Posted by Olaf Boebel on May 15, 2001 at 02:27:24:
In Reply to: drifter eddy measurements posted by Toby Garfield on May 13, 2001 at 21:51:59:
Dear Ron and Ian,
Congratulations to your very nice poster contribution, which I read with great interest. I must agree with Toby Garfield's comment, that there is not a reliable way to determine the eddy diameter from a single trajectory. However, our recent comparison between MODAS SSH and float trajectories (see Boebel et al. poster of this VPS) shows that the floats have a tendency to prefer the 'high velocity' areas, in this case the max speed region of the eddy. This hasn't been quantified yet, and might be just an illusion, because the "tails" of the float images are longer in the high velocity region and hence more 'visible', but that's at least my impression. It might be possible that a convergence is associated with the high velocity/steep gradient regions, which would draw the floats into them, at least for an open ocean current.
A while back we included a similar, though limited, analysis of eddy characteristics in a study of RAFOS floats for the 1994-1996 period. I just plotted the numbers (16 data points) on your figure 4 (Rossby number versus diameter), and they agree nicely with your class 2 eddies. The results for those eddies might also enhance your table 4. For details please refer to:
Boebel, O., C. Schmid, and W. Zenk, Kinematic elements of Antarctic Intermediate Water in the western South Atlantic, Deep-Sea Research II, 46 (1/2), 355-392, 1999.
and
Boebel, O., C. Schmid, G. Podestá, and W. Zenk, Intermediate water at the Brazil-Malvinas Confluence Zone: a Lagrangian view, Journal of Geophysical Research, 104 (C9), 21063-21082, 1999.
At first I was surprised by your result that warm core eddies are smaller than cold core eddies, but your explanation given in the following paragraph of the Results section sounds convincing.
Cheers, Olaf