Archive for the ‘Flight to Halifax’ Category

Eastward to the Halifax Line

Tuesday, April 15th, 2008

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.

A Quiet night on the Scotian Shelf

Sunday, April 13th, 2008

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.

Crossing the Shelf Break – A Friday Night Course Change

Saturday, April 12th, 2008

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

Saturday, April 12th, 2008

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.

Halifax Section

Friday, April 11th, 2008

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

What a difference a month makes

Tuesday, April 8th, 2008
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

Tuesday, April 8th, 2008

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.

On to the Next Eddy

Monday, April 7th, 2008

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.

The Route to the Shelf Break

Saturday, April 5th, 2008

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.

Warm Current Loop Right off NJ Shelf

Thursday, April 3rd, 2008

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.