Monday, April 28, 2008

A Weekend Storm

Satellite Sea Surface Temperature (colors) image shows the clouds (white) associated with the weekend storm.

Strong currents to the west blowing us off the Halifax line. New waypoint set for offshore, HL3, perpendicular to the currents and back to the line.

Currents are stronger than we can fly against. Just have to wait them out.

Temperature section shows the surface layer deeping with the storm.

Fresh water at surface looks to be mixed with the water below.

Friday, April 25, 2008

Flight Tests

We just completed a work week's worth of flight tests on RU15 while coming in along the Halifax line. Some watching closely will noticed that we slowed down a bit midweek, even though currents were slow. We were testing the buoyancy pump. Instead of pushing and pulling a full cup of water, we tried smaller changes in buoyancy to see how the energy savings would effect our flight characteristitics. Pulling in less water slows the glider and saves energy on the pump, but then it takes extra time to get somewhere so you burn energy just keeping the lights on. The tests will help us optimize the settings for long duration flight. We are now back up to full speed.

The deep basin off Halifax turned out to be an excellent test bed. Water over 100 m deep that is so close to shore. So we took advantage of the natural topography on the way in.

We are now half way between HL3 and HL2. We moved the HL2 waypoint a bit to the northeast so that it is in between the shipping lanes.
RU15 is now set to just bounce back and forth between the point between the shipping lanes and HL3. We'll keep this pattern going for several days.
We'll keep one eye on the battery and the other on the weather. Scott & Marlon have all the equipment for recovery and a boat ready when its needed.

Currents are small. We need to line up that strong current jet to the northeast with some of the features in the temperature and salinity sections below.

Temperature section inbound on the Halifax line. Three layers. We really like the deepwater test bed we found on the way in.

And Salinity. The surface is freshening.

Monday, April 21, 2008

Progress Along the Halifax Line

RU15 made fine progress along the Halifax Line over the weekend. We are now 95 km from HL2. The SST image again highlights the advantages of an approach from the southeast. We are in the warmer water, that appears to head towards shore along this line and on the upshelf side. On the downshelf side of the Halifax Line, colder water appears to be heading south, against the direction we would want to head.

Currents remain low, 5 to 20 cm/sec.
Following Temperature and Salinity Sections are along the short piece of the transect indicated by the green (start) and red (stop) dots. We are crossing over the bank, and will be crossing back down the shoreward side as the day goes on today.

Above temperature section starts on the offshore side of the Halifax Line near HL4 (green dot above) and heads in towards shore. Nearly 70 km has been sampled. Three clear layers. A warm surface layer (5C), cold middle layer (3C), and warmer bottom layer (6C). As usual, plenty of fine scale structure for the modelers to average out. The location of the bottom showing the bank is indicated by the black color filled area at the bottom of the plots.

Salinty is also three layers, surface (32.2), middle (32.6) and bottom (33.4).

Friday, April 18, 2008

Last Leg

RU15 hit the HL5 waypoint this morning and is now turned and heading towards Halifax inbound on the Halifax line. Currents are low, we are running about 10 cm/sec or less. About 140 km to HL2, so about a week.
Batteries still looking good, as far as you can tell. Time to settle into a scientific sampling section to go with the shipboard data currently being collected.
Here's once example of the 3-D view of the full dataset so far. We'll be presenting this to K-12 teachers at tomorrow at Liberty Science Center. They have an activity to build their own gliders out of legos and stuff. NJNetwork is going to film our undergraduates with the gliders on wednesday next week. They asked for copies of any video or stills taken from the deployment or recovery. Finally our students will be presenting their work on this flight to the public on the Ag School's Field Day next saturday, which is near the time we can start thinking about recovery. NOAA asked for a quick 100 word write up for their newsletter. We have some great I-COOL stories to share. Thanks again to our Canadian partners.

4.74 km to the Halifax Line

RU15 just surfaced 4.74 km away from HL5, the outermost shelf point on the Halifax line. We should be there sometime later this morning. At that point we'll make the turn in. Mostly clouds in the imagery this morning,
so we'll see how that develops. Currents have remained low, so its not as critical as it was in the Gulf Stream region.
Here is the nearly final section that started when we left the Warm Core Ring, crossed the slopewater and shelfbreak, and made our way east to the Halifax line. Almost there.

Temperature along the section. nearly the full water column on the shelf is cold, something our battery guru's will be watching. At the right end of the section, you can see the black shading for the bottom trace, indicating that the altimeter has now been turned back on (thanks Scott M!)

Once we hit HL5 and make the turn, we'll start a new section on the webpage and configure things for a standard cross-shelf line. There is a shipboard cruise going on right now, so we hope to contrinbute some scientific data to that project on the way in. A new area for us, but we benefit from a lot of local knowledge up in Halifax. Thanks again to all up there for sending their help to bring this thing in.

Tuesday, April 15, 2008

Eastward to the Halifax Line

This Satellite Sea Surface Temperature Image pretty much sums it all up. Last week RU15 followed the narrow band of warm water northward up to the deep side of the shelf break. Note that while it was in deep water, the track of RU15 has that serrated knife edge look to it characteristic of the presence of inertial waves. A look back at current vectors from John's time series plots shows the expected rotation of the velocity vector.
RU15 then successfully crossed the shelf break over the weekend, and went far enough onto the shelf to pull out of the currents that were heading southward, back across. Currents remained low Sunday and Monday, as we continued northeast. With good progress being made, we switched our target on the Halifax Line to HFX5, the outermost point that is still on the shelf. From HFX5 we'll turn to the northwest and follow the Halifax line in. Estimated time to Halifax is about 12 days.

Once we reach HFX5, we'll start up a new x-section plot on the webpage. That should happen sometime thursday or friday.

Back home in New Jersey, RU05 left Massachusetts on April 3. RU05 should be hitting the offshore side of the Tuckerton Endurance Line about the same time as Ru15 hits the Halifax line.

We also have two more glider deployments scheduled for Tuckerton. If all goes as planned, by the end of this week, you should be seeing RU15 inbound on Halifax Line, RU05 inbound on the Tuckerton line, and RUo7 & RU20 outbound from Tuckerton. All from the comfort of your web-browser.

Sunday, April 13, 2008

A Quiet night on the Scotian Shelf

RU15 was successfully retasked to fly to the northeast, heading for the relatively warm and clear waters identified yesterday.
Currents are low, and not terribly different from the forecast we found.
A test version put together over the weekend is above.
You need to load it and something like double click on it to get it to zoom in to the "curly" vector forecast currents. Based on where the glider is now, the forecast says currents are to the southeast and low. The glider is reporting low currents more to the south. This could end up being a very useful tool with comparisons in this general agreement. We'll work more on this forecast product visualization on monday. It also sounds like Marlon is finding some relevant Canadian forecasts we can start looking at.

We are back to full water column sampling. The above section starts when we left the Gulf Stream Ring and started crossing the slope water. Most recent data is on the right. Surface temperatures are running about 2C. We want to head northeast into the water with 4C surface temperatures. RU15 has been on quite a journey. In the Gulf Stream we were looking at the differences between 22C in the Stream, 18C in the ring, and now we care about 2C versus 4C.

Saturday, April 12, 2008

Crossing the Shelf Break - A Friday Night Course Change

Here is the track map with the recent current vectors plotted. The new waypoint to the northwest discussed in the previous posting is shown. The issue was the strong currents to the west last night. We wanted to head east towards the Halifax Line, but we had no choice. Dave IM'ed in about 10 pm and said the currents are kicking RU15's butt. The deep ocean was pushing us west. So on friday night we decided to abandon the flight to the east on the deep side of the shelf break, and instead make the jump north onto the shelf, into shallower water, and, hopefully, weaker currents.
Dave changed the waypoint from straight east to straight north, and we switched to a stay deep behavior to avoid the stronger surface currents, flying between a depth of 30 m and 100 m. By morning we had crossed most of the shelf and were getting into slower currents.

Here's the plot of current speed and direction during the crossing. Lots of strong currents to the west on 4/11 that caused the problem. But as soon as we crossed, currents turned to southeast and tried to push us back off the shelf. The good news - at least it had an easterly component.

Here is a zoom in on the track. Our attempt to fly east did nothing but cause the small loop in the track just offshore the shelf break. We gave up on that and jumped across. Now that we are on the shallow side of the shelfbreak, we are heading northeast, towards the Halifax line and the favorable currents identifed by Scott & Marlon in the previous post. We are back to full water column sampling.
We have a much more restful night ahead of us.

The Approach to Halifax

Scott McLean sent this image last night. Average currents on the Scotian Shelf for spring based on models and moorings. There is a nearshore jet that turns offshore at Halifax and heads straight south. Based on the mean currents, we don't want to approach from the south. An approach from the southeast would be better.
Marlon Lewis sent the Chlorophyll images above (April 7) and below (April 8). Both show high Chlorophyll (red) east of Halifax. The high Chlorophyll water turns offshore at Halifax, heading south, then southwest. Images look similar to the mean flow currents above. These images also say don't approach Halifax from the south. Try to stay in the water with low Chorlophyll (blue) that extends far north along longiotude 62 W.

Last image in the story is the SST from April 11. Only clear image of the area in the last few days. The warmer water on the shelf (blue, 4C) extends
to the north along latitude 62W. South or Halifax, the very cold water (pink, 2C) is extending far offshore.
All this indicates that an approach to Halifax from the south would run into a steady headwind for nearly the entire crossing. It is better to work our way eastward into the relatively warmer (4C), and Chlorophyll free water, and approach Halifax from the southeast. We just changed the waypoint of RU15 to fly to the northeast into the favorable currents so nicely identified by our friends in Canada. Thanks Marlon & Scott.

Friday, April 11, 2008

Halifax Section

From Loder, Shore, Hannag & Perie, 2000. Deep Sea Research.

Tuesday, April 8, 2008

What a difference a month makes

If we left April 8 we would have to travel 230 km further south to get to the Gulf Stream

Gulf Stream March 7, 2008

Gulf Stream April 7, 2008

Favorable currents & a lucky break

RU15 made good progress during the night.
Temperatures are staying low.

A lucky break in the clouds. The only clear area offshore is right over RU15.
A new Zoom region as we approach the shelf break. We are heading east towards the X and the southern end of that eddy.

Currents have increased and are towards the east.

As we approach the shelf break this week, we'll be changing the scales on several of our plots to make them easier to read. Temperature and current scales will be adjusted for the smaller range. The SST Zoom has been zoomed even more. We'll restart the temperature sections so we can see the smaller scale fronts of the shelf.

Monday, April 7, 2008

On to the Next Eddy

RU15 had a weekend of favorable currents that swept it clockwise around the western and northern side of the southern eddy. We exited on the northeast side. After leaving the southern eddy, we retasked RU15 to head to 42N, 63 W based on the last good satellite image. We were hoping to hit the bottom of the northern eddy. Within a few hours we had a clear spot in the clouds. The northern eddy was still there, and we where headed in the right direction.
Heading up to the northern eddy we are starting to encounter a bit of a headwind. The last two vectors are opposing us. Still under 20 cm/sec, so we'll make progress against it. We'll let it run overnight to see if this persists.

Saturday, April 5, 2008

The Route to the Shelf Break

RU15 has looped around the western side of that eddy, and is now heading to the east along its northern side. Satellite imagery from today and yesterday is cloudy, so we can fly based on the image from April 3.
Here is a zoom in on the April 3 Gulf Stream image. The centers of the southern eddy and the northern eddy are labeled. The proposed route is to continue westward along the top of the southern eddy, jumping out on the northeast corner. We then follow the cold water up to the northeast towards the northern eddy. We use the western side of the northern eddy for the boost up to the shelf break.

Thursday, April 3, 2008

Warm Current Loop Right off NJ Shelf

Having the knowledge of the past few days under our belt would we jump into the warm curent ring to get to the gulf stream or avoid it and fly the glider north of the ring.

A close call with a Gulf Stream meander

This picture pretty much tells the story from the last few days. RU15 was near the southern end of the warm core ring centered near 40 N, 64 W. We were spinning around the eddy just outside of the radius to maximum swirl velocity. As we were flying up the western side, the Gulf Stream meander creast that was too our west started coming our way. It seemed like the clouds opened up and there it was. The very next surfacing we turned RU15 more into the ring, and started flying towards the high swirl velocity. We needed to use it to shoot to the north out of the meanders way. We got in and we shot north, at speeds over a meter per second. Its a good thing we did, that meander crest has now propogated downstream to the east, right through the area we were flying in. Notice how the warm core ring that was elliptical is now being stretched out to the south as it is being absorbed into the Gulf Stream. That would have been us with RU15. A fast ticket south when we need to go north.

But then as soon as we were north of the meander crest, we had to apply the brakes. If we stayed in the fast swirl velocity, we would have been swept by the small eddy near 41 N, 64 W. If we missed the free ride from the small eddy, we'd have to fight against a cold headwind to get to the north. So we turned the glider perpendicular to the swirl velocity and started flying back out. We kept changing the waypoint to stay perpendicular to the swirl velocity, just as if you were swiming perpendicular to the rip current. This time around we were close enough to the edge to get out of the warm ring just in time to end up on the south side of that small eddy centered near 41 N, 64 W. We found the cold water that is being swirled around, and turned to the west to start following it around the new eddy. We'll conitune to swirl around this eddy till we get around to the northeast side, probably sometime saturday. Then we'll exit this eddy, jump back into the cold water and follow it to the northeast up to the next eddy up we saw up around 42N, 63W. We'll keep flying eddy to eddy till we make the shelf break. We can worry about most of that over the weekend. Cause tonight, we rest. RU15 is in the small eddy, riding some slow but favorable currents. We'll all get some sleep and check it out in the morning. Our robot is fine - for now.

RU15 enters the small eddy

RU15 is in the cold water looping around the western side of this clockwise circulating eddy centered near 41 N, 64 W. SSTs are about 5-7 C
Currents in the eddy have inceased to about 25 cm/sec. The direction is to the northwest. The glider flies at about 25 cm/sec, so we are doubling our speed over the ground.

New temperatures near the surface on the right a blue, so 6 to 8 C range.

Today's objective is to loop around the west and north of this ring, and shoot out on the northeast side, continuing northeast in the cold water to the next eddy assist.

Wednesday, April 2, 2008

Student Links

Marlon, Scott McL., John C., and other friends in Halifax ------

We have a class of undergrads here at Rutgers that is just having a great time with this. They are scouring the web for datasets, satellite images, model forecasts, altimeter maps, ice maps, wave forecasts, etc, etc. Some are working on the path planning. Others on the conditions in the landing zone. Just like the Stommel race, but this time the race is against the clock. Dave Aragon, our glider electronics tech, has given us 35 more days of flight time (starting today) before we have to hang it up. We think he's built in a safety factor, but he's certainly too smart to tell us what it is.

So RU15 has to stop surfing the Gulf Stream and looping around in the warm core rings and head for a home port. Do you have a similar group of students that we could set up a skype or other video conference with?
Our students would like to talk to yours about the sea conditions, ice conditions, currents, weather, and everything else that comes up when you are searching for a home port. I-COOL edu at its best.

We keep seeing the wave forecasts calling for 7 to 13 foot seas offshore of Halifax. You know from the HyCODE days that waves like that are not something we are used to. Maybe with your help we can bring this glider home and snag a Dalhousie sticker for the hull in the process.

Hope to see you all in a few weeks!

Path Home

Here is the satellite image from today. The red dots are where we are going to send the glider.
This is the path on google earth