Archive for November 21st, 2009

Small Steps Along a Historic Route

Saturday, November 21st, 2009

Tina changed Scarlet's waypoint from Antarctica last night and turned her to the Northeast.   I know, nothing particularly newsworthy about a scientist in Antarctica flying an underwater glider off the coast of Spain, except for yesterday's visitors to the glider lab at Palmer Station. Below is a picture of NASA Astronaut Neil Armstrong and his wife Carol (front row) sitting with RU06 (second row) and Rutgers scientists Brian, Tina and Alex (third row) in the Antarctic snow just outside the Rutgers glider lab.  The gray boxes are the glider shipping containers for the Antarctic fleet.  For the folks at Puertos in Spain, we just sent two of those same crates to Vigo filled with equipment a couple days ago.

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Another remarkable thing about last night's waypoint change was that it was based on ocean forecasts.  Antonio has a new glider pathfinder system he calls Pinzon, in honor of Martin Alonso Pinzon, the Captain of the Pinta.  Antonio noted that Scarlet was in a similar situation as Pinzon and Columbus back in February of 1493. Their story as Antonio told me is that the Nina and the Pinta had just suffered through a great storm where the Pinta was severely damaged, and were left struggling with strong westerly currents. Columbus chose the southern route with the Nina towards Portugal, but Pinzon, in the damaged Pinta, was dragged by the westerly currents, and could not keep up.  Pinzon decided to steer his vessel north rather than head try to fight the currents, and when the wind switched to the Southeast, he turned the Pinta towards Baiona.  

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For the last 4 days, Scarlet has been experiencing stong currents to the west and southwest, greatly slowing our progress.  We have been steering her generally to the north, zig zagging with the currents, fighting for every kilometer in the east direction while trying not to loose ground to the currents pushing us south.  We have only traveled 29 kilometers over the last 4 days fighting these currents.  But yesterday, we have forecasts from both sided of the Atlantic saying the currents would change today.  Antonio's pathfinding program reads the forecast data files and plots a best course, suggesting Scarlet follow Pinzon's route, steering north till the wind shifts and then heading east.  Based on the forecast for today, Tina turned Scarlet last night.  The 3 am surfacing has currents to the southeast, the first easterly currents we have seen in 4 days.  We hope this trend continues.

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 Checking the Navy HYCOM forecast, we see the currents are heading northeast over much of the region.  We turned Scarlet to fly directly downwind with these currents.  Our hope is to move us closer to shore for the pick up in early December.

 

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Comparing the HYCOM currents with the geostrophic currents observered by the altimeter, there is not a lot of agreement.  But there is a reason for this.  The geostrophic currents is the component of the current forced by the highs and lows of sea surface height.  These currents change very slowing.  HYCOM includes all the influences on the currents, including the winds and tides.  There is going to be a lot more variability in the HYCOM model than the geostrophic currents, and as we get closer and closet to shore, that variability will begin to dominate.  Antonio suggests it is time to start reducing the time between surfacings now that we are in the Spanish waters where the variability will increase.  When people are back in the COOLroom on Monday, we'll start the process of reducing the time we spend underwater, first from 8 hours down to 6 hours.  As we get even closer, we'll consider the next step down from 6 hours to 3 hours.  These steps are standard procedures for bringing a glider home.

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One good thing about the recent stormy weather is that the clouds are moving past us.  The clouds are now over the Spanish mainland, with a clear patch opening up over Scarlet.

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Zooming into a SST only image, we see Scarlet in a relatively warm patch if we focus on a west to east transect along 42 N.  Further to our east is a patch of cooler water moving south, and beyond that is a patch of warmer water moving north.  If we follow these currents around the loop, the northward moving leg flows right along 10 W with all the shipping traffic.  This is something we need to avoid, and another reason for choosing the northern route as did Pinzon.

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Looking further up into the atmoshphere, we have the map of the Jet Stream showing the sharp turn to the left it makes as it approaches Spain.

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Overlaying the jet stream map on the satellite images of the clouds, the jet stream is bring clear air from south of Greenland over Scarlet and cloudy air from the tropics over Spain.

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The surface weather chart from Oceanweather has stong winds along this path running across the Atlantic from Canada to Spain.

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The result is big waves.  At least the 30-35 foot (orange-red) waves are north of us.  We are in the green zone, around 20 feet.

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Checking the Puertos wave buoy, they are getting 5 m waves closer to shore.   We'll hope for a window with 2 m waves in early December.

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