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As we leave the home base of our sampling scheme for the last time, we have thrown the way point out to the north west.  As we get closer to shore, there is a danger of being swept to the south by the Brazil current shown in the figure below:

We have also heard that this current meanders quite a bit, so depending on where we catch it, the strength of the southward flux may vary.

MyOcean’s forecast today has a pretty cool looking eddy field within our vicinity. In the upper layers, there are two well defined eddies to our east and to the north west that can be seen through 300m.  Below that, the eddy to the east fizzles out while the one to the north west weakens with depth.  In the RTOFS model, the main feature of interest is the eddy to our West-Northwest that lies within the path we plan on flying towards the coast.  Depending on how fast this eddy moves we may be able to dissect it in the coming weeks.

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Last night Challenger completed another mile stone as she crossed the Tropic of Cancer for the second time since being deployed- however she quickly jumped back to the north as she followed the path of our final wing of the eddy sampling mission.

Over the next few days she will fly in towards the center of the fan for the last time before we throw the waypoint towards the shores of Brazil and begin making our final plans for recovery.

Looking above at the gallery for the currents today, there is a drastic contrast between what the models are forecasting.  MyOcean is showing an overall flux westward throughout the entire water column that aligns well with the deep eddy that has been moving steadily to the north.  On the other hand, RTOFS is showing an overall flux through all layers to the south east caused by the lower left rim of the warm core eddy at the base of our sampling scheme as it meets up with another eddy to our north- possibly the same eddy present in the MyOcean model.

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As Antonio criticizes my flying by saying “my three year old nephew can draw straighter lines than that!!!”  Challenger pushes along the third wing of the windmill as we sample the eddy field within the area outside of the Brazilian Exclusive Economic Zone.

Antonio also reports that it looks like the eddy has shifted out of our range of the sampling zone as the system moves to the north.  As we make our final pass through the area, we have Ru29’s course set to fly to the north west in preparation of entering the Brazil current which should carry us to the south west along the South Brazil Bight.

Dave lately has been running numbers on our engineering parameters for this flight in comparison to the mission from Cape Town to Ascension and Silbo’s crossing from Canaries to the Caribbean as those two missions done by Slocum Gliders of similar magnitude.  On our pump, we have done close to 12,000 inflections averaging out to roughly 17 per day meaning we should have about 470 days left.  We have also had a very low number of oddities from the sensor monitoring the pump and only a few on the previous mission.  This should be a good sign as while Silbo was in flight across the North Atlantic there were a number of oddities leading up to the crippling pump failure that left the glider drifting for the latter portion of the leg that ended upon recovery in Barbados in August 2013.

Looking ahead, this will most likely be our last wing of the windmill as we will begin heading in towards shore for our recovery.  The plan at this point is that a team will head down to Brazil May 12-22 to our Brazilian partners in the recovery. Being that we have just a month and a half before that window and that we would rather be safe than sorry, the feeling at base is that we are better off arriving with some time to spare and loitering off shore.

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Upon Scott’s arrival from his visit with the University of Sao Paulo in Brazil, we were given the location that the final recovery operation will take place in: Ubatuba (designated by the house symbol on the map above).  The University has a field station there where after the recovery, the team will return there to work on the glider before redeploying within a short window of time.

Challenger continues to kill time outside of Brazil’s exclusive economic zone (EEZ) as we finish the outbound portion of the second wing of the fan-sampling scheme. We will continue to fly a pattern like this for 2-3 more wings (averaging roughly 10 days per wing) as we await pending details on our recovery.

As for the currents, MyOcean continues to show the eddy most prominent at surface with lower layers continuing to flow westward.  There are also a number of eddies to the east of our sampling area. RTOFS shows evidence of the currents curling but not until 900m do we see the fully rotating eddy signature while there is one massive eddy signature now over the home base portion of the sampling area.  RTOFS also shows a beautiful full water column eddy sitting right at the center of our sampling region.

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It was an exciting week here at the Institute of Marine and Coastal Sciences because Sylvia Earle came to visit us to show support and help us celebrate our 10th Anniversary. Check out the write up on Sylvia’s Mission Blue page here.

As we begin to close the first wing, we have made some alterations to our planned sampling schematic:

Instead of flying the wind mill pattern as we had previously planned, we are now going to fly a fan pattern- going out and back to the starting point through the region of the eddy to our west.  This we feel is a safer pattern as we won’t move ourselves any further away from Brazil than we have gone previously.

Antonio also pointed out that if we look at the time series plots of the mission, over the past couple days, at depth there is a signal showing warmer water at depth- could this be a sign of the eddies?

Looking at the break down of the currents, MyOcean now only has the eddy to our west well defined at the surface while at depth it becomes a general flux to the east. RTOFS however now has the two eddies to either side of us (east and west) well defined throughout the entire water column

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Now with just 700 km between RU29 and the shores of Rio, and with more than 2 months until there’s even a hint of a chance for a recovery, we have sent Challenger on an eddy hunting mission.

As we mentioned previously, Antonio made a fascinating discovery of strong subsurface eddies reaching velocities of up to <30cm/s!  Upon further inspection we found that there were actually a number of different eddy signatures in the area and so we set out to create a sampling strategy.

Over the coming weeks, we will take RU29 and fly the windmill sampling pattern through the area in order to take a look at the structure of the water column and see if the gliders calculation of currents supports or denies the claims made by the forecast models.

Looking to the forecasted currents in our area, both models are showing eddies that appear at depth that do not hold their formation all of the way up to the surface.  In MyOcean, there is the well defined eddy that sparked our sampling scheme to our east but also a smaller eddy to the west that is visible below 600m.  In RTOFS, there are two features of interest, the one eddy close by to the east that spans the entire water column being inspected, and to the west an eddy who we begin to see around 600m and starts to take shape by 900m.

Finally, yesterday at Oceanology International, Iridium announced their Sponsorship of the Challenger Mission, through which they will provide communication services to the Challenger fleet as the mission gets rolling. Read the official press release here

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As we strive closer towards the shores of Sao Paulo, the team has been bouncing ideas around on how we can kill time.  This mission thus far has gone incredibly smoothly as we have been flying at speeds upwards of 30 km/day with just the deep current adding some minor resistance to our flight.

The most promising proposition so far has come from Antonio who has proposed that we fly the windmill pattern- hoping that the third time is the charm for this sampling strategy.  We have attempted this sampling pattern in the past, the first being with Silbo in spring of 2012 off of Madiera which failed due to user error when I mis-typed the way point.

The second attempt then met its doom as we sampled the lea of Ascension Island, where the voltage of the batteries suffered a sudden drop and the glider needed to be recovered immediately.

Now, Antonio has made a very interesting discovery looking at the myocean model: conflicting eddy fields from the surface to inflection depth!

What we propose we do now, is that we take the windmill pattern we have attempted in the past and traverse the region, inspecting this unusual event.

We also have some time on our hands as we are still awaiting our recovery equipment to ship from Ascension Island to Rutgers so we can then secure a recovery date which we hope will occur some time in May.  Also looking to the battery plots, Dave estimates we have roughly 200 days remaining.

Where we stand now, MyOcean is showing a very well defined eddy field ahead of us with our present position being on the right side of a clockwise rotating cold eddy with another cold eddy due south and a warm eddy to the south west. RTOFS meanwhile shows two pretty well formed cold eddies to our south and south west.

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As you can see from our 3D model we are in an area with quite a few seamounts. These seamounts are all still in the area of the Trindade seachannel. We will cautiously be “threading the needle” to avoid any collisions with these seamounts.

What is interesting in the current forecast today is looking at how the currents interact with the sea mounts.  MyOcean shows from surface to 900m there is an eddy circling counter-clockwise around the large seamount to our west, resulting in a full water column flux to the north.  RTOFS on the other hand has the currents in the first few hundred meters of water flowing south while at depth there is an eddy spinning in the same direction as what MyOcean shows.  Both models however agree very nicely with the presence of a nice eddy sitting in the lea of the seamount a little further to the south west.

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This week we found ourselves within 50km of the EEZ of Trindade. Trindade is an archipelago located in the Southern Atlantic Ocean. It has a population of 32 consisting entirely of Brazilian Navy personnel. The island is of volcanic origin and consists of very rugged terrain. Part of our agreements for the Challenger mission have us avoiding entering EEZ’s in which we have no contacts. So we will cautiously be flying near Trindade but will be certain to avoid seamounts and entering their EEZ.

Currents in the surface layers both show an eddy to our immediate south west. MyOcean however shows it as a counter-clockwise warm eddy while RTOFS is showing it as a clockwise cold eddy. At depth the models continue to disagree as remnants of both eddies can be seen throughout the water column.  As we get deeper this develops into a large flux north seen in the MyOcean data (which agrees with the glider’s calculations) and a southward flux from RTOFS.

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Today the currents around 29 as forecasted by the RTFOS and MyOcean models is quite peculiar.

Aside from the currents being nearly the opposite direction of each other between the two models, both show 29 in the center of an eddy solar system.  A cool feature from the myocean model is that at the surface, to our south west there is a nice tight warm core eddy that while we go down in depth, the eddy structure looks like it slants north east in our direction leaving us at the edge of the eastern side of the eddy with its northward flow that almost matches with our depth average current calculation.

The RTOFS model also shows us in an eddy field, but  only has the currents around 300 m flowing in a direction that correlates with the currents recorded by 29.  Above that at the surface the model shows a flow to the west while from 600 to 900m the current is moving largely to the south

In other news, Fabien Cousteau has agreed to help spread the word of the Challenger Mission, for which he will make a promotional video that we will air at the Catch the Next Wave conference on March 10th to kick off Oceanology International 2014!

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