Archive for July 2nd, 2008

Ride the Wave into a 100km Day?

Wednesday, July 2nd, 2008

RU17 has reached the east side of a large cold core eddy. At long last, we should regain northern velocities during the next segment before they swirl towards the center of the eddy (turning counter clockwise). Since we really don't want the glider to fly into a trap that it has a difficult time getting out of, I will choose way points that send the glider towards the outside edge of the eddy. The glider should not get to the edge for several days, but we've got to start heading for there now. It's all about time, distance, energy and pushing east. The glider's speed through the water is fixed (+/- the weight of remora remora).

Right now, I am choosing the next WP for RU17. Checking the water velocities over the past few surfacings, we can see that the water has begin moving more EAST than SOUTH. By tomorrow morning (between 11:30PM and 5:30AM surfacings), water velocities will be to the NORTH. Since we don't know that RU17 is currently in water moving NORTH, the WP that I choose needs to fly RU17 towards the center of the circulation (NORTH) in case velocities to the SOUTH have become stronger, but should help RU17 fly perpendicular to the current, towards the outside of the circulation (EAST). So, RU17 must cross the line connecting the new waypoint with the center of the circulation. Since velocities should increase to the north, and we want to go EAST, our new WP will be just N of the glider, more importantly, further EAST. When the currents turn towards the NE, as they should over night, we will swim perpendicular to them. Since we would likely begin to drift ENE, our WP will become increasingly SE. We don't know how strongly those velocities are going to be, so it is important to choose a point with the intended heading, but a good ways off. Between the last two phone calls 6hr, we traveled 30km (not too shabby). I hope we do that again, and I'll chose a point ~80km off just in case. In either event, a new WP will be needed for the 11:30 surfacing.

Below, the background colors (orange/red) show the water temperature near RU17. Notice how this reveals the circulation of the water. The blue line segment shows where RU17 should surface, the green line shows RU17's bearing when it surfaces, and the red line shows its new heading. The yellow pin is where the new waypoint is located, and the yellow glider tail shows RU17s last know position (just before its last phone call).


This pattern favors that life is the problem, Remora remora

Wednesday, July 2nd, 2008

We've had several missed climbs for a while now. Yesterday, we found out that these missed climbs happen only between 23:00 and 07:30 GMT. This night time only glider behavior gives stronger indication that the problem is biological, not mechanical (though nothing can be said to be definite). Yesterday before the work day ended, I told myself that I wouldn't be surprised if later that night we saw the same behavior start exactly at 23:00 and end at 07:30 GMT; and I wasn't disapointed (well, it's not like it's a GOOD thing, you know?). Here's a plot below of two segments that span the night. It's the remora again.

As I hear it, remora are visual predators, and thus cannot see well at night. To help them move through the blind night, they attach themselves to other fish and get a free ride that they might not be able to easily make on their own. Our glider probably looks as good as any shark to these guys. At night at 23:00 (or 20:00 in the glider's time zone), the sun goes down and the remora attach themselves to our glider, adding weight that makes the glider struggle to climb with. When the sun comes up at 7:30 (4:30 glider time), the remora can see again so they let go of our glider and thank it for the ride.

I also just found out that in the mid-Atlantic, the Remora spawning usually takes place between June and July. Nice.  We've got to find some way to avoid these guys.

The biggest eddy East of the Grand Banks

Wednesday, July 2nd, 2008

Currents continue to increase in a surprisingly strong eddy. We are starting to loop around the southern side. In this location the models have a lot of southward velocity slinging water off the eddy to the south. We don't want to be thrown into that.

So we are making our way east, trying to stay towards the core.

Somewhere between 47 W and 48 W, the strong southward velocities end.

We should see a turning to the east of the velocity vector.

At that point we need to do the opposite and work on getting out of the eddy.

You'll see a switch in our flight planning from flying towards the center to flying towards the out edge.

Center seeking to center fleeing behavior.

The biggest eddy east of the Grand Banks

Wednesday, July 2nd, 2008

Posting for Scott, he is somewhere on the interstate cruising towards Ohio. Scott says

"The biggest eddy east of the Grand Banks
Currents continue to increase in a surprisingly strong eddy. We are starting to loop around the southern side. In this location the models have a lot of southward velocity slinging water off the eddy to the south. We don't want to be thrown into that.

So we are making our way east, trying to stay towards the core.

Somewhere between 47 W and 48 W, the strong southward velocities end.

We should see a turning to the east of the velocity vector.

At that point we need to do the opposite and work on getting out of the eddy.

You'll see a switch in our flight planning from flying towards the center to flying towards the out edge.

Center seeking to center fleeing behavior."