How currents pushed debris from the missing Malaysian Air flight across the Indian Ocean to Réunion

What seems to be debris from the Malaysian Air flight MH370 that mysteriously vanished in March 2014 has washed up on on the island of Réunion in the western Indian Ocean. Investigators from Boeing are still figuring out whether the flaperon (the technical name for the piece of airplane wing) is from the missing plane, but it seems very likely that it is.

Réunion is practically on the the other side of the Indian basin from where investigators think the missing airplane may have gone down. So how did this chunk of airplane get all the way over there? Short answer: it was pushed by currents, winds and waves. From my physical oceanography perspective, I am going to discuss here what scientists and investigators thought the ocean would do to debris from a possible wreck, what the ocean actually did and what happened to the debris along the way.

What we thought the ocean would do.

Numerical models, also known as electronic oceans inside your computer, are used to predict where currents, winds and waves will push marine debris. In this case, a model run by Charitha Pattiaratchi from the University of Western Australia  was used to estimate the trajectories of crash debris as they were spread out by ocean currents and to figure out where they will end up. And that giant squiggle of red debris trajectories located just east of Madagascar are positioned right on top of Réunion! Of course, this is just a prediction and the timing is a little off since it’s only been 18 months since the crash. This mismatch probably occurred because the model was likely run with historical surface current data and idealized numerical debris, although I couldn’t find any details on the model itself (if anyone knows please send me a link in the comments!). And even though I think Prof. Pattiaratchi oversells his model by saying it “exactly predicted where the debris would go” (if it’s so accurate why hasn’t any debris been found on Australian and Tasmanian beaches?), there are enough realizations to show that debris from the crash would have likely ended up on the tiny isolated bump in the big blue sea called Réunion. So in some ways it’s not surprising that the flaperon washed up there and it’s also likely that more debris will too.

UPDATE: Another model!

And this one shows that the flaperon found on Réunion most likely came from the northern region of the search area. Hydrodynamic experts Maarten van Ormondt and Fedor Baart from Deltares used surface currents from the HYCOM model to track where marine debris might have been carried by currents in the 14 months since the crash. Particles released really far south never made it to Réunion in a year, while those released farther north did! This model more accurately tracks marine debris than the previous model because it incorporates real oceanographic data since March 2014 to estimate realistic surface currents, rather than making a prediction using historical data. That being said, predictive models are still really important! They help dictate where investigators should have searched before the debris were found, as was the case until last week.

 

What the ocean actually did.

Every news outlet seems to love posting the latest images from earth.nullschool.net to show the currents in the Indian Ocean. Why not? I love that site and the graphics are pretty! But the problem is it only shows a snapshot of the latest 5 days and is not at all indicative of the mean flow that pushed the debris across the Indian Ocean. To do that, we need to look at the average currents since the plane disappeared to get a better grasp on exactly what pushed debris to Réunion.

The most obvious feature in the graphic above are all the arrows pointing westward just south of the equator around 10-15° S. It’s called the South Equatorial Current (we oceanographers are very creative in our naming schemes). Debris from the aircraft got caught up in this flowing water and were likely pushed across the Indian Ocean smack dab onto Réunion.

But it’s a little more unclear in this image how the debris got north from the search area into the South Equatorial Current. The culprit? The West Australian Current that flows northward along Western Australia. You can’t see it too clearly here, because there is a lot of small scale eddies that mess with the averages. But if you look at a even longer term averages, it’s there. The debris probably just took a very squiggley northward path until it reached the South Equatorial Current.

Both the South Equatorial Current and the West Australian current are part of the larger Indian Ocean gyre, a giant rotating vortex of water in the southern Indian Ocean. Some of the debris, if they manage to float that long, may even end up back on the Australian coast because of the gyre!

I should also note that the debris was found about 4400 km away from where the plane might have gone down and it’s been about 505 days since the plane disappeared. Making a rough calculation with my TI-85, that means the drift speed of the debris needs to be about 0.1 m/s or ~5 miles a day to get to Réunion from the search area. That’s pretty close to the current speeds in the plot above so it’s totally plausible that this debris is from the crash.

What happened to the debris as it drifted.

Anything that has been in the ocean for more than a year will have some sort of sea life clinging to it, and this piece of wing is no exception. Look at all those gooseneck barnacles! Resident DSN barnacle expert Miriam Goldstein has informed me that this amount of barnacles could easily grow on the flaperon in the 16 months it has probably been out at sea. I’m actually a little surprised more hasn’t grown on it. She also notes that they are from the Genus Lepas, although she can’t identify the species from the photo. The barnacles don’t seem to preferentially growing on one side, which also leads me think that this piece of debris was mostly submerged while drifting.

WHAT NOW?

The search for answers regarding the plane’s disappearance has been a long and difficult one. More debris from the wreck could end up on Réunion or at least near it in the future, if it has not already. Even though we found pieces of the plane, we can’t pinpoint exactly where the plane went down as suggested by some media outlets. But there might be clues in the debris itself to at least indicate what caused the plane to veer so very far off course and disappear. My hope is if investigators can find more debris, they can figure out what happened to MH370 in the first place and finally give the families of those onboard the tragic flight can find some answers and peace.

 

ADDITIONAL RESOURCES:

The map above was made using ESR’s OSCAR data product, which combines sea satellite data (altimetry, winds, sea surface temperature) and in situ observations (NOAA drifters, moorings) to create global maps of ocean currents every 5 days. http://podaac.jpl.nasa.gov/dataset/OSCAR_L4_OC_third-deg

Here is a good summary of MH370 take-off, disappearance and subsequent searches: http://www.cnn.com/2015/07/30/asia/mh370-maps-of-takeoff-disappearance-search/