Introduction

The Ocean Cleanup, brainchild of Dutch inventor Boyan Slat, was in the news again this past week after announcing that in addition to the fact that their system is unable to collect plastic as intended, it suffered a mechanical failure. “Wilson” is currently being towed to Hawaii, where it will undergo repairs and upgrades, presumably to be towed back out to the garbage patch for a second trial.

I am not a mechanical engineer, so I don’t intend to comment on the details of their mechanical failure. I am, however, a sea-going oceanographer. Which means that I am used to the sorts of situations with scientific research equipment that was so succinctly paraphrased by Dr. Miriam Goldstein:

Designing for physics

But beyond the engineering, there are the questions of what the *physics* are that TOC are relying on for their system to be successful. Some of you may recall that the original design was to moor (i.e. *anchor*) their device in 6000m (20000 feet) of water, and let existing ocean currents sweep garbage into the U-shaped structure. Thankfully, they realized the challenges associated with deep-ocean moorings, and abandoned that idea.

The latest design iteration (misleadingly called “System 001”, as though they haven’t built and tested any other previous to it), is to have a freely-drifting system, avoiding the use of anchors. TOC claim that under the influence of current, wind, and waves, their design will drift *faster* than the plastic — causing it to accumulate in the U, making for easy pickup. They summarize the concept with a little explainer video on their website, with a representative screen shot below:

Based on a quick Twitter rant that I had after thinking about all this for a few minutes (see here), I wanted to explain out the various points that have either a) been missed by TOC design team, or b) deliberately excluded from their rosy assessment of how they expect their system to actually collect garbage. What follows is a “first stab” at a physical oceanographic assessment of the basic idea behind “System001”, and what TOC would need to address to convince the community (i.e. scientists, conservationists, etc) that their system is actually worth the millions of dollars going into development and testing.

The premise

As outlined in the video, the premise of System001 as a garbage collection system is that through the combined action of wind, waves, and currents, the U-shaped boom will travel faster through the water than the floating plastic, thereby collecting and concentrating it for eventual removal. This appears to be based on the idea that while both the boom and the plastic will drift with the current, because the boom protrudes from the water (like a sail), it will actually move faster than the surface water by catching wind.

There are some issues with this premise. Or, at least, there are some real aspects of oceanography that have either been ignored or missed in thinking that such a system will behave in the predictable way described by TOC. I’ll try and outline them here.

Stokes drift

Any of you who may have had an introduction to ocean waves may have heard that during the passage of a wave, the water particles move in little circles (often called wave orbital motion). While not a bad “first-order” description, it turns out that for real ocean waves there is also some drift in the direction of wave propagation. This drift is named after Gabriel Stokes, who first described it mathematically in 1847 (see wikipedia article here).

The amount of drift depends nonlinearly on both the amplitude and the wavelength of the wave. For example, for a 0.5m amplitude wave with a wavelength of 10m and period of 10s (something like typical ocean swell), the drift velocity is about 10 cm/s right at the surface.

Of course, the Stokes’ solution describes the motion of the water parcels being moved by the wave. For those water parcels to then have an effect on anything in the water, one would need to consider the various components of force/impulse/momentum (i.e. our buddy Sir Isaac Newton). Needless to say, it seems obvious that a smallish piece of neutrally buoyant plastic will respond to the Stokes drift much more readily than a 600m long floating cylinder with a large mass (and therefore large inertia).

This alone could be enough to quash the idea of a passive propagating collection system. Mr Slat?

Ekman currents

While we’re talking about long-dead European fluid mechanics pioneers, any study of the effect of winds and currents wouldn’t be complete without a foray into the theories proposed by Swedish oceanographer Vagn Walfrid Ekman in 1905. What Ekman found was that when the wind blew over the surface of the ocean, the resulting current (forced by friction between the air and the water) didn’t actually move in the same direction as the wind. The reason for this is because of the so-called “Coriolis effect”, whereby objects moving on the surface of the Earth experience an “acceleration” orthogonal to their direction of motion that appears to make them follow a curved path (for those who want to go down the rabbit hole, the Coriolis acceleration is essentially a “fix” for the fact that the surface of the Earth is non-inertial reference frame, and therefore doesn’t satisfy the conditions for Newton’s laws to apply without modification).

Anyway — the consequence is that in an ideal ocean, with a steady wind blowing over the surface, the surface currents actually move at an angle of 45 degrees to the wind direction! Whether it’s to the left or right of the wind depends on which hemisphere you are in — I’ll leave it as an exercise to determine which is which. And what’s cooler, is that the surface current then acts like a frictional layer to the water just below it, causing it to move at an angle, and so on, with the effect being that the wind-forced flow actually makes a SPIRAL that gets smaller with depth. This is known as the Ekman spiral.

The actual depth that the spiral penetrates to depends on a mysterious ocean parameter called Az, which describes the vertical mixing of momentum between the layers — kind of like the friction between them. What is clear though, is that a small particle of plastic floating close to the surface and a 3m deep floating structure will likely not experience the same wind-forced current, and therefore won’t move in the same direction. Hmmm … that’s going to make it hard to pick up pieces of plastic.

What is a “Gyre” anyway?

The final point I wanted to make in this article (I have more, which I’ll summarize at the end for a possible future article), is to try and give a sense of what currents in the ocean (including in the “gyre” or in the region often referred to as the “Great Pacific Garbage Patch”) actually look like. The conception that there is a great swirling current 1000’s of km across is true only when the currents are averaged for a very long time. At any given instant, however, the ocean current field is a mess of flows at various space and time scales. An appropriate term for describing typical ocean flow fields is “turbulent”, as in an oft-viewed video made by NASA from satellite ocean current data.

To illustrate this, I took some screenshots of current conditions from the wonderful atmosphere/ocean visualization tool at earth.nullschool.net showing: ocean currents, surface waves, and wind.

These images illustrate the potential problem with TOC idea, by highlighting the fact that the wind, wave, and current fields of the ocean (including even in the “quiet” garbage patch) are highly variable spatially and temporally, and are almost never aligned at the same period in time. What’s more, is that the currents and waves at a given time and location are not always a result of the wind at that location. Eddies in the ocean are generated through all kinds of different processes, and can propagate across ocean basins before finally dissipating.

Similarly, surface waves have been measured to cross oceans (i.e. the famous “Waves across the Pacific” study pioneered by the transformative oceanographer Walter Munk).

Other issues

Following the “rule of three”, I tried to hit what I consider to be the biggest concerns with TOC system design and principle, from my perspective as a physical oceanographer. However, there are other issues that should be addressed, if the system as designed is really believed by the TOC team to be capable of doing what they say. And really, it seems like a crazy waste of time on behalf of everyone involved to have spent this much time on something if they aren’t sure it will even work theoretically … not to mention the money spent thus far. So, part of me *has* to believe that all the dozens of people involved care deeply about making something that might actually work, and they have studied and considered all the effects and potential issues I (and others) have raised.

Anyway, the other issues are:

• What is the actual response of the system to a rapid change in wind/wave direction? Wind can change direction pretty quickly, especially compared to ocean currents. What’s to prevent a bunch of accumulated plastic getting blown out the open end of the U after a 180 degree shift in wind but before the system can re-orient?
• What about wave reflection from the boom structure itself? It is a well-known fact that objects (even floating ones) can reflect and “scatter” waves (scattering is when the reflected waves have a shorter wavelength than the original ones), and it seems like this could create a wave field in the U that might actually causes drift *out* of the system.
• The idea that all wildlife can just “swim under” the skirt (because it’s impermeable) is not supported by anything that I consider to be rigorous fluid mechanics, aside from the fact that much of what actually lives in the open ocean are non-motile or “planktonic” species. There are a lot of communities in the open ocean that float and drift at the surface, and I see no way that if the System collects floating plastic as it is designed that it won’t just sweep up all those species too. The latest EIA brushed off the effect of the System on planktonic organisms by stating that they “are ubiquitous in the world’s oceans and any deaths that occur as a result of the plastic extraction process will not have any population level effects”. But that doesn’t take into account that the stated mission is to deploy 60 such systems, which are estimated to clean the garbage patch of surface material at a rate of 50% reduction every 5 years. It stands to reason that they would also clean the Pacific of its planktonic communities by the same amount.

The post The (ocean) physics of The Ocean Cleanup’s System 001 first appeared on Deep Sea News.

OMG Irma. It is going through the Caribbean and slamming everything in its path. I’ve been getting updates from friends in the Virgin Islands and it sounds like it was harrowing. Thankfully they made it through which is the most important part (even though their stuff may not have). Other islands have not been so lucky.

This is a monster hurricane, fueled by warm waters in the Atlantic. Just to get a sense of how insane it got in Barbuda, here is the atmospheric data from a water level station there. The eye of the hurricane passed right overhead, which is why you see the insane drop in air pressure.

The wind speeds got up to 100 knots before the anemometer conked out. These winds are no joke, reports indicate that nearly every building on the island suffered damage, if not completely destroyed.

Update: The anemometer was completely destroyed.

Just saw highest wind speed I've ever seen on a WX ob. Anemometer at #Barbuda blew away after recording gust to 155 mph. #Irma pic.twitter.com/aNwT5i04gf

— Dan Satterfield (@wildweatherdan) September 6, 2017

Another problem for this tiny island with wide areas of low elevation, storm surge. Preliminary data shows it got up to 8 feet.

There’s also some oceanographic data from a buoy located south of St. John in the U.S. Virgin Islands that’s part of the Caribbean Integrated Coastal Ocean Observing System (CarICOOS) . Strong winds with gusts over 60 km/h accompany the pressure drop. 

The water temperature data is intermittent, but you can definitely see seawater getting colder. Wave and wind mixing churns up cold water from the deep ocean, causing surface water temperatures to drop. 

This buoy also has salinity data, and you can also see the effect of the mixing in the increase in salinity, as deeper saltier water is mixed to the surface. There is also a drop in salinity right before the hurricane hits which could be caused by rain freshening the sea surface or just fresher water being pushed past the buoy. From this data, you can’t distinguish the two causes.

Lastly, let’s take a look at the wave data. Wave heights got up to nearly 19 feet at the peak of the storm. Some waves might have been larger as this plot shows averaged values.

Another fascinating plot is the wave direction which shows how waves emanating from the center of the hurricane. The wave are coming steadily from the East (90 degrees on the compass rose) until the eye passes overhead, at which point the wave direction turns 180 degrees completely to the West (270 degrees on the compass rose).

That was my oceanographic quick look. I’m hunting around for some ocean robot data, as NOAA AOML deploys their gliders into hurricanes, but haven’t found any yet. I’ll post when I do. For another take on the storm, take a look at my friend Jyotika’s Tropical Storm Blog.  It’s got good science and a good rundown of where Irma has been and where it’s going.

For those of you in Irma’s path, make sure you are prepared and take the necessary precautions to stay safe. Here are tips from NOAA’s Hurricane Preparedness site.

The post A quick look at the data from inside Hurricane Irma first appeared on Deep Sea News.

Using computer art magic, Armand Dijcks has turned the still photographs of Ray Collins into wonderful kinetic images of waves. Turn on full screen. Press play. Be soothed. Calm out.

The post Morning Zen: The infinite waves of Ray Collins first appeared on Deep Sea News.

#Landsat8 saw fine, bright filaments on shallow, super salty #Garabogazkol yesterday.
Bands of foam perhaps? This tweeter does not know. pic.twitter.com/ugSzIS5IGB

— NASA Ocean (@NASAOcean) April 5, 2017

This is the point in class where I raise my hand, jump up and down in my seat, and yell “ME! ME! I KNOW THE ANSWER!” Yes, the filaments contain foam. They also contain flotsam, jetsam, and all sorts of other floaty sea bits. But lines of buoyant sea stuff isn’t the only story. The lines have a greater tale to tell about about the water underneath them.

If you have two people run into each other, they hurt. If you have two surface currents run into each other, they dive. This is what is happening along each of these lines. Waters meet up, have no where to go, then get pushed downward. Unfortunately for the floaty bits, they are just too floaty to descend and accumulate at the surface where the water converges. Come to think of it, this process might also be forming the dust bunnies under my bed. But I digress….

There are all sorts of dynamic ocean processes that forces water to downwell and form these foamy filaments. Traveling waves can overtake slower water and push it downward. Rotating, wind-driven Langmuir cells can push water together in long sets of lines that are parallel to the wind. Lighter water overrides denser water at fronts between different water masses forming lines at there interface. ALL OF THIS COULD BE HAPPENING IN THIS LAGOON ADJACENT TO THE CASPIAN SEA RIGHT NOW!

But foamy streaks aren’t just for satellite imagery. You can see them in your very own local ocean or lake! Plus you get the added bonus of seeing all the other non-foam they contain like seaweed, algae, driftwood, sea ice and all the sea life clumps of floaty stuff attract. Like a college student who has maybe had one too many, go forth and streak ocean, go forth.

The post If you love geophysical fluid dynamics, then you will love these foamy streaks in a lagoon first appeared on Deep Sea News.

Although I was hoping this robotic fleet was deployed for total ocean domination, their true goal was to pretend that they were plankton. Which means they have to act like a plankton. Some plankton are able to move around a little bit, but most of the time are just pushed about by water. For these robots to mimic the movements of plankton, the trick here was to make these Lagrangian floats follow a particular patch of water that is being pushed about by currents and waves. By deploying 16 robots, then you can see how these forces create the plankton patches that have been seen in the ocean.

Which is exactly what this tiny swarm did! And, be still my physical oceanographer heart, the robotic plankton patchiness was caused by internal waves. When the group was in the wave crest, they spread apart! When the group was in the wave through, they clumped together! Exactly as an internal wave should command them.

Let’s not forget the awesome tech that made this happen. Being able to follow a water blob isn’t easy. The robot needs to continually monitor its external surroundings and adjust its buoyancy to stay at a constant depth. And tracking the position of anything underwater? You need to do it with sound. Here they used an array of five sound sources around the swarm that talked to it with special acoustical pings. But to keep the robots small, they couldn’t answer back. They just listened and recorded a sequential round of pings from the sources, which was downloaded later. The location is then determined from the difference in time between when the five pings were transmitted and when they were received. This is some elegant signal processing people.

I only have one suggestion, you hand all the robots over to me and I call them Martini’s Tini Ocean Robot Navy. I shall appear tall, they shall remain small and together we shall drift over all.

REFERENCE

Jules S. Jaffe, Peter J. S. Franks, Paul L. D. Roberts, Diba Mirza, Curt Schurgers, Ryan Kastner & Adrien Boch. A swarm of autonomous miniature underwater robot drifters for exploring submesoscale ocean dynamics.Nat. Commun., 8. 14189 (2017) doi:10.1038/ncomms14189

The post Am I a Robot or am I a Plankter? first appeared on Deep Sea News.

But if you were in a 20 m fishing boat and the wave was breaking it would look a little more like this:

In some ways, this giant wave was created by the perfect storm. A cold front passing through the North Atlantic created strong winds over 40 km/hr. In the open ocean, these winds can blow over a long distance uninterrupted. The longer the fetch length, the bigger the wave. All these features combined to make a mondo wave set.

But is it the biggest wave? Depends on what kind of wave you are talking about. On the surface of the ocean? NOPE. That was a 29 meter wave recorded by a ship in 2002. Swell breaking on shore? NOPE. Breaking waves over 30 meters (100 ft) have been seen AND surfed in Nazaré, Portugal. And lest not forget my Ph.D. pretties, internal waves? NOPE AGAIN. These waves that occur in the deep sea can easily be over 200 m tall! While this isn’t the biggest wave, it is still record breaking and impressive. I’m just glad I’m not that flailing buoy that measured it!

The post Big wave story is big first appeared on Deep Sea News.

On the second day of Christmas NASA Earth Science gave to me:
Two working jet engines,
and advance warning of Hurricane Activity.

On the third day of Christmas NASA Earth Science gave to me:
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the fourth day of Christmas NASA Earth Science gave to me:
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the fifth day of Christmas NASA Earth Science gave to me
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the sixth day of Christmas NASA Earth Science gave to me
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the seventh day of Christmas NASA Earth Science gave to me
seven seas to sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the eight day of Christmas NASA Earth Science gave to me
eight less viruses to die from,
seven seas to sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the ninth day of Christmas NASA Earth Science gave to me
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the tenth day of Christmas NASA Earth Science gave to me
ten cups of water,
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the eleventh day of Christmas NASA Earth Science gave to me
eleventh hour rescues,
ten cups of water,
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

On the twelfth day of Christmas NASA Earth Science gave to me
twelve hundred degree cooling,
eleventh hour rescues,
ten cups of water,
nine giant zucchinis,
eight less viruses to die from,
seven seas to safely sail in,
six non-toxic oysters,
five meter waves,
four weather satellites,
three prong power,
two working jet engines,
and advance warning of Hurricane Activity.

THE END.

We’ve reached the end of this song, but we have also may have reached the end of NASA Earth Science too. In case you haven’t heard, NASA Earth Science may be on the chopping block. Yeah NASA Earth Science studies change, but it also figures out how we can safely live and move about this complicated environmental system that exists on our planet. Our way of life has been ridiculously improved by pointing the science lens inward from space as well as outward. If we lose NASA earth science, we lose all the verses in this song. If these are products that make your life better and safer, then support NASA Earth Science by sharing all the good things it does for you.

Thanks! *steps off tiny soapbox*

The post The Twelve Days of Christmas – NASA Earth Science Edition first appeared on Deep Sea News.

I mean look at this awesome sequence of 3 internal waves groups you can see from space. These solitons are coming at you Palawan, breaking in UR seashores.

Solitons are a particular type of internal wave that become humongous through a series of complicated interactions. But all the action is underwater. The surface wave while incredibly wide, is less than a meter high!

Here are some smaller, yet equally impressive internal waves from my neck of the woods: Bellingham Bay, Washington. Seriously lens dust, you are blocking some truly awesome internal wave imagery.

Look at this internal wave refract and wrap its crests and troughs around Dongsha Island in the South China Sea. It’s like ocean physics is giving geology a hug. AWWWWW.

YOU GUYS. This is buy-one-get-one-free of internal waves.

Speaking of the atmosphere, did you know there are internal waves in the sky too?  OH HAI baja, make me some waves.

Winds blowing past a cluster of South Sandwich islands makes a cluster of waves. But the real question is will they make a wave sandwich?

Let’s just make cram my love of ocean, waves and ice all into one image. Atmospheric internal waves created by icebergs. I’m just going to go explode now. HAPPY EARTH DAY!

The post Some of the best internal waves for Earth Day first appeared on Deep Sea News.

I use a waterproof case on my iPhone because I live in Seattle and I constantly drop it. Ryan Pernofski has a waterproof case on his iPhone to take gorgeous slow-motion videos of waves. I think he wins in “Best use of a waterproof case” category. For more slo-mo awesomeness follow the #slowmocean hashtag on Twitter, Instagram and Vine.

H/T to Fuck Yeah Fluid Dynamics for the video link

The post #Slowmocean satisfying your need for sublime slow motion wave videos first appeared on Deep Sea News.

Check out @NWSSeattle image of windstorm! We’re monitoring the situation and will have highway updates here. pic.twitter.com/WEvmMInlKs

— WSDOT Traffic (@wsdot_traffic) March 13, 2016

We had a pretty spectacular windstorm here in Seattle yesterday, with winds up to 56 mph. Word to the wise, when attempting kite flying between downpours, go to a park not the sidewalk by your house (sorry neighbor kid I almost decapitated). But before wreaking airborne havoc on my ‘hood, I got to catch a glimpse of the awesome wave action that was caused by this storm. In case you didn’t know, Seattle is a city that is surrounded by water: Puget Sound to the west and Lake Washington to the east. And I crossed Lake Washington’s I-90 floating bridge right at the peak of the storm! Overtopping waves closed down the eastbound span, but even on the less side my car STILL got splashed with water. Unfortunately I was not able to take a video (I was driving and I’m not reckless all the time), but thankfully lots of other people did.

EVERYONE I DROVE OVER THIS BRIDGE! 

Check out waves crashing against I-90 floating bridge on Lk WA. Eastbound I-90 mainline shut down due to highwinds pic.twitter.com/uW7VEd46s6

— KOTV 6 Jussero (@JJusseroKOTV6) March 13, 2016

Here’s the view from the 520 bridge.

And then they closed it. 

1st time since 10/25/14, 520 floating bridge closed due to high winds. Could be last time w/new bridge opening soon. pic.twitter.com/bLDSHBlg0n

— WSDOT Traffic (@wsdot_traffic) March 13, 2016

BECAUSE WAVES. 

Picture of the tower on the 520/Evergreen Pt. bridge earlier this afternoon. #wawx pic.twitter.com/nPwU5DvJ0n

— NWS Seattle (@NWSSeattle) March 14, 2016

Oooooohh timelapse…OMG THE WHOLE BRIDGE IS MOVING.

https://www.youtube.com/watch?v=IByZ8VqBULE

Just going to pan over to the Hood Canal Bridge for some constructive interference of waves hitting and reflecting off the pontoons. 

Even tiny Greenlake had whitecaps.

I'm out and about in Seattle checking on windstorm. Some whitecaps and spray at Green Lake https://t.co/Bms5bCISYe pic.twitter.com/IkTSRByF0J

— Daniel Beekman (@DBeekman) March 13, 2016

You know, maybe I shouldn’t always want to get the first spot on the ferry from the San Juans. Wait for it….

But in the end, Mother Nature reminds us why we love it here :) 

Today's stormy skies and a moment of Zen here in the Emerald City pic.twitter.com/1bGyYncel8

— Tim Durkan (@timdurkan) March 13, 2016

The post Waves of Washington’s Windstorm first appeared on Deep Sea News.