Archive for October 17th, 2009

Fleet Update on a Stormy Saturday

Saturday, October 17th, 2009

Art Allen and I have been travelling around the U.S. and Europe talking about mapping surface currents with HF Radar  and how it is being used to improve the Coast Guard's Search And Rescue planning.  At dinner, the conversation inevitably turns to hiking up mountains. Art is expert at this - he's even an instructor at what they call winter school. My younger daughter and I have become fans of the Appalachian Trail as a result, and Art keeps urging us higher and into more adverse weather.  My weekend blogging has suffered as a result, but this weekend is just too stormy.  The weather reports are talking of twin northeasters.  So lets go to sea instead.

The deployed glider fleet is currently concentrated in the North Atlantic.  RU15, RU22 and RU23 are just visible through a break in the storm clouds off the U.S. east coast. Drake is heading away from the Virgin Islands and RU27 is heading towards Spain. Gliders are being prepped in Antarctica by Tina and Alex.  Back at Rutgers in the glider lab, vehicles are being readied for California in November, and are being lined up for the big NSF Ocean Observing Initiative Experiment in the Middle Atlantic Bight starting at the end of October. 

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The weather on the U.S. east coast is bad.  Northeast winds and large waves.  Its not great offshore Spain either.  Again, northeast winds.  This could help explain some of the currents we are seeing with RU27 later in the blog.

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Starting with the Middle Atlantic Bight, we have three gliders deployed on the continental shelf.  RU22 is the Integrated Ocean Observing System (IOOS) glider which is on a water mass mapping mission that fisheries scientists will use to relate to their fish distribution data.  it will be picked up by the IOOS regional glider port at UMaryland after the storm. RU23 is on a mission for the Navy.  It is the first Slocum glider equipped with the rechargeable lihium batteries and it carries the new Seabird pumped CTD.  The results of this mission will be presented at the European Glider Organization meeting in Cypress next month.  Too the north, our IOOS partners at University Massachusetts just deployed RU15 for an Office of Naval Research mission.  It has a full up optics package - they most advanced I've ever had a chance to see.  It has 2 Eco-pucks and the Navy's new Beam Attenuation Meter, or BAM sensor as we like to call it.  All are providing temperature and salinity data for assimilation by the IOOS ocean modelers at UMass, Stevens and Rutgers.  All three IOOS modelers are getting spun up with this dataset in preparation for the NSF experiment beginning at the end of this month.  Its going to be quite a party.

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But our most immediate objective was to get RU15 with its hot optics payload into the water before the twin northeasters hit.  Hugh, Ethan and Erick from Rutgers worked their partners at UMass, Old Dominion and U. North Carolina to make sure they had the full Mid Atlantic HF Radar network up and running for this storm.  Thats good, because last thursday we just submitted an abstract to the February Ocean Sciences meeting in Portland, Oregon to describe this storm.  We often submit abstracts based on the results we think we are going to get, but I guess that's the first time I've submitted an abstract based on a forecast. As you can see from the regional plot below, the currents are so strong, they swampped our standard plotting algorithm.  Anyone that wants to contribute a good matlab routine for plotting "curly vectors" is encouraged to send us an email.  We put it in place and start generating regular plots with it if you are willing to share code.

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So instead of looking at the full region, we zoom into the areas covered by our three operational centers.  Here is the northern region anchored by UMass and UConn.  Strong currents near 50 cm/sec or greater heading alongshore to the east.

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Here is the central region anchored by Stevens, Rutgers and UDelaware.  Currents over the entire shelf turning southeast.  It looks like the Hudson and Delaware plumes are having some impact during these rains.

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Lastly we to our southern operations center led by Old Dominion and U. North Carolina.  Flow remains alongshore, turning south till it hits the Gulf Stream.  The strong Gulf Stream currents in the image below can be compared to the high Gulf Stream temperatures in the satellite sea surface temperature image above.

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Now lets check in on RU15, where it just left Buzzards Bay on the blue track below.  We have this glider on our standard storm sampling plan that switches it to 1 hour surfacings so we can resolve the tidal currents.

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 Here are the temperature profiles.  The glider is traveling from left to right. The thermocline is deep and just above the bottom as indicated by the warm (red) temperatures above the cold (blue) temperatures.  As the storm hits, the water column gets well mixed to in intermediate yellow color.

 

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Below is the same section in Chlorophyll. Lots of phytoplankton above the thermocline, nothing beow.

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Now, on to my favorite Eco-puck sensor, backscatter at 440 nanometers. Just before the mixing we see the sediment is suspended and mixed below the thermocline. This is what we have seen before.  Then after the water column is mixed, we expected the sediment to also mix throughout the water column.  But where is it?  What is different about this storm than the ones we have been studying from the Office of Naval Research Martha's Vineyard experiment?  The abstract keeps getting better and better as the storm progresses.  And we continue building the array of test cases for the Community Sediment Transport Model.

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Heading south towards the Caribbean, Drake is making excellent progress through the gap between two clockwise rotating eddies.  There are no good routes to the northeast with favorable currents, so we are taking the route with currents perpendicular to our path.  Once we get up to about 26.5 N, we'll turn east and head zig-zag along this line downstream with the meandering currents. 

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Lastly, we head east to the west coasts of Spain and Portugal, and RU27, also known as The Scarlet Knight.  Scarlet was encountering some strong currents to the west that had halted our progress until we turned north to get out of them.  We were not sure of the cause, until we just got a gap in the cloud cover and some new satellite Sea surface temperature data.  John just readjusted to temperature range to cover 16C (blue) to 22C (red) because of the fall cooling, and out popped the answer.  We have a pair of counter-rotating eddies lined up along Scarlets path.  We are in the warm water filament being entrained along the western side of the eastern eddy.  As soon as we hit the wall of this filament, we were stopped cold.  We now know our route around is to stay with this water as we head northeast.  We'll continue on this northeast path up to about 42 N, and then turn east. Reading the distance along the dogleg from our present position to the outer edge of the European Exclusive Economic Zone, I get a distance of 490 km.  Our most recent estimates of Scarlet's speed where 19 km/day and 18 km/day.  

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Zooming into the pair of counter-rotating eddies, we see the warn filament being drawn to the north and then spliting off, with one branch heading west and the other east. We are exactly where we want to be, on the eastern side of the northward flowing filament so when we split, we follow the split to the east.

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Fading out the Sea surface temperature so we can see the surface currents from the altimeter, we get see that the altimeter is getting much of the structure associated with the warm filaments.  But we are also seeing strong currents to the west.  Could we also be seeing the effect of the strong winds that are blowing from the northeast?

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