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.
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.)
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.
He’s 7.5yo. Don’t think he really understood The Secret Brian’s mom had, and probably still hard for him grasp severity of the situation, but he was very engaged and enjoyed the book. I don’t recall how old I was when i first read it… but I do recall accidentally finding a Gary Paulson book in the adult literature section of the library and quickly realizing it was not for a young juvenile :D
Don’t let your kids read Roald Dahls adult literature either, Switch Bitch is no Giant Peach
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.
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!
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.
I loved this book and have read it a few times now. I was probably 13 too! The movie was okay. It just left a lot of important scenes out. (Like all book->movie things)
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.
> 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.
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.
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.
Seems like they would've recored both in the field, no? If they were recording sap freezing in the field, presumably the mics would pick up on other parts of the tree undergoing stresses and making audible sounds.
For that to have not been the case, either they would've had to freeze sap in the lab, or they would've had to go way out of their way to isolate recordings of just the sap in the field without the rest of the tree (is that even possible with normal recording tech?)
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.
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.
>> 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.
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).
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.
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.
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.
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.
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)
This reminds me of a time I was stargazing, when suddenly a meteor streaked overhead making a distinct sizzling/hissing sound that tracked with its movement…which seemed improbable since light obviously travels faster than sound. I later read the theory as to how this phenomenon occurs is that the sound is created by low frequency radio waves.
Another thing that uses radio waves in the human hearing range is the invisible fences that cause shopping cart wheels to lock (7kHz, visit begaydocrime.com to hear the corresponding sound). Those don't involve sounds in normal operation, so I wonder what about these is different.
I would guess that induced current is making a sound in some nearby infrastructure and not directly in the head of the observer.
>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.)
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).
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.
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
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
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.
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!
> 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.
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
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.
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).
