Whistler Ducting is the ability for very low frequency waves caused by ______ , to travel through the atmosphere when conditions are perfect [read: irregularities are present] in the Ionosphere and Magnetosphere.
Yep. Actually, ducting can take place (or be fabricated) so that you can use HF instead of just VLF in the duct.
Ducting is a really complex subject. Think of it as sort of building a fiber-optic sort of conduit for radio signals out of upper atmospheric conditions. In a similar way to fiberoptics, the signal will tend to remain in the duct because it sees reflections at the duct boundary due to refractive index differences. The duct is generally only good for small ranges of radio signal frequencies.
So can humans use them for wave propagation?
They can and do, but for RADIO wave propagation, not sound. Sound is not radio, radio is not sound. They are totally different in pretty much every way possible.
Yet in 1972 there were classified theories on their generation by the military?
You betcha. Duct generation, maintenance and collapse are big big topics, and the subject of much research at such installations as, say, Gakona. That would be one of the things they actually DO there which you don't hear so much about. Why, you may ask. Well, mirrors are nice. You can make a nice plasma mirror in the ionosphere and use it to peek over the horizon in radio spectra much like a kid does with the mirror in his toy periscope.
Ducts, on the other hand, would allow you to sneak an "ear" over the horizon and park the other end right over, say, a military base, or an area of conflict, or your neighbor's capitol. Or you could establish, say, a nearly undetectable comm circuit to some of your troops in the field, with the signals being confined to the duct except at the end points. Or you could collapse other people's ducts to keep them from doing the same. Or after a nuclear blast tears up the ionosphere temporarily, you could still communicate by punching ducts. There's a LOT of military use for on-demand ducting.
So, if we can create an irregularity in the ionosphere/magnetosphere, we should be able to direct propagation of VLF waves?
VLF RADIO waves. Not VLF sound waves. Sound is not radio, radio is not sound.
So, what was it that HAARP does again? Wouldn't 'exciting' the ionosphere cause any irregularities?
Yep - and ducting is in fact studied there, but not just there. Not so much VLF ducting though. It's interesting to study, not so useful in practice.
Now that it is excited, can we generate VLF waves somehow and use them for geophysical surveying?
A swing and a miss. Ducting and ELF/VLF generation by the array are two different things. The "geophysical surveying" bit, such as it is, is more directed towards magnetotelluric mapping. Think of it as onshore CSEM with the source being elsewhere. OTOH, you can just wait for sundown and get the same effect.
Using that for sub communications was as being explored as a backup to Seafarer at one point, however, you can't always generate VLF or ELF at Gakona, it depends on conditions in the electrojet. It comes and goes. In the end, Navy dropped ELF as a communications medium to subs altogether and closed down Seafarer. These days they use VLF and "other things". You can get VLF from really big towers - you don't need a Seafarer setup to do it. If you look in the right places in Australia you can see lots of them we use these days.
Could the sounds people are hearing be ducted VLF waves aimed at surveying the continent for structural deficiencies?
No. You can't hear radio, because it's not sound.
Just wanted to make the connection between ionosphere/magnetosphere > VLF wave propagation > loud rumbling sounds. I guess that's the point of this thread - I am looking for ways the magnetosphere/ionosphere are influenced and how this relates to loud rumbling sounds...
Well, that'll be tough, because really the ionosphere doesn't MAKE sounds. I think where you're getting confused is the usual thing I see on ATS from about 30% of the posters, where they have a hard time understanding the differences between EM waves and sound. So they read about "waves" that have "frequency" and it all mushes together for them as one co-equal thing. It's not, though.
It is widely known that humans can hear as low as 20khz. VLFrequencies are typically within a range of 3khz - 30khz. Other websites like this one Auroral Chorus claim the maximum is 10khz, which would be too low for us to hear....
You hear sound. Sound is caused by compression waves in a medium, in most cases air. Since air has elasticity, a disturbance in air causes longitudinal waves of compression and rarefaction to propagate away from a source. If the waves of compression have frequencies in a range we can hear, say 20-20000Hz, then if they have enough amplitude, you can perceive them as sound.
You cannot hear radio waves by means of your ears. Ears are designed to pick up compression waves in air. Propagating radio waves are transverse instead of longitudinal, and instead of being a wave of compression of air like sound, they consist of an electric field and a magnetic field at right angles to each other.
Despite the fact that you can have a radio wave at, say, 10kHz, and a sound wave at 10kHz, it doesn't render the radio wave audible, and you can't pick up the sound wave on a radio receiver, because sound and radio are not the same thing at all.
So is ducting something that can be created to serve the HAM operator, or just a natural phenomenon that HAM operators sometimes encounter?
For HAMs, it's an intriguing natural phenomenon. For the military, it's a goal.
@mr-lizard:
May be unrelated, but 'acoustic charge transport' is a term worth researching.
Totally unrelated. Charge transport on the surface of piezo materials has pretty much nothing whatever to do with any of this.
