Category: ru29 (Page 6 of 22)

Since the waypoint change last week, Challengers slowed down quite a bit as the currents have now shifted to the North, despite both models consistently showing more of a westward flux.

Looking ahead, as we continue to maintain our position between the orange line (direct route from Ubatuba to Cape Town) and the red line (angled path bringing 29 towards Tristan da Cunha ) there is an interesting system lying a few hundred kilometers to our east.

The Depth Average currents for RTOFS August 14

In the RTOFS forecast above, there appears to be a large cold core eddy spinning in the clockwise direction, while below in the copernicus forecast, there are two warm core eddies rotating in the counter-clockwise direction; both resulting in a westward flux.  As both models use similar baseline readings to then derive their forecasts from, it is very interesting to see the two different reasonings behind the same westward current, and so over the next few weeks as 29 makes her way in that direction, we will keep an eye out on the data to see the evidence in our data for which forecast will get this right.

The Depth Average Current forecast for the Copernicus Model August 14

In the meantime as we make our way towards this test area, Challenger has to snake her way through the seamounts immediately ahead of us.  With the current to the north of the seamounts being due west, we have decided to duck down to the south through the valley before cutting back to the east where the current look to be more favorable.

Global Bathymetry Product for the South Atlantic Region

Force Wind Sea & Honor

Since the way point change earlier this week, Challenger has been making excellent time.  As seen in the forecasted currents from both Copernicus and RTOFS for today, 29 has made it to the south easterly jet between the eddies to either side.

Copernicus Averaged Currents Forecast for August 06, 2015

RTOFS Averaged Currents Forecast for August 06, 2015

By managing to catch this jet, we are seeing some of the best speeds of the mission as we have averaged 18 km/surfacing since the waypoint change resulting in just under 30km/day!

RU29 Velocity Plot

In the next day or so, the way point will be adjusted again to account for reaching the end of the jet as we then continue to make our way from eddy to eddy on our way to the east.

Force, Wind, Sea & Honor

This past weekend Challenger crossed the 1000 km milestone on the trans-atlantic crossing from Brazil to South Africa.

RU 29 has completed the first 1000 km of the mission

Now at 1041 km into the mission, 29 is now roughly 1/6 along the projected path passing by Tristan de Cunha to Cape Town.

RU29 Crossing the South Atlantic

Looking to the forecasted currents, the two models are both showing that Challenger is flying down the eastern side of a cold core eddy which combined with the new way point from Friday has led to an extra ~3km per surfacing.  Despite the increased distance, Challenger is continuing to show a slight overall flux to the north through its calculation of depth average currents.

Copernicus Averaged Currents August 03

RTOFS Averaged Currents August 03

Moving at this pace, we will continue to have Challenger pursue the current way point for another 2-3 days before we move the way point back east to account for the edge of the eddy we are currently taking advantage of

Force, Wind, Sea & Honor

As we head into the weekend, there is a new way point waiting to be picked up by Challenger the next time she calls in.  In preparation for the next surfacing, we have moved the way point to 30˚ South, 32˚ West in an attempt to catch the southerly current shown in both the Copernicus and RTOFS forecast models as seen below:

Copernicus Averaged Currents July 31, 2015

RTOFS Averaged Currents July 31 2015

This current should propel us to the south east over the next few days during which we hope to get a good idea on if the forecasted current are matching the gliders flight path so we can use the information to make the next way point move early on next week.

Antonio has also provided us with the salinity fields from the Copernicus forecast this week which gives us an ever better picture of the eddy field 29 is on the cusp of entering

Copernicus Salinity field forecast for 540m depth

There are two things that are really cool about the eddy field we are entering, the first being that from here on out the eddies we are encountering are part of the influx into the Atlantic from the indian ocean (see below) and the second is that the cold eddy to the south has remained relatively stationary over the seamounts in that region, similar to the cabo frio eddy along the coast of Brazil that Challenger encountered on the Ascension – Brazil trek.

Copernicus Sea Surface Height Forecast July 31

Force Wind Sea & Honor

Through the weekend Challenger continued to make good time as she flies to the south east with the distant shores of Cape Town in her sights.

As we start off the week, the discussion turns to picking the next waypoint.  The path we want to stick to falls along the orange line shown in the image above, stepping down the eddies that span the South Atlantic in a pattern very close to the pattern of 1˚ to the South, 3˚ to the East.

Copernicus Averaged Currents July 20, 2015

Looking to the Copernicus forecasted currents, we will have another few days or so of the currents pushing to the North until we will start to find the currents Challenger will be able to ride off to the east as she snakes through the eddies.

Force Wind Sea & Honor

Today we have one of those rare occurrences where not only do the models match up quite well, but in a pretty favorable fashion.  Both forecasts seen below (RTOFS in green in the first image and Copernicus in yellow in the second)  show a warm eddy and cold eddy combination about 300km to our south east that will be aiming for over the next week.  They also agree that if we keep our heading a bit to the south along our approach we should find more favorable currents along the way.  With our current waypoint, Challenger should progress somewhat along the white line shown in the images if the forecasts hold true.

RTOFS Currents for July 16. Average of 300, 600, 1000m

Copernicus Currents for July 16. Average of 300, 600, 1000m

Tomorrow morning after our pre weekend discussion we will set a new way point further out to the south east to pursue through the weekend as we try and hit the sweet spot between those two eddies.

Force Wind Sea & Honor

RU29 flew straight east over Friday and Saturday until it passed north of the seamount.  With the strong northward currents, much of RU29’s flight has been eastward so far. Early Sunday morning the waypoint was changed back to Southeast, based on the depth average currents plots from the U.S. and European models. We are currently heading in the direction shown by the orange line. And we again are in international waters.  The yellow lines mark the EEZ limit for Brazil.  Hopefully the next EEZ we enter is South Africa’s.

Zooming out to the long view, below is the South Atlantic Basin.  RU29’s trip around the basin is divided into 3 legs. Leg 1 (blue) was from Cape Town, South Africa to Ascension Island in 2013.  Leg 2 (green) was Ascension to Ubatuba, Brazil in 2014.  Leg 3 (red) is one potential flightpath back to Cape Town via Tristan da Cunha. We’ll keep this red line up as a reference.  We are currently flying along the orange line.  Total great circle  distance to Cape Town from the present location is 5,600 km.  Assuming a strong speed of 25 km/day, its about 7.5 months to cover this distance. Again assuming all goes well, that gets us to Cape Town about March 2016 at the earliest.  We are leaving tropical Brazil during the southern hemisphere winter.  As we fly southeast, we will transition into southern hemisphere summer, hopefully arriving Cape Town as their summer is ending.

Now two weeks into our mission, the team has been looking forward to which path we will take in the coming months on 29s trek to South Africa.  Our dear friend Antonio laid out four possible paths we can take:

Each of the paths stretch between 5500 and 6000km which will last around 245-280 days. The differences in the path options appear during the first 1/2 of the mission upon reaching Tristan de Cunah.  This mission will be the longest of 29’s so far and the small secluded UK archipelago is the only port available to us along the way.

Later, after crossing to the north of the EEZ of Tristan de Cunha, the paths merge as piloting shifts to jumping from eddy to eddy as they pass around the Cape of Good Hope, leading Challenger back to Cape Town.

Antonio also provided us with some nice 3D imagery of the bathymetry.  Featured in the image above, is a region of sea mounts and volcanos that are jutting up from the seabed. Going forward, we plan to pass to the north of the mountains just ahead of us before snaking our way to the south.

Looking to the forecasted currents, we have an interesting conflict to our south east.  In the image below, black vectors represent the copernicus currents at 300m while the white currents are RTOFS. 

Both forecasts show an eddy signature to the south east, however copernicus defines it as a clockwise cold core eddy while RTOFS shows it as a counterclockwise warm core eddy.

Both forecasts however show a prominent southern current a head which we plan on catching over the next few days.

Force Wind Sea &  Honor

Compare today’s currents (below) with those in yesterday’s blog entry.

Yesterday we had currents to the north for a few hundred kilometers, followed by a longer region of currents to the south.  Today we have the opposite.

We’ll need to look closer at our forecast tools.

RU29 has a cluster of seamounts due east of it.  Over the weekend we tried to pass to the south, but our trajectory says no.  Strong currents to the north prevented us from heading on a southeast track. We checked the current forecasts for an alternative plan.

Below is the RTOFS forecast for today.  Strong currents to the north for the next few hundred kilometers.  Followed by strong currents to the south.

We are planning to change the waypoint to due east.  Combined with the current to the north, the glider trajectory will be northeast, and we will pass north of the seamount cluster.  We’ll then continue into the southward flowing currents, and let the ocean take us back south.