Posted by Toby Garfield on May 13, 2001 at 21:51:59:
It is good to see an analysis of the range of eddies in the "Eddy Zoo" found off the South Brazilian coast. The authors have done a good job of extracting information out of two potentially frustrating data sets.
While the authors make mention that buoys do not measure the true size of an eddy, they make no effort to explore this problem, one that plagues anyone using drifters. If the buoys are located in the outer perimeter of an eddy, then the computed velocity could easily be lower than the main body of the eddy. However, the truth is that there is no accurate way to estimate the eddy diameter from float trajectories. If the eddy is in solid body rotation, the Rossby radius may be correct, but there is no way to determine the ratio of D/Rd.
I am surprised there is no dicussion of other mechanisms for the high frequency small eddies found on the shelf. Surely the tidal and inertial effects can not be dismissed. I did not find any suggestion of editing the data to remove these effects.
I suggest that the authors examine Sanderson 1995 (JGR 100, 6761-6776) for a nice numerical technique for determining the rotational and translational components of drifter tracks.
One final comment, it would have been nice if the trajectory "tails" remained on the animation until the completion of the mission for the float being animated. I found the animation a bit hard to keep together.