[HN Gopher] "Frost crack" sounds may come from sky, not trees
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"Frost crack" sounds may come from sky, not trees
Author : jnord
Score : 252 points
Date : 2024-08-13 22:44 UTC (4 days ago)
(HTM) web link (nautil.us)
(TXT) w3m dump (nautil.us)
| Xeyz0r wrote:
| Interesting, but kinda hard to believe that the sounds we hear in
| the forest could be coming from that high up I'm no expert, but
| if that's true, that's pretty mind-blowing
| maxbond wrote:
| The article explains that this objection was raised by other
| researchers, but that the sounds were triangulated to a height
| of about 250 feet (because they are caused by an electrical
| interaction at the top of an inversion rather than from the
| aurorae directly).
| ditn wrote:
| One thing that I found super interesting when I studied audio
| engineering is that our ears are very good at determining
| direction left/right, but absolutely hopeless at working out if
| a sound is up or down.
|
| This makes their hypothesis a lot more believable to me; I can
| understand others incredulity.
| ambicapter wrote:
| > absolutely hopeless at working out if a sound is up or down
|
| Easy, just turn your head to the side :P
| yosito wrote:
| Fascinating read! I'm surprised this wasn't already commonly
| known.
| pierrec wrote:
| The conference paper (which is very well written and
| approachable) suggests that the precision of instruments was
| insufficient to establish this as of 20-ish years ago. See the
| section "First Experimentations":
| https://www.researchgate.net/profile/Unto-Laine/publication/...
|
| Trivia: I tried to copy "First Experimentations" directly from
| the pdf and this what came out of my clipboard:
| -*%.$+/01/%*2/#$3$**&#. Thanks, Researchgate
| smegsicle wrote:
| more like research gatekeeping amirite
| yorwba wrote:
| Several chunks of text in that PDF start with the printable
| ASCII characters from ! onwards in order until there is a
| repetition, e.g. _Magneto-acoustic triangulation_ from the
| headline corresponds to
| !"#$%&'(")'*+&,)-&.,"$#*/"&,'$
|
| which is >>>
| list('!"#$%&\'(")\'*+&,)-&.,"$#*/"&,\'$'.encode('ascii'))
| [33, 34, 35, 36, 37, 38, 39, 40, 34, 41, 39, 42, 43, 38, 44,
| 41, 45, 38, 46, 44, 34, 36, 35, 42, 47, 34, 38, 44, 39, 36]
|
| So I think this is probably a PDF font-encoding issue that
| might've already affected the author's original upload.
| pierrec wrote:
| You're right, I immediately assumed some annoying DRM, but
| after looking it up, it does seem more like a bug. I
| couldn't find any clear explanation for why it happens
| though.
| timcobb wrote:
| Would be cool if there was a recording, I don't know what this
| article is talking about.
| maxbond wrote:
| Surely the recordings are available somewhere on the web, but
| here's a short clip I found on YouTube:
|
| https://youtube.com/watch?v=cm97VQobbh4&t=435
| mistercow wrote:
| Wouldn't the tree explanation be refuted by simply recording the
| sounds in an open field, far away from trees?
| florbo wrote:
| But what if the discharge requires some specific environmental
| factor, say, something the height of a tree?
| greenbit wrote:
| Maybe tree covered ground makes a more effective source of
| the rising-up component of this process. That relatively
| warm, negatively ionized rising air might be much diminished
| over a frozen lake or open plain. Otoh, it'd probably be
| _greater_ over the ocean, I would think.
| satori99 wrote:
| Do people at Antarctic research stations ever hear this sound?
| bongodongobob wrote:
| Probably not as it requires a gradient, which that deserted
| and static landscape wouldn't provide.
| Willingham wrote:
| In grade school I read a book called 'The Hatchet'. It was a
| story about a man who survived a plane crash near the arctic
| circle and had survived many days on his own with not much more
| than a hatchet. He experienced these sounds after a number days
| in the harsh wilderness and thought it was gun shots and that he
| was going to be saved. The book then went on to explain that it
| was the trees cracking from the extreme cold. I was mesmerized by
| this as a kid. Knowing now the true origin of the 'frost crack',
| I'm twice as captivated.
| j_bum wrote:
| A small nitpick, the main character is only 13 years old. Great
| book!
| wyager wrote:
| If he read it at the same age range I did, then a 13 year old
| certainly seemed like a man by comparison.
| teruakohatu wrote:
| A good book, I also read it as a child.
| ARob109 wrote:
| That's the alternate story line as told in Brian's Winter. He
| did not ordeal the winter in The Hatchet.
|
| One of my favorite books as a kid, just recently read Hatchet
| to my boy
| move-on-by wrote:
| I just read the synopsis, I'm curious what age your son is or
| how old you were when you read it? I'm not sure my son is old
| enough for it.
| ninkendo wrote:
| Not OP but Hatchet was an assigned book when I was in 5th
| grade (American Midwest school), it's pretty common for
| early school age kids to read. It's got some slightly
| intense scenes in it, but nothing that 5th grade me was too
| scarred by (the scene where he has to go into the lake to
| get something from the plane and sees the corpse of the
| dead pilot was pretty scary to 10-year-old me but that's
| about as bad as it got.)
| wombat-man wrote:
| Yeah I think it was 6th grade for me, which I think is
| about right.
| Slump wrote:
| Hatchet was one of my favorite books growing up. I believe
| the first time I read it I was in 4th grade if that helps
| you gage (it was pretty common in 4th and 5th grades if I
| recall correctly). That said, my mother was a librarian and
| didn't care what I read as long as I was reading (including
| Faulkner and East of Eden when I was in 6th grade which was
| way too mature for that age :-)) so depending on your son
| maturity your milage may vary. That said, Hatchet is a
| great a book and I give it some credit to my life long love
| of the outdoors and adventure.
| lynndotpy wrote:
| I think it's appropriate for as soon as your son would like
| to read it. I read it in third grade, even though it was
| introduced in fifth.
|
| Speaking from memory, I really appreciated being able to
| read books with relatively "mature" topics like that
| (isolation, survival, etc.)
| klyrs wrote:
| I found Hatchet when I was in grade 4, and damn near read
| it straight from the library checkout counter until I was
| done a few hours past midnight. I'm pretty sure that my
| parents made me take a break for dinner.
| m8s wrote:
| That reminds me, there's a really great survival game called
| The Long Dark in which you survive a plane crash in something
| like the arctic circle and must survive. If anyone is into
| survival games, definitely check this one out!
| jnurmine wrote:
| It's an extremely captivating game with an unparalleled
| atmosphere.
|
| Before I started playing the game, I saw in passing an in-
| game video of a well-stocked gas station. Lights were lit and
| shelves were stocked. It was made like an in-game
| advertisement of some sort.
|
| Later, when I started to play the game, I recalled the video,
| and decided to reach the gas station and set up my base
| there. Imagine the food! The warm indoor temperatures! Brand
| new clothes!
|
| After a perilous journey I reached the gas station. For some
| reason I was expecting the lights to be on and warmth, but of
| course I was greeted by a half-broken gas station, no lights
| of course, shelves were almost empty and cold indoors.
|
| But it was a good base, lots of loot.
| theoreticalmal wrote:
| Was that the Quonset hut surrounded by wolves? I think on
| the broken highway map?
| jnurmine wrote:
| Yes, Quonset Garage on the Coastal Highway.
|
| It was maybe this video, or a clip of it:
| https://www.youtube.com/watch?v=gs2IYnNBVhQ
| mock-possum wrote:
| There was another novel along the same lines I remembering
| liking as a kid called "my side of the mountain"
|
| A story about a kid basically muddling through living 'off-
| grid" before it was cool.
| DiggyJohnson wrote:
| My Side of the Mountain, The Hatchet, and Peak were like the
| trilogy of adventure books for our cohort I think.
| exabrial wrote:
| I blame my side of the mountain for me, sitting right now, in
| Breckenridge about to head out into the woods for the day.
|
| Absolutely captivating book to read as a kid.
| msla wrote:
| "Hatchet" by Gary Paulsen
|
| https://en.wikipedia.org/wiki/Hatchet_(novel)
| Loughla wrote:
| I got to meet Gary Paulsen at a conference once. He's a legit
| mountain man, and one of the absolute nicest people on the
| face of the earth. He stayed at a book signing for like 6
| hours after to talk to fans. Super cool guy.
| Waterluvian wrote:
| Hatchet is part of a series. They're all pretty good.
|
| The one thing I remember is how he found a rifle and ammo but
| eventually went back to the bow because it's quieter and ammo
| is reusable. What a gamer.
| dieselgate wrote:
| Think I used Hatchet for a book report every year from like 3rd
| to 7th grade.
| karaterobot wrote:
| > It's not to say that trees don't crack--but rather that spooky
| noises long attributed to trees may emerge from the night sky
| itself.
|
| Well, it seems like he demonstrated that the night sky itself can
| make sounds under certain conditions, not that these sounds are
| always the night sky.
|
| By the way, I don't recall ever hearing the supposed tree
| cracking sound in an area where there were no trees. If it's
| always just the sky, you'd expect to hear it at least
| occasionally on the plains, or coming from 250' in the air above
| you when you're on a frozen lake.
| dylan604 wrote:
| > or coming from 250' in the air above you when you're on a
| frozen lake.
|
| If you're on a frozen lake, you much prefer the crack coming
| from above than below.
| greenbit wrote:
| And then of course, there are the "ice making" sounds that
| _do_ come from below. And different lakes and ponds even seem
| to have somewhat different voices in that way.
| idatum wrote:
| And something equally chilling -- the sound of a glacier
| cracking (more of a deep thud sound).
| maxbond wrote:
| I think that framing comes from the article rather than the
| Aurora researchers (I skimmed some of their papers & didn't see
| it mentioned), but the article claims:
|
| > Indeed, these loud cracking sounds are often attributed to
| large pressure splits in tree trunks, caused by sap freezing
| and expanding inside the tree's interior. But while freezing
| sap in trees has been found to produce sounds at ultrasonic
| frequencies, outside of the range of human hearing, scientists
| have found no evidence this phenomenon might make sounds that
| are audible to the human ear.
|
| Though if you told me you'd heard a tree make a groan or a
| crack, I'd be inclined to believe it, it doesn't strike me as
| outlandish.
| RHSeeger wrote:
| That quote seems odd to me. Specifically,
|
| 1. The sound is attributed to trees cracking
|
| 2. The cracking is caused by sap freezing and expanding
|
| 3. Sap freezing produces sound in the ultrasonic range
|
| 4. So it's not the trees
|
| Point 4 is not a valid conclusion from 1-3, because it was
| never stated that the sap freezing is what is being heard.
| Rather, it's the trees cracking, which is _caused_ by the sap
| freezing... but its own thing with its own sound.
| nardi wrote:
| I think you missed the last bit:
|
| > scientists have found no evidence this phenomenon might
| make sounds that are audible to the human ear.
|
| Which I take to mean they've measured ultrasounds but no
| audible sounds.
| bmicraft wrote:
| "Found no evidence" and "didn't even try to measure"
| isn't really the same, is it?
| tbugrara wrote:
| Point 4 seems to have been made by you, not the article.
| rini17 wrote:
| Depends whether the landscape is prone to inversions. They
| happen most often in wide and enclosed valleys.
| slashtab wrote:
| Maybe trees are affecting the rate and intensity of Inversion.
| nuc1e0n wrote:
| Well thunder and lightning comes from the sky and lightning is
| caused by static effects of ice crystals in thunder clouds. So
| maybe it's something similar.
| mattdesl wrote:
| Really fascinating. After reading a little more, I learned that
| while Laine proposed the inversion layer hypothesis in 2016, the
| Auroral Acoustics group he headed was informally started in 2000.
| The reason the linked article is coming out now is due to Laine's
| latest paper that details the triangulation of the sounds[1][2].
|
| Would love to try and record this myself. I've been recording
| some VLF "sferics" for some time now for an art project[3]; it
| seems the auroral sound recordings often peak in the same
| frequency range (and perhaps there is overlap without me
| realizing it).
|
| [1] http://research.spa.aalto.fi/projects/aurora/index.html
|
| [2] https://www.researchgate.net/profile/Unto-
| Laine/publication/...
|
| [3] https://www.mattdesl.com/sferics
| goda90 wrote:
| At first I thought this was going to be about frost quakes[0],
| which are mini quakes we get in the Midwest when there's a deep
| cold.
|
| [0] https://en.wikipedia.org/wiki/Cryoseism
| whatshisface wrote:
| > _As this warm air collides with cooler air from above, it forms
| an "inversion" layer of warmer air layered over cold air, which
| traps the ions._
|
| I think this is reversed, inversions are usually cold air sitting
| atop warmer air. (Warmer air is lighter, defining the typical
| sequence with which an inversion is relative to.)
| histriosum wrote:
| You aren't quite right here. Temperature inversions are when
| the atmosphere warms as you go up instead of cools. The
| atmosphere usually cools at a fairly constant rate as you go
| up, at least in the troposphere. This layer of warmer air aloft
| acts as a cap, limiting vertical motion from rising air parcels
| from below (which are cooler than the air aloft and thus cannot
| rise through the inversion).
| soared wrote:
| You are correct afaik - warm air would not trap cold air below
| it as it would move up, only a layer of could air could trap
| warm air below it.
|
| Some visualizations show air cold/warm/cold, where as others
| are just warm air under cold air.
| e44858 wrote:
| Inversions usually happen when the ground is cooling faster
| than the air above, due to radiative cooling. That results in a
| layer of warm air sandwiched between cold air above and below.
| aaron695 wrote:
| > Laine was able to _triangulate_ the origins of the sounds from
| calculations based on the distance between the microphones and
| the speed of sound. The triangulation data revealed the origin of
| the sounds was indeed the sky.
|
| Triangulate doesn't work, it's in the sky remember?
|
| You need 4 for 3D space _theoretically_. But in practice it 's
| more like 6-7. Any wind or temperature difference adds dimensions
| which you have to computer away.
|
| The paper seems to confirm it's literal. 3 mics. Which is fine to
| find stuff but why not do it to spec in the real paper, do the
| results disappear?
|
| They talk about "virtual microphones", not convinced.
| lrasinen wrote:
| Three mics and a loop antenna. The diagram in the May 2024
| implies the mics provide a trajectory and antenna-mic
| difference fixes it in 3D.
|
| Disclaimer: I was in his Basics of Speech Processing class in
| the university. One of the best (and funniest) courses I had.
| sho wrote:
| This reminds me of "aircraft wake snapping" or "vortex snapping",
| which is a very audible sound one can sometimes clearly hear
| shortly after a plane passes over you if it's low enough, such as
| on final landing approach. I seriously thought I was imagining it
| the first few times I experienced it - so weird to hear sound
| coming from apparently empty air.
|
| edit to add an example: https://www.youtube.com/watch?v=UA-
| NONhZIN8
| zakki wrote:
| For someone living in equator the article will be perfect if it
| has the sound mentioned in the article.
| vnorilo wrote:
| First I heard prof Laine talk about recording auroras in the
| early 00s I and many of my student friends thought he was an old
| eccentric (in some less polite words too).
|
| Seeing him come through with such a solid long term effort,
| rigorously done and communicated with clarity is amazing, with a
| pinch of healthy embarrasment.
|
| (I studied in the same academic cluster of music/audio/acoustic
| labs he made his career at)
| sethammons wrote:
| My first thought was "bullshit, these are _obviously_ trees
| cracking." Well, using triangulation, it is _obviously_ coming
| from 250+ ft in the air. Good to test assumptions!
| sandworm101 wrote:
| >> Indeed, these loud cracking sounds are often attributed to
| large pressure splits in tree trunks, caused by sap freezing and
| expanding inside the tree's interior. But while freezing sap in
| trees has been found to produce sounds at ultrasonic frequencies,
| outside of the range of human hearing, scientists have found no
| evidence this phenomenon might make sounds that are audible to
| the human ear.
|
| Personally, i have not just heard them but have seen it happen.
| At -40 and below, in certain evergreen forrests not used to such
| temperatures, a tree can randomly "explode". An internal crack
| shakes the tree, throwing snow everywhere. It lookes and sounds
| like an explosion. You hear gunshot and then see the tree shake
| off all its snow. The tree stands out as the one dark with
| branches no longer held down by snow. It is like an angry ent
| waking up about to eat a passing human.
|
| https://youtube.com/shorts/oG-N2LCYEc4
|
| Does anyone really believe that a crack like that wouldnt make a
| gunshot sound?
|
| Here is the sound, after about 0:30. Not much snow to shake off
| but you can see them moving.
|
| https://youtu.be/Rz3TqqNkEBU?feature=shared
| krona wrote:
| I'm amazed that this phenomena is hitherto unexplained when it's
| entirely common knowledge in rural scandinavia, barely worth
| talking about.
| tnias23 wrote:
| What's common knowledge in Scandinavia? That the sounds come
| from the air, not the trees?
| snozolli wrote:
| In February 2021, in the Willamette valley of Oregon, we had a
| weather event unprecedented in my lifetime. Winters here are
| usually overcast and rainy, with little to no snow and a handful
| of mild freezes. In 2021 we had a significant rainfall followed
| immediately by a deep freeze due to a polar vortex.
|
| That morning was like nothing I've ever experienced. About once
| per minute there would be a loud crack like a gunshot, coming
| from all directions.
|
| After several days, power was restored, the roads were cleared,
| and it was obvious what happened. Countless deciduous trees had
| split from what I assume was the accumulated water from the
| preceding rain storm. There were so many downed and permanently
| damaged trees that it took around a year for property owners and
| the city to finish cleanup.
|
| Usually, when we get freezing temperatures, it's because there's
| no cloud cover. It's extremely unusual to swing from heavy
| rainfall to a deep freeze like that.
|
| Anyway, I don't know if this article is talking about something
| different, but the cracking I heard was definitely deciduous
| trees cracking due to expanding, freezing water. Few conifers
| were damaged.
| RecycledEle wrote:
| Nonsense.
|
| If you hear a loud crack and are near trees, look up and get out
| if the way.
|
| This idiot is going to get people killed.
| __MatrixMan__ wrote:
| Is it possible that the inversion layer creates a structure for
| sound to reflect/refract back down towards the sensor, when it in
| fact the original source was on the ground? You might not detect
| it laterally if there were a bunch of trees in the way.
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