Saturday, March 22, 2008

Time to Exit




Clouds still cover most of the gulf stream we are interested in, Cold air blows over the land from the northwest, heads out to sea over the cold water and stays clear, then hits the warm stream and clouds appear. Typical wintertime scenario. Donglai knows the winds are from this direction, Louis talks of the cloud formation. RU15 is in a strong current to southeast. As it makes this turn, around the bottom of the trough, we want it to start heading to the northeast, then north to get out of the stream. A good way to do this will be to use all the glider velocity to head to the north, and let the Stream do the east component. This means we just head the glider towards the point where we want to pick up the warm ring. That point is number 3 on my waypoint list in the powerpoint I sent last night. The present location, point 2 and point 3 line up almost on a straight line at this time. It flies nearly corner to corner on a 1 degree square. Present location near 38 N, 64W, intended location is 39 N, 63 W. Corner to corner on a 1 degree square should be about 140 km at this latitude. The location of point 3 is 39 00 N, 63 00 W. It will fly us perpendicular to the current. I think the waypoint has to be less than 200 km away for it to be accepted as valid. If it is too far, the second point in my waypoint list still splits the difference. it goes to 38 30 N, 63 30 W. The more distant waypoint (#3) has the advantage of giving us a longer time before we have to change waypoints again. If we need to use the second waypoint, one way to do this is to put the second waypoint in with a big watch circle or about 25 km. As soon as we get close, we go to the third waypoint. If it looks like we are going to miss the second point, then we take over manually and switch to the third. If we miss the waypoint on this surfacing, that is ok. Dave has it going to a point along this same track. RU15 is getting close to the point Dave set early this morning, so we will have to change it soon anyway.






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