Mystery Sounds From Storms Could Help Predict Tornadoes (theguardian.com) 34
Mysterious rumbles that herald tornadoes could one day be used to predict when and where they will strike, according to researchers. From a report: Storms emit sounds before tornadoes form, but the signals at less than 20Hz are below the limit for human hearing. What causes these rumbles has also been a conundrum. Now researchers said they have narrowed down the reasons for the sounds -- an important factor in harnessing the knowledge to improve warnings. "The three possibilities are core oscillations [in the tornado], pressure relaxation, and latent heat effects," said Dr Brian Elbing, of Oklahoma State University, who is part of the team behind the research. "They are all possibilities because what we have seen is that the signal occurs before the tornado touches the ground, continues after it touches the ground, and then disappears some time after the tornado leaves the ground."
The latest work was presented at the annual meeting of the American Physical Society's Division of Fluid Dynamics in Seattle. The low-frequency sound produced by tornadoes has been known about for several decades, but Elbing said a big problem has been a lack of understanding of what causes the sounds, and difficulties in unpicking them from a tornado and other aspects of the weather. The subject has seen renewed interest in recent years, with Elbing saying it could prove particularly useful for hilly areas such as Dixie Alley, which stretches from Texas to North Carolina. "Infrasound doesn't need line of sight like radar, so there is hope that this could significantly improve warnings in Dixie Alley where most deaths [from tornadoes] occur," he said.
The latest work was presented at the annual meeting of the American Physical Society's Division of Fluid Dynamics in Seattle. The low-frequency sound produced by tornadoes has been known about for several decades, but Elbing said a big problem has been a lack of understanding of what causes the sounds, and difficulties in unpicking them from a tornado and other aspects of the weather. The subject has seen renewed interest in recent years, with Elbing saying it could prove particularly useful for hilly areas such as Dixie Alley, which stretches from Texas to North Carolina. "Infrasound doesn't need line of sight like radar, so there is hope that this could significantly improve warnings in Dixie Alley where most deaths [from tornadoes] occur," he said.
Green skies up above (Score:4, Interesting)
Back in 2012, I was visiting my wife's family in Argentina, in a smaller city ~500Km from the capital. A storm was approaching. Her sister said, "hmmm, the sky looks green. We will have hail."
Five minutes later, we were having the strongest thunderstorm I have ever seen. Dozens of trees were uprooted, cars were smashed.
And, of course, there was hail. Lots of it.
Re:Green skies up above (Score:5, Informative)
That's pretty normal here in tornado alley(central US to the US east coast through to southern ontario), usually any weird colours like that mean GTFO and head for a basement/inside room of a building or when driving look for a ditch. Pink and yellow clouds happen too usually with downbursts, seen trees snapped in half and trucks knocked clean off the freeway from them.
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They can predict them reliably by thermal imaging the clouds, the ground those clouds will pass over and of course the shape of the terrain and how that impacts those airflows. Combine all three from orbit and there should be no problem in forecasting the size and time of the tornado, it's duration and direction, to some degree of accuracy, dependent upon how accurate that thermal mapping is of atmosphere and ground and of course the land contours and nature, trees et al to alter and slow wind patterns. Dur
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Thermal imaging isn't a thing that exists everywhere even at radar installations and whatnot. A lot of places are just starting to upgrade into dual polarization and extending the low and mid-bands for tornado warnings 105-120km(65mi-75mi) to 240km(150mi) . And in places like the US plains and rural Canada thermal imaging will likely never be a thing beyond storm chasers who follow and watch developing storms. Which are one of the big post-storm ways that both Environment Canada and the National Weather
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Re: Green skies up above (Score:2)
Frequency Spectrum Analysis Yields Results (Score:3)
News at 11. FFT plots too.
I'm curious as to how soon the Tornado storms vs non-tornado storms diverge on the frequency spectrum. My one of our undergrad controls labs were finding which cylinder had a broken spark plug with just the FFT and matlab.
I get why distinguishing the sound is important... (Score:2)
I get why distinguishing the sound is important, but why do you need to know what causes it in order to make use of it? Isn't it enough just to make lots of recordings of it, track whether a tornado occurred or not, and analyze the sounds to determin
Re: I get why distinguishing the sound is importan (Score:4, Informative)
If you know the mechanism that causes the sound and can conclusively tie it to tornado formation, you can start looking for causes of that mechanism, potentially allowing you even greater predictive capability.
And you won't even need dorothy.
False claims in the first sentence... (Score:2)
signals at less than 20Hz are below the limit for human hearing.
False. You can perceive well down to single digits [wikipedia.org] of frequency. It takes more SPL, but 10-15 Hz is readily audible, easily heard with enough SPL.
Re:False claims in the first sentence... (Score:5, Funny)
You can perceive well down to single digits [wikipedia.org] of frequency.
Well, it seems that the storms are emitting the Brown Note [wikipedia.org].
That might explain why tornadoes scare folks shitless.
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signals at less than 20Hz are below the limit for human hearing.
False. You can perceive well down to single digits [wikipedia.org] of frequency. It takes more SPL, but 10-15 Hz is readily audible, easily heard with enough SPL.
Humans perceive frequencies less than 12 Hz, but not as sounds; instead they are felt as vibrations (not sounds per se) in the body. The normal lowest frequency for hearing (as opposed to perceiving) is double digits [wikipedia.org]
. The Wikipedia paragraph you linked to has used the word perceive and not sound quite deliberately. I could provide citations for this but a simple search in Google Scholar gives so many results why bother?
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I feel it in my chest. (Checked with headphones) (Score:3)
*I* checked and *I* cannot hear 20Hz or lower via quality headphones. If I put my finger on the headphones I can feel it.
Through loudspeakers, I can feel it in my chest at frequencies I can't hear with my ears.
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Re:I feel it in my chest. (Checked with headphones (Score:4, Informative)
Obviously if I had a tone generator at 2 Khz, and I tuned it off and off at 1Hz, you'd notice the sound turning on and off once per second, right?
You may have noticed if two instruments play the same note at the same time, but they aren't tuned exactly the, you get a wahwah effect. That happens when two sounds are close to the same frequency, but not quite the same frequency (within about 1.3:1 ratio).
Hensel et al played tones at 1.6 Khz and 2.0Khz, within ratio to create that effect from hearing two sounds at once, due to the interaction between the two wave forms. The effect is that the 2Khz tone CHANGED 6 times per second. Just like if you turned the tone on and off once per second. Hearing a 2Khz tone change 6 times per second is not the same thing is hearing a 6Hz tone.
Primary frequencies were fixed at f1 = 1.6 and f2 = 2.0 kHz with fixed levels L1 = 51 and L2 = 30 dB SPL. A new measure, the
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I can hear 0.0000017 Hz (Score:2)
Every week at noon on Saturday, they test the local tornado siren. Once per week, so that's 0.0000017 Hz.
By your way of thinking, I'm hearing 0.0000017 Hz.
Most people would just say I hear the 3Khz sound once a week.
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Rewd even the abstract of the paper. Tones of 1.6Khz and 2.0Khz....
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Re: False claims in the first sentence... (Score:2)
The distinction is not easy to make. Maybe itâ(TM)s a continuum then? The LF pressure gradient can definitely be perceived. Large enough gradient will blow your ears and that would be very painful.
That has little to do with hearing (even though it involves some of the organs), and itâ(TM)s all about the cavities and pathways (and how well they work in balancing the pressure) in oneâ(TM)s head.
Itâ(TM)s like when diving or being on an ascending or descending airplane (hopefully youâ(T
Carl and Jerry (Score:2)
Business (Score:1)
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