Ride the Wave into a 100km Day?
Wednesday, July 2nd, 2008RU17 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).