Archive for the ‘Atlantic Crossing’ Category

35 kilometers

Wednesday, November 11th, 2009

Reported currents at the 7 pm surfacing were nearly due east, running 12 cm/sec.  Scarlet is doing a bit over 15 cm/sec relative to the water.  A good speed at this stage.  We'll hold the waypoint for this 7 pm to 3 am segment, and again for the 3 am to 11 am segment.  Then we'll shift the waypoint north 15 minutes and run parallel to the northeast velocity vectors in the satellite altimetry. 

Distance to the Spanish EEZ is 35 km.  Scarlet flew a total distance of 22 km in the last 24 hours.  Clicking off the segments, the friday 11 am surfacing will be one to watch.  We'll see if we can set up for the live broadcast from the COOLroom.

I'll have to figure out what to do with by 10:55 to 12:15 class.  Either the glider surfacing or the class has to be moved.   More on that decision tomorrow.



One thing we are watching more closely is the vessel traffic. We are entering the most dangerous waters of the entire journey. Students have been monitoring vessel traffic off of Spain for at least the last month.  Below is one of the worst traffic cases.  It looks like there is no place that is totally safe, and there are some yellow lines we are very worried about crossing. We will need to minimize our surface time.  Changes for every surfacing will need to be planned in advance.  We won't want to keep this glider at the surface while we make up our minds on what to do next.



44 kilometers

Wednesday, November 11th, 2009

Results from Scarlet's 11 am surfacing are shown below.  The reported ocean current is a bit of a surprise, 12 cm/s to the SE.  Its certainly not on our satellite map.  Satellites say the currents should be to the NE. We'll check what products we have from Spain. We are continuing to fly NE.  Same objective cross into Spanish waters (thin yellow arc) follow currents to NE and into the yellow eddy discussed in the morning blog.  44 kilometers to the Spanish EEZ.


Morning Update – 50 kilometers

Wednesday, November 11th, 2009

Tail current has decreased to 8 cm/sec.  Scarlet's speed relative to the water is holding steady at 17 cm/sec. Still moving along the line to the northeast, targeting the outer edge of the green circle.   If we try to stay in the green circle, we could get advected south to Lisbon.  So we'll continue moving around the outer edge of the green and into the yellow circle as best we can.  West of the yellow circle is the eddy of unknown sign, the area of high uncertainty identified in red.  East of the yellow circle is another racetrack shaped eddy that circulates through the ship lanes.  One ship every 12 minutes in the main line.  As of this morning, the yellow area is our target.

Distance to the Spanish EEZ is down to 50 km.


58 Kilometers

Tuesday, November 10th, 2009

Scarlet has found a nice tail current of about 15 cm/sec.  Her own speed was clocked at 17 cm/sec relative to the water.  Nearly 9 km made good over the last 8 hour segment.  Total distance to the EEZ is down to 58 km. We moved the waypoint north again.  We want to ride the outer edge of that loop around the green circle. 


Zooming out to the full region, we are trying to find a safe place to put Scarlet once we get inside the Spanish EEZ.  The currents in the green circle above are no longer an eddy.  The image below shows the eddy that once was there has evolved into a jet headed straight to Lisbon.  Now we instead have two eddies a bit farther north, with the offshore eddy circled in yellow.  If you follow the currents in towards the inshore eddy, your path will look something like the black line.


If you now superimpose a snapshot of the vessel traffic off Spain & Portugal, we see the black line crosses through a highly trafficed region.  The safer eddy is the one in the yellow circle.  Looks like we will try to follow the current in then stop inside the yellow eddy.


75 kilometers to Spanish waters.

Tuesday, November 10th, 2009

Drake continues to make steady progress to the east, holding the line perfectly.  A truly amazing test. We'll soon move the waypoint out farther to the east and keep going.


Zooming into Scarlet, we see she is 75 kilometers (thin white line) from the Spanish EEZ (the thin yellow arc).  The pitch adjustment made yesterday looks like it increased Scarlets forward speed to 16 cm/sec.  Thats nearly 14 km/day on her own.  Satellite altimetry says currents are also to the east.



Planning for where we send Scarlet once she enters the Spanish EEZ has become the topic of discussion. The eddy that was in the green zone has evolved into a loop in a strong jet that heads south to Lisbon - our Plan B for recovery.  The yellow zone shows an eddy that has developed inside the Spanish EEZ and is offshore of 12 W (think yellow north-south line). Thats one place we can park. Another option is to try to ride around the outer edge of the loop in the green zone, jump out and head in along the orange  line.  The worry there is the increase in ship traffic.




98 Kilometers to the Spanish EEZ

Monday, November 9th, 2009

Drake remains steady on the 26.5 N line over the weekend. Depth average current is up to 8 cm/sec.  We continue to find the deep gliders to be easier to fly from point to point.  Currents are smaller over their range of operation.  We are much closer to being a ship than a drifter.  The shallow gliders are more like half ship, half drifter.


The Jet Stream continues to meander across the basin, leaving clear skies over the Middle Atlantic Bight and over Spain, but with Drake in clouds.  Very different from last week.


The Satellite sea surface temperature maps are starting to come in.  There is about a day delay.  The clear areas to our west are showing up now.  Maybe later today or tomorrow we'll have SST back.


Satellite altimetry shows that persistent current running just along 12 W to Lisbon.  That is our escape route if things go bad.  Get into that current, minimize surfacings to avoid ships, and recover from Lisbon if we have to.  The targeted eddy inside the Spanish EEZ shown in green appears to look more like a loop in this jet rather than an eddy.  That will complicate the recovery process.  Still, its good to be thinking about a recovery process rather than the alternative.


The north-south component of the ocean current reported by Scarlet has been fluctuating rapidly, sometimes to the north, sometimes to the south.  It is too rapid for us to follow with an 8 hour update cycle. However, the east-west component of the current is steady to the east.  So we'll take advantage of that and just fly east.  We can let the wobbly north-south component change sign as it decides, while we use Scarlet's velocity to increase the eastward component.  The distance to the Spanish EEZ is down to 98 km.  Distance travelled along the path length from New Jersey is 7120 km.  Distance made good on the last 8 hour segment was just about 7 km.


Today at the 11 am surfacing, we'll check out how Scarlet is flying, and likely make our final pitch adjustment to increase her forward speed.

A steady hand on the rudder

Sunday, November 8th, 2009

Scarlet's task for the rest of the weekend is to maintain a steady  course along an ENE line towards the Spanish EEZ (thin white line).  The currents have been relatively steady to the NE, so Scarlet has kept her heading to the SE.  The target angle separation between the water velocity and Scarlet's glider velocity relative to the water is 60 degrees.  Separation angle on the last segment was 58 degrees - pretty close.  We'll maintain this configuration of crabbing a bit into the wind until the ocean currents change, or we reach the EEZ.  I suspect the currents will change first. We'll have updated altimetery maps for the 11 am surfacing.  Right now, we keep the waypoint the same.  Distance to the Spanish EEZ is 117 km.


Looking ahead, the monday 11 am surfacing turns out to be an important one.  Our distance made good was on the last 8 hour segment was 8 km.  Sometime early monday we will cross the line that is 100 km from the Spanish EEZ.  This is the point we are saving for Scarlet's final pitch adjustment to maintain her speed.  It will be that last 100 km sprint across the EEZ and into the recovery eddy.  Once in the EEZ, the flight path turns to center seeking on the eddy.  We want to get into the eddy and stay there.  The currents just east of 12 W  are strong and will advect us south out of the area.

Winds and Waves on the Eastern North Atlantic

Saturday, November 7th, 2009

Drake is heading into the strongest northward currents along the western side of the clockwise rotating eddy centered near 51 W.  He is having no trouble maintaining the sampling line, running straight along 26.5 N.  In the image below, we have increased the scale of the current vectors by a factor of 3 - instead of the white vectors representing the equivalent drift over 1 day, the green vectors represent the equivalent drift over 3 days.  Even though the currents reported by Drake are the average currents over the upper 1200 m of the ocean, the directions are in excellent agreement with the geostrophic surface currents calculated from the sea surface height measured bythe satellite altimeters as shown on the map.  The current magnitude observed by Drake is a steady 4 cm/sec.


On the other side of the Atlantic, Scarlet  is reporting stronger currents than expected from the sea surface height maps.  Scarlet's currents are averaged over the top 150 m.  Today the peak reached 23 cm/sec.  Here we are showing the white arrows which are equivalent to 1 day of drift. The strong currents to the northeast are moving us along a more northerly path than expected.  To compensate, we'll point Scarlet to the southeast.  The angle between the current vector and Scarlet's own velocity relative to the water is about 60 degrees.  We'll keep that angle about 60 for the night and early morning.  If currents rotate more to the north, we'll increase the angle to around 90.  If they rotate towards the east, we'll decrease it.  We are trying to maintain the track between the thin white path line that spirals into the green circle and the region of high uncertainty indicated by the red circle to our north.  Distance to the Spanish EEZ is down to 127 km.


So why are the surface currents derived from the satellite altimetric measurements of sea surface height in better agreement with the deep currents reported by Drake and the shallow currents reported by Scarlet?  Are the differences just random errors in the altimeter data?  One thing to check is for unresolved eddies in the sea surface height field.  For those we look at satellite sea surface temperature maps.  But when you pop up the SST for Scarlet, you get patchy data.  Overly the clouds and you see why.  That straight band of clouds running east-west across the Atlantic is not a stable configuration for the atmospheric Jet Streams.  Straight jets like to develop waves that grow rapidly in amplitude.


If we check out the Jet Stream forecast, we see the sine wave that now runs across the full Atlantic basin is indeed associated with the Jet Stream. It llooks like those upper level winds are heading right at Spain.  Nice if you are an airplane heading that way.  Not so good if you are a ship.


Jet Stream forecasters also overlay the cloud images on their forecasts for you so you can see the relation directly, saving you the trouble of importing the image into the universal  Google Earth.


How do the lower level winds look in response?  Are these causing the observed differences between Scarlet's depth averaged currents and the satellite altimeter's horizontally averaged surface currents? We can check out the surface winds from ship reports at Oceanweather.  Strong surface winds from the northeast today.  Ekman theory says we should be piling up water between the Azores and Spain right now, so thats not it.


Strong surface winds also mean strong surface waves.  Again heading to Oceanweather, we see forecast waves off the Spanish coast are running over 5 meters (15 feet).


So lets check the wave buoys at Puertos del Estado.

The Cabo Silleiro buoy is closest. Waves heights are approaching 8 m.  Periods are long, as expected with that nice long fetch, but 8 m is still pretty big waves.  As winter approaches, these big waves become more and more common off Spain.  So we race the winter.


7 Gliders get ready for the weekend

Friday, November 6th, 2009

The deployed fleet has grown to 7 gliders.  There are 5 in the Middle Atlantic Bight on a coordinated model-directed coastal mission, plus Drake & Scarlet on Trans-Atlantic missions.  All three regions look relatively cloud free today.


The Mid Atlantic is a glider party, Jersey style.  Somewhere in all that traffic is the new UDel glider, the Blue Hen. Check out the Middle Atlantic Bight blog for an update from Oscar.


Drake is doing fine heading east along the 26.5 N line. I like how it used the eddy between 53W-55W to make the turn into the eastward line.  Its amazing how the surface currents from the altimeter line up with the depth averaged currents from a glider undulating between the surface and 1200 m.  Drake is just now starting to encounter the northward currents from the clockwise eddy centered near 51 W.  Drake has an excellent weekend ahead of him.  Can't wait to see how he does.



It looks like Scarlet has made it past that small current to the NE  that threatened to whip her around in a tight circle back to the west.  Last night shifted the waypoint just a bit to the south to help ensure that this would be the morning outcome.  Today at the 11 am surfacing we'll go back to an easterly course.  Currents where within only a few degrees of Scarlet's course last night, so we got a good read on her speed.  Scarlet's current speed relative to the water is 16 cm/sec, or just under 14 km/day.  Last week's estimates where about 15 km/day.  So she is slowing down.  We have 1 more pitch adjustment left. After that, we start flying too steep for the attitude sensor.  Plan for the weekend is to continue flying east to about 14.5 W.  At that point we start the turn to the northeast towards the green circle of the pick up zone. This morning's distance to the Spanish EEZ is 170 km.  091106_ru27_alt_zoom

Waypoint change to east

Thursday, November 5th, 2009

Scarlet's reported ocean currents are much lower the last three surfacings, down to 5 cm/sec.  If this holds, it means we successfully made it out of the swift currents to the south by flying perpendicular to the current.  It also means we can fly the direction we want.  Following the white pathline into Spanish waters calls for an easterly course at this time.  We'll make the change at the 11 am surfacing.