Lombok waves visible from space

Craig Brokensha
Swellnet Analysis

Lombok Strait, between Bali and Lombok, experiences some of the strongest tidal flows on earth, a result of it being one of the main Indonesian throughflows between the Indian Ocean and Pacific Ocean.

Water transport through the Strait is seasonal, affected by the difference in atmospheric pressure across the ocean basins, which is driven by the monsoon.

During the south-east monsoon (our winter), sea levels are lower on the Indonesian side and the flow is from north to south. This reverses during the north-west (summer) moonsoon, but the average flow is to the south.

Amplifying the currents through the Strait and between Lombok and Nusa Penida is an underwater sill sitting at a relatively shallow 200m, with the ocean plummeting down to 4000m to the south, while to the north ocean depths drop to 1000m.

Being one of the only access points between the Indian and Pacific Oceans the ocean dynamics and currents through Lombok Strait are some of the most complex and fastest in the world.

Ocean transport rates of between 2-4,000,000 cubic metres per second - yes, per second! - are recorded through Lombok Strait, and this along with the extreme water depths have helped prevent animal species crossing between Asia and Australia. This fauna boundary is known as The Wallice Line and runs right through Lombok Strait, east of Borneo and south of the Phillipines.

With varying water densities and current speeds between the surface water and water flowing over the sill, large internal distrubances (waves) are created which are visible from space. This is relatable to disturbances seen when water floods or spills over a weir.

image11052016_250m.jpg

These internal waves travel both north and south of Lombok Strait depending on the throughflow direction with reports of them breaking and capping at times from people making the crossing to Lombok from Bali.

A satellite image taken at the start of November reveals these internal waves propagating north from Lombok Strait, visible due to sunglint: a phenomena where the ocean is so still and glassy that sun reflects off it, straight back at the observing satellite making it almost mirror like.

This has helped identify the strong internal waves which can have wavelengths up to several kilometres.

Image courtesy of Jeff Schmaltz / NASA

Comments

yocal's picture
yocal's picture
yocal commented Thursday, 15 Dec 2016 at 12:36pm

Do they break in a peeling right & left peak around Kangean?

Go deeper Taylor, go deeper!

Craig's picture
Craig's picture
Craig commented Thursday, 15 Dec 2016 at 12:41pm

Not in a surfable way. It'd be more like a surging effect. The breaking I've heard about has been in the middle of Lombok Straight, like a standing wave with opposing currents. Crazy.

Cookie1's picture
Cookie1's picture
Cookie1 commented Thursday, 15 Dec 2016 at 12:45pm

I an see some synergy between the Laird Hamilton SUP foil article and this one. I can just see that crazy bugger paddling out there now to ride some swell for kilometres.

mk1's picture
mk1's picture
mk1 commented Thursday, 15 Dec 2016 at 1:09pm

What is the "sill" - is it like a rockshelf jutting out from one side or a shallow rock barrier from bali across to lombok?

Craig's picture
Craig's picture
Craig commented Thursday, 15 Dec 2016 at 1:13pm

Yeah, like a hump between the Bali Sea to the north and Indian Ocean to the south.

This is an ocean depth chart, and you can see the shallower yellow sill at around 200m. It's 1000m deep to the north and 4000m deep to the south.

mk1's picture
mk1's picture
mk1 commented Thursday, 15 Dec 2016 at 1:19pm

Wow, I knew water flew through that area creating "the coral triangle" but wasn't aware of the shallow section. Maybe that is why the sunfish surface around there.

Jamyardy's picture
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Jamyardy commented Thursday, 15 Dec 2016 at 1:23pm

Not much paddling required to get back out the back at Bangko Bangko, that current takes you straight out. Also the local fisherman use this current to circle between Lombok and Bali on their little boats.

stoner's picture
stoner's picture
stoner commented Thursday, 15 Dec 2016 at 1:52pm

I've seen it, while trvelling on a boat from Gili T to Serangan, a set of 3, 2-3 foot "standing" waves that were a couple of kilometres long. You could see them on the horizon gradually getting closer then the boat driver just went straight over them, we got to the "back" of the set and was smooth sailing again

Craig's picture
Craig's picture
Craig commented Thursday, 15 Dec 2016 at 1:59pm

I'd love to see this, be such a trip.

paulinoz's picture
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paulinoz commented Thursday, 15 Dec 2016 at 1:55pm

Hi Craig. A couple of times at Serangan I've seen a small 1-2ft runner wave breaking almost 90 degrees to the beach into the Straight and about 50 -70 meters out from the peak when the tide changes. It broke very similar to a tidal bore; appearing and disappearing. Would this be it?

Craig's picture
Craig's picture
Craig commented Thursday, 15 Dec 2016 at 1:59pm

Yeah sounds like it!

paulinoz's picture
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paulinoz commented Thursday, 15 Dec 2016 at 2:13pm

Well, that solves that mystery for me. Thanks.

goofyfoot's picture
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goofyfoot commented Thursday, 15 Dec 2016 at 4:47pm

4km deep to the south, that's crazy.
Nice write up Craig

gcart's picture
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gcart commented Thursday, 15 Dec 2016 at 5:08pm

That explains why it was such a tough gig when I broke my leg rope at Shipwrecks one time and my board was heading to the Phillipines in quick time . The rate negotiated with one of the local "pirates" to retrieve the board & me was worth it !

mowgli's picture
mowgli's picture
mowgli commented Thursday, 15 Dec 2016 at 5:39pm

dang. should tap that for clean energy. not sure how'd you go at timing re when to install it all.

“Life is a long lesson in humility.”

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming commented Thursday, 15 Dec 2016 at 6:35pm

Wow that's cool never knew that, have also seen those weird waves though going to Lembongan.

Blowin's picture
Blowin's picture
Blowin commented Thursday, 15 Dec 2016 at 7:46pm

That was a great article Craig.

Cheers.

Simon Hayward's picture
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Simon Hayward commented Thursday, 15 Dec 2016 at 8:34pm

Our planet is amazing

spidermonkey's picture
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spidermonkey commented Thursday, 15 Dec 2016 at 8:54pm

Something doesn't quite make sense to me, so the predominant flow is Nth-Sth..What is causing the wave propagation to the Nth. Are we looking at a deep wave or surface wave? Or is that just an image of a large Sth swell pushing through the straight. I been sailing through there plenty times, can confirm the Sth current is a powerful force.

Craig's picture
Craig's picture
Craig commented Friday, 16 Dec 2016 at 7:24am

Predominant flow yes, but it switches during the summer monsoon but not to the same intensity.

zenagain's picture
zenagain's picture
zenagain commented Thursday, 15 Dec 2016 at 8:57pm

Great article, love this sort of stuff.

If a boat was to up-anchor and drift with the current, what would the peak rate of knots be?

Watashi wa metabo oyagi desu.

blindboy's picture
blindboy's picture
blindboy commented Thursday, 15 Dec 2016 at 9:42pm

A very scary piece of water. The first time I went across to Lembongan was in an outrigger at night with a solid swell, everyone was screaming, it was nuts. That was in the days before there were any losmens.

Laurie McGinness

quokka's picture
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quokka commented Thursday, 15 Dec 2016 at 10:05pm

Back in the 90's coming back from Lombok on the Bali Hai ferry we all of a sudden stopped in the middle of nowhere. I looked out the window and the water was boiling like a whirlpool, waves breaking but no reef in sight, a couple of minutes later we were off again. I thought it really weird at the time and put it down to the currents I'd heard of. This explains it.

Jason 29's picture
Jason 29's picture
Jason 29 commented Friday, 16 Dec 2016 at 7:46am

Between nusa Penida and Lombok not lembongan

Craig's picture
Craig's picture
Craig commented Friday, 16 Dec 2016 at 8:05am

Ah yes! Whoops.

caml's picture
caml's picture
caml commented Monday, 19 Dec 2016 at 12:03pm

Predominant flow is n-s only very rare to switch methinks .(
Edited incorrect assumption)

Tobiasl's picture
Tobiasl's picture
Tobiasl commented Friday, 16 Dec 2016 at 3:18pm

Apparently a favourite passage for soviet subs because of the difficulty in effective sonar tracking, if you're into that sort of thing

Tobias

caml's picture
caml's picture
caml commented Monday, 19 Dec 2016 at 1:54pm

Tobiasl I read stories from ww2 about the straight in war time that was very interesting . In 7 yesrs I traveled java / lombok strait and never saw the current flow sth-nth once. but I heard guys say it happens at bangko2 and I have my own theory of when/why it might happen if it actually really does . Nov ?

Blowin's picture
Blowin's picture
Blowin commented Friday, 16 Dec 2016 at 7:19pm

Pumps South -North at Nusa Dua more often than not.

Maybe more tide related ?

Massive tidal influence to overcome that size water flow though....

blindboy's picture
blindboy's picture
blindboy commented Friday, 16 Dec 2016 at 11:00pm

If the flow is north to south why are the waves showing a classic diffraction pattern for south to north?

Laurie McGinness

Craig's picture
Craig's picture
Craig commented Friday, 16 Dec 2016 at 11:30pm

Winter and normal flow is north to south, but this is capturing the opposite just before summer.

zenagain's picture
zenagain's picture
zenagain commented Friday, 16 Dec 2016 at 11:40pm

I asked above but would anyone know what the peak flow would be in knots?

A mate of mine drowned there a few years ago, I'm not precisely sure where though. Just wondering how fast that current would be moving?

Watashi wa metabo oyagi desu.

goofyfoot's picture
goofyfoot's picture
goofyfoot commented Saturday, 17 Dec 2016 at 4:09pm

Jeez zen how'd that happen?

zenagain's picture
zenagain's picture
zenagain commented Saturday, 17 Dec 2016 at 5:20pm

Bout five years ago Goof.

Night swimming and alcohol are not a winning combination.

Watashi wa metabo oyagi desu.

spidermonkey's picture
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spidermonkey commented Saturday, 17 Dec 2016 at 8:09am

I've seen it around 4kts,but we always crossed at neap tides and settled weather i think it'll flow 6kts easy, in places around full moon. Obviously it varies a lot E to West and N-Sth. Frightening on the Lombok side with a strong trade and swell!

Craig's picture
Craig's picture
Craig commented Saturday, 17 Dec 2016 at 8:15am

Reports of max speeds up to 8kts here, that's rapid!

http://www.indonesianthroughflow.com/

udo's picture
udo's picture
udo commented Saturday, 17 Dec 2016 at 8:24am

Read elswhere some times can be as much as 12kts

bob_s's picture
bob_s's picture
bob_s commented Saturday, 17 Dec 2016 at 8:31am

something I read has me perplexed.

A set of waves travels at say K knots on the open sea, but the waves within that set may be doing 2xK knots, both relative to a still observer.
is that weird or what?

as Bob Dillan said "the first one now will later be last"? as somehow the last moves forward to be the first then reforms as the last in the set again.

here we go "--
If you watch such a set moving out from the wake of a boat for example you'll see something interesting. The set of waves moves. Imagine that the set of wave shown above is moving to the right. But the individual wave crests that make up the set move within the set. If you watch real waves closely you will see that a wave is born at the back side of the set, on the left, and then moves to the right twice as fast as the whole set is moving. It grows in amplitude until it reaches the middle of the above set, then it continues to the right shrinking in amplitude and disappearing at the front end of the set.

There are thus two velocities of travel associated with a deep water wave, the velocity of an individual peak, called the phase velocity, Cp, and the velocity of sets of waves called the group velocity, Cg. In theory, for deep water waves the phase velocity is exactly twice the group velocity.
http://www.exo.net/~pauld/activities/waves/waterwavespeed.html

bob_s

Craig's picture
Craig's picture
Craig commented Saturday, 17 Dec 2016 at 3:46pm

Yeah that's group velocity, while a single wave will move at half the group velocity.

It's like riders cycling in a pack and switching from the front to back to conserve energy.

When standing on a cliff looking at sets incoming from a far distance you can see this happening with waves appearing and disappearing in the set.

bob_s's picture
bob_s's picture
bob_s commented Monday, 19 Dec 2016 at 8:45am

thanks for that - I will now look out for it possibly even on webcams? I think it must be in deep water? I can visualise what I should be looking for and focusing on that it should be apparent.
- Apparently part of the nature of sets of waves is that the seventh ( or middle ) wave is always the largest. Also, it doesn't matter, what type of waves its still the same for general wave theory? Maybe the medium counts?
So the location must retain its greater energy, but the actual waveforms travel back and forth and around they go adopting the size at each location - that's crazy.

The cyclist explanation is a good one to help get one's head around it. But each location keeping its own energy "signature" - that's interesting? The riders change from front to back and conversely, but their capability for each location (energy) stays the same?
:)
wait a minute - don't the single ( individual) waves move at double the entire (set) group velocity?
Or do you mean an isolated single wave that is not part of a group?

bob_s

BeachBumEd's picture
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BeachBumEd commented Saturday, 17 Dec 2016 at 10:04pm

Very interesting article- and comments below it... I've seen these standing waves and whirlpools many a time.

This north south current is also why DP gets as good as it does. Causing the wave to slow in velocity bend or angle as it hits shallower waters and pitch further against the current...

As a marine engineer I've often imagined a massive green energy system... a connected drill pipe style - underwater impeller - power generator - set up over the ridge of the big hill at DP going down that 2-4000 m... hmmm

Maybe I'll set up a go fund me ... who's in?

caml's picture
caml's picture
caml commented Monday, 19 Dec 2016 at 1:57pm

The wallace line separates flora and fauna reaching bali and has done for eons , Nothing makes it across?
That proves that the current does not slow down or reverse because if it did then plenty of opportunity for the flora / fauna to survive a strait migration ? I believe the reverse current sth to nth might be surface current but it is deceptive because its still moving sth but the surface flow ( aided by monsoon winds) is actually pushing s-n but it isnt really . its the bottleneck part that tells the most . Every time I ever crossed straits of bali e/w the ferry always curved his path to the north side never sth ever . I am interested to hear of counter/claim discussion ?

AndyM's picture
AndyM's picture
AndyM commented Sunday, 18 Dec 2016 at 11:58am

I'm going to bust out my inner pedant (which to be honest isn't very far beneath the surface).

Unlike winds which are named by the direction they're coming from, currents and tides are described by the direction they're heading, i.e. they direction in which it's "setting" -
e.g. a current going from south to north is described as north-setting

southey's picture
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southey commented Sunday, 18 Dec 2016 at 11:26pm

Hi guys .
Apologies I've been working near 90 days straight . Still read occasionally/ briefly .
I'm with Camel on this . The North Setting " shock wave " would only be a tidal correction as the tide slackens . The flow may slacken near large incoming tides or more importantly during years of the -Negative IOD and El Niño combo .
So early this winter would have seen the closest conditions to see the near slackening .
The reasoning for the ITF is more weather driven than tidal . And ENSO is the prime atmospheric driver of this extroadinary hydrodynamical feature . Seasonal effects will also heighten flows due to the Nth Hem Summer higher water Temps in the WPWP /Sth China Sea .
Sorry if this is the wrong place , but if anyone is keen to learn more about ENSO , MJO , IOD and ITF ?
I'm hopeless at trying explain clearly , simply and concisely . So when I came across this the other week I thought it would be great for those keen in here .
It goes for a while , but is really worth it .
https://m.youtube.com/watch?v=hz2-6wwVnZs&ebc=ANyPxKoUzq4LW4d4nbvj0kg820...

" SA's Reserve Capacity "

caml's picture
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caml commented Monday, 19 Dec 2016 at 1:03am

Andym thanks for your thoughts . Yes southey I believed that the tidal ring was a phenomenon like explained in your post . Adjustment or whatever ) because that is the side of the bottleneck that has the build up of water . Im led to believe that around nov the daytime tides will lessen the tidal coefficient thus allowing the reverse south To north a component & that is superficial movement . The opposite is in may when the flow is strongest in the daytimes . Therefore the most likely time to see reverse current would be nov-dec-jan.
as far as I know

caml's picture
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caml commented Monday, 19 Dec 2016 at 1:58pm

That tide wave is at high tide and its reverbed . Craig can you tell us that info ?

Craig's picture
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Craig commented Monday, 19 Dec 2016 at 8:19am

The southerly flow doesn't just slow down, it is totally reversed through the summer monsoon.

But the net flow over the whole year is to the south, the most recent time when net flow for the whole year was north was in 1998, El Nino event.

"The seasonal variations occur due to the seasonal climate changes. During the monsoon transition periods in December and April-May the out flow is blocked by a Kelvin wave (South Java current) which moves along the coast south of Java. Mostly this causes in these periods a net northward flow.

In summary, the measurements of the through flow indicate at least 4 important time scales:

(1) a steady annual mean southward flow between the western Pacific and the Indian Ocean;
(2) a seasonal modulation of the mean flow producing maximum speeds in the months of the northern summer and minima in late fall and winter;
(3) Strong northward flow reversals occurring in January through April;
(4) a mean annual northward flow during the El Ni˜no years."

Craig's picture
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Craig commented Monday, 19 Dec 2016 at 8:21am

Great discussion though, and lots of cool observations of this internal wave!

caml's picture
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caml commented Monday, 19 Dec 2016 at 2:00pm

Craig I want to decipher you . Do you think that photo is a very rare incident or it happens often ? Where is this quote yours from ?

When the normal southward flowing current reverses the wave at bangko2 is not si good . Keen to figure out about that lesser known northward flow

Craig's picture
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Craig commented Monday, 19 Dec 2016 at 10:08am

Hi Cam, those quotes were from this article.. http://wwwhome.math.utwente.nl/~wwwtw/aamp/MScTheses/MSc_WP_Visser.pdf

If you google Indian Ocean Throughflow Internal Waves, or Lombok Strait Internal Waves there are lots of studies :)

No this happens often, not rare at all. I'd say to avoid the wave turning off you'd avoid going through late spring/summer chasing it. 

caml's picture
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caml commented Monday, 19 Dec 2016 at 11:34am

Thanks Craig , I think early sept might be the most perfect for the surf break . Early winter has stronger current perhaps a bit too strong . I may have interpreted the sat picture incorrect , and im going to recheck it . Just talked to mate who knows some stuff and he mentioned the incoming current along the nusa dua side , & the ferrys route across lombok straight . Im warming to the notion that this reversing really happens

tonybarber's picture
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tonybarber commented Monday, 19 Dec 2016 at 10:13am

Great discussion on this ... we know more but geez we know less.
It certainly is crazy ride across.

caml's picture
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caml commented Monday, 19 Dec 2016 at 12:08pm

I misinterpreted the sat pic & can see it now . Thought it was depth contours not tidal surge . So the pic was nov 4 , & I have seen it from sengigi lombok when the waves there turn on in nov/dec . Its all Adding up !

Craig's picture
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Craig commented Monday, 19 Dec 2016 at 9:53pm

Cam put these Bathy and satellite images together side by side.

caml's picture
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caml commented Tuesday, 20 Dec 2016 at 1:54am

And its true. thanks for the discussion everyone .
Where do you get more satellite pics of the straits ? Like when its flowing normal south setting ?

Craig's picture
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Craig commented Tuesday, 20 Dec 2016 at 2:01pm

And a couple more zoom images from Cam. There are more around the web I'll post a bit later.