Why is the surf louder at night?
You know the drill. You arrive at the campsite at night, setting up to the rhythm of thumping waves. And it sounds huge! You sleep restlessly; the pounding sets playing on your mind.
But in the morning when you finally trek over the sand dunes, the surf is far smaller than it sounded under the cover of darkness.
Was it a mystery swell? Did the surf peak overnight?
No, the noisy surf is all related to the way sound travels through air.
The earth's atmosphere is stratified into several layers. The lowest layer of the atmosphere, known as the troposphere, is heated during daylight hours by convective processes at the earth's surface. As we ascend into the atmosphere, the temperature generally decreases with height.
But as the sun sets, the earth's surface releases energy back into space, in a process known as terrestrial radiation. This cooling effect is most pronounced under clear cloudless skies.
At night the air directly above the ground becomes cool, with warmer air aloft. This is known as a temperature inversion, and is the key ingredient to the mystery of the loud surf.
In the same way we all know how waves refract (bend) towards shallow water - for example around a headland - sound waves also refract towards cooler air masses, because colder air is denser and has a higher refractive index.
Therefore, the sound of a breaking wave will initially spread outwards but ultimately refract back towards the earth as it feels the effects of the cooler, denser air mass (see second chart, right).
This funnels the sound along the ground, amplifying the volume of the surf - and therefore giving the perception that the surf is bigger - compared to daylight hours when the airmass close to the surface is warmer, and the sound waves bend upwards to the sky away from us (see first chart, right).
Growing up in South Australia and camping at many remote regions, I'd always get overly-excited at the sound of the overnight swells. So now you know the reasons behind this phenomena, you can sleep a little more peacefully! //CRAIG BROKENSHA
Comments
Good one Craig. I have spent six months camping on the coast around the country and sometimes the smallest waves are the loudest. A single, long-period wave breaking as a shorey is way louder than 10'-12' reef break with multiple lines breaking
Yes I was almost going to add this in as well.
Smaller shorey waves exploding on the shallow sand generally make more noise than the deep rumble of a groundswell.
you guys are kooks, During the day everyone is talking and driving there cars, so we hear less of the surf and more of the white noise that surrounds us , At night less noise = louder surf ,
Mate it's science, and you are the cook. Out in the country away from cars/people/traffic is where this article was mainly referring to, not in a bustling city.
haha OMG , Deeeer ! I was taking the piss..... and yes I am a cook , Well chef anyway...
Sorry, in joke with my mates, re cook/kook.
"is heated during daylight house by convective processes at the earth's surface. As we ascend into the atmosphere, the temperature generally decreases with height."
What are you on mate, daylight house & ascending? Nah cheers, always thought it was just less other noise at night, or being in a quiet place during the day. Having a good run Craig
Ha! Well spotted.
Haha, still high from Tame Impala last night, cheers.
What about wind direction. I'm guessing this depends on wind still or onshore conditions.
With an early morning offshore the surf can often be barely heard even if it's huge.
Yeah that's also a factor too. Though air density is more interesting :)
Sound is a longitudinal wave in which uses air as its medium to travel. A vibration of particles in the air (magnitude of the vibration determines how loud the sound is) bump the surrounding particles which in turn bump the next particles to cause a vibration in them, and thus a noise. Since wind is the net movement of air particles, an offshore breeze makes the sound wave require more energy to move along a set distance as a vibration of equal magnitude in which travels with an onshore breeze. This is due to the net velocity of air (say 25km/h) in an offshore breeze destructively interfering with the velocity of sound (about 340m/s). Reduction in speed of the sound thus means the sound will take longer to reach you and therefore the rate at which the sound wave loses energy increases, it is quieter. (if the breeze is onshore at 25km/h (about 7m/s), this will constructively interfere with the speed of sound and make it about 347m/s).
Temperature also affects the speed of sound. If the air temperature is hotter, the average kinetic energy of particles in the air increases, and thus the speed at which the sound wave reaches you increases, therefore the sound is louder as the energy of the sound wave is not used up as much.
Tops article again thanks Craig. On a realted topic .. how's the way that . . on a still early morning surf, even about 1km out to sea, you can smell someone cooking bacon and eggs like standing at the BBQ with them. Something to do with the way smell travels over water
Oh, the one to beat that is the burnt toast! Every single morning out Manly at least someone burns the toast, haha. Cheers boater.
These surf-science articles are unreal, keep up the good work guys
As a somewhat frequent lurker of this website, I'd like to give my whole support to the recent flow of scientifically based articles written by Craig Brokeback and Chris Buttcocks!
(I only use sarcasm for people I like)
Every day, whenever I open my fbook feed, I see a lot of articles on varying topics. Sure, some of it is the product of giving retards a 'share' button.
The majority of links I read are 'simplified scientific articles'. It can be interesting new developments, new discoveries or social interactions, or in this case an astute synopsis of physics relatible to many ocean dwellers all over the world.
As much as I hate to increase surfer numbers and knowledge base, you swellnet guys have a niche to make some clickbait money
I write this because there's a 3m @16 sec swell roaring now its energy is dominating my being , 2am there's very little wind & craigs article happening cos its just over a hundred mtr away is waves below the cliffs . Im a virtual buoy measuring the sound but not all times sometimes its quiet but . If you didn't like this then you wouldn't want to live here on this desolate hill otherwise. Craig must have seen the forecast& had flashbacks to camping at granites im thinking .
One swell at g.land 1-5-97 was 12ft perfect swell & it was silent ! Unbelievable when you seen it the morning .no maps so didn't even know ! I rubbed my eyes & yeah such a good swell , the same day the waves in pc vicco were on the all time epic , mag covers & stories yep same swell . Silent with the biggest lines. Fuck it's booming now tho
Camlift is that you..? :p
No its not up
I remember yorkes in the seventies and eighties you would hear the waves cracking on the beach at night and it would be tiny if not flat in the morning. Interesting article.
Haha, too right Cam, and winkie, yes, Pondie was the major one that always got me.
What about the fact that when you shut your eyes your ears become more sensitive ?
This might just be a pubescent thing though ;-) !?!
Cryptic . Tonite sounds decent 2m @14 . Sleep is possible .
Not cryptic camel . Ties in with an old joke .
ie : What's the most sensitive part of a 13 year old males body . ?.........
His ears .
I still don't get it . Sounds wierd .
It's a reference to not wanting to get caught wanking Caml.
Hah! I was waiting for someone to spell it out
Roger that I suspected something sinister.
Hey the oceans gone flat . Minor rumble certainly I will ponder why the surfs always louder at night
0.75@11 sec on the shore here southern ocean
Usually put the head torch on, go for a mid morning piss and check the surf.
Then you actually realise;)
Jeez it's been loud the last few nights! Combo of the temp inversion and a solid long period swell. Keep getting woken up during the night!
The lunar cycle is in a strong phase , hope you are getting a bit of sleep ben
Lunar cycle kept me up last night caml. Midnight and I'm thinking I'm wide awake. Fark it, I'll have a hot milo (noted sleep inducer) and read a book. Tennis was on in the background and when that finished watched Rage. Damn it was good, classic Australian tunes from the 70's and 80's.
Then that finished. Windows were open and the sound of crashing waves coming through every now and then. Must have been sizable, doesn't break hard down at the cliffs unless it's well over 4'.
In bed by 3.20 or so, up at 8.00 and off to work.
No point going to bed when the moon is keeping you up. Thankfully on the second of three very good books, so no problems.
Thatts right batfink full moon , but when theres swell its a bonus feature for insomnia . Not much noise going on here but on bens coast there is eh ?
Interested in your comment that it is 'in a strong phase' caml. In what sense?
I am very aware of the lunar influence and much affected by it, a genuine lunatic in fact. I found this one particularly strong, but only in its effect on me. How did you mean it?
Interesting read on a related topic - thunderstorms.
http://www.srh.noaa.gov/jetstream/lightning/thunder.html
This happened last night in Sydney. Around 4am the thunder bang was crazy loud, like a bomb!
Last night sounded and felt like it was fifteen to twenty feet. I'm a distance back from the waterline ('bout a kay) but the house was reverberating with each set wave. Yet the buoy data from my local was concurrently under a metre, with peak swell periods of just 11 seconds. Amazing!
Ben what were the wind conditions during this time ?
Very little.
At some places, I think it is noisiest when there is a small swell that gets close to shore before it breaks with a little slap. Somehow, that becomes this epic rumble thru the bedroom window 1/2 a km away.
No doubt it varies with location, but the especially epic night time rumble that gets you excited is often actually telling you it's small and probably not very surfboard-worthy.
That was always my understanding (before I looked further into it) - and I definitely think that's the case a lot of the time.
Surfers camp at Pondi (at Yorkes) was where I first experienced this issue and there's always some degree of this happening, no matter the size - small or solid - the stretch of beach from the surf break to the fisho shacks has long lines of smaller closeouts, which crack across the sand.
But yesterday was 4-5ft+ on the Tweed, so midnight (when it was loud and rumbly) would have still been 3ft+ (the swell had dropped) - so not quite tiny shorey slappers. Though, the coast is heavily guttered at the moment so perhaps I was hearing the inside waves on the shore.
Add in the immeasurable factor of 'anticipation'. The froth factor.
Ok, I would suggest wind noise will have a big impact and its direction. As a suggested , wave size breaking on the shore (hence smaller) I would imagine to be louder. This is a great bit of science here.
Often the overnight sound of even small waves is very loud at my house.
Up at 4:45am this morning, and it was deathtly quiet... all the more eerie knowing there was a new building (relatively) long period easterly swell in the water.
Saltwater crew danced & sounded waves & Forecast with Wave sound in caves.
Tugun means sound of waves & Cooran waves(TOS) Sounded warning for Brisbane.
1900' Burleigh Barrelometer forecast Rain for town or Sun around.
Ultra Sonic waves now thoroughly cleanse today's largest swim lagoons.
Wave pool pipes could be sounded by Pro Surfers beat, shaping live concerto waves.
Would mega o/n Concert Soundwaves overpower smallish WSR waves?
tbb salutes fellow swellnetonian WSR head honcho AndyM for keeping the Peace.
http://www.mygc.com.au/sanity-has-prevailed-coolangatta-locals-praise-sa...
Note: Coolangatta beach recently had all vegetated dunes bulldozed for CG Volleyball.
Mayor keeps pushing licensed beach privatisation to carve up WSR for whiteshoes.
Shut venues for GCCC owned Surfers Paradise,Broadbeach,B'Hds,Broadwater gigs
GCCC have shares in all that surrounds & now swing grubby mates in on ticket scam.
GCCC licensed "Opera on the Beach" at Cooly & now "Sand Tunes" $ Top Dollar Gigs
As with GCCC beach bars, block access to Pacific Ocean with fencing & bouncers.
Ambulance,Fire Services,Life Guard access is also blocked by Pub perimeter.
Pub block Beach steps as Ambos scale rocks to access Life Guard Spinal Patient/s.
Sound from the stage drowns out Shark Alarms stranding tbb & crew..
Movie Sets invite Boats,Jet Skis Boards,Drones into Beach Flags moving out locals.
2018-19 Beach Xcert cancellations due to environmental / sound / concerns.
Huntington x 2,Long Beach,Montrose,Sandy Hook,Florida,Vernon,Ontario, Cronulla,
Mosman Beach with just as many closing towns for Artists pulling out of beach gigs.
Cooly SandTunes gold tickets egged on 1,000's willing to trawl surf for entry.
WSR wasn't designed as a Pub for 35,000 nor do Dolphins/Whales have ear muffs.
Sure! Life Guards fish out sober Schoolies but this is way beyond tour of duty.
Besides! Alcohol is strictly prohibited from Qld Foreshores & Beaches.
Every WSL - Corona Shack forever dampens your right to hear evening Wave songs.
Say no to Grog & Pubs on beaches ...Respect Life Guards & your beach or lose it!
In the wash Up!
Traders are ever so happy to regain control of their town!
Sand Tunes will go ahead at stadium with All ages Access & heaps cheaper tickets!
The stadium may even dump a sandy beach & Palms to keep on song...Win! Win!
Swellnet crew thanks Andy M for protecting WSR...Wave sound is for all & always!
This is a rare but huge win for Surfing! Very good news for we Surf Critters Whole!
Wave of the Day ~~~~^~~~/(`~~~/(C`...[AndyM )
Tweed Coast is roaring tonight, though the swell is under a metre at 8 sec.
Hey Craig (and Ben Matson and Steve Shearer etc). I'm a long time swellnet subscriber - primarily for the detailed forecaster notes, but also for the interesting science and community discussion forums you keep a handle on.
I'm keen to learn a bit more about 1) how did you guys get so good at forecasting, and 2) could you recommend any introductory books for weather enthusiasts? thanks in advance!