much debate. Some people hear the swish of the aurora while others nearby are left in silence. As a result the auroral noises were often written off as a psychological illusion.
In recent years however scientists believe that they may have discovered what causes the auroral whispers. Aurora are created as the Earth’s magnetic field captures charged particles from the solar wind. During these electrical “storms”, scientists have recorded abnormally high electric fields and believe that they are responsible for the noises auroras emit. They suggest that they cause “brush discharge”, which occurs when electric fields induce an electric potential gradient in objects on the ground. If these objects have points or spikes-such as those on leaves or pine needles, for instance-there can be an electric discharge at their tips that can create an audible crackling.
However a scientist named Keay, believes that the electric fields are rarely strong enough to create brush discharge. He feels that the whispering of the auroras have another cause. He believes that just as with meteor noises, auroral sounds are generated by very low frequency electromagnetic waves (which is exactly what our system is recording), and it is these waves acting on transducers such as hair. These waves seem to be produced by ions and electrons from the solar wind that are reflected back and forth in the Earth’s magnetic field.
What do we think?
Both descriptions sound plausible to us. Since I have been researching and setting up our VLF radio system, the first thing that struck me when I first powered it up was that the sounds it creates is almost exactly as the folklore and legends describe. They almost always say they hear “whispers and crackles” watching an intense northern lights show. So this suggests it was probably a large geomagnetic storm they were watching, and somehow, the human ear may have inadvertently picked up VLF waves, as whispers (what we probably call whistlers) and crackles are heard on the VLF stream above. Alternatively a strong geomagnetic storm (and if the conditions are right) then brush discharge is a real consideration. From what I have read on the subject the sounds can emanate from surrounding materials such as trees, or indeed from the air itself, which again, is what people have described as happening.
We will be spending a lot of time in Lapland in the next few winters under the northern lights, so this is one part of them we will be studying. Perhaps by the end of winter we will have an answer to the age old question; can you hear the northern lights?
One thing is for definite, it’s still mysterious.