deep-water results. The uncertainty of the absolute 

 shape of the Geoid remains, but it enters the problem 

 in a different way. The satellite must reach latitudes 

 as far north as 44° in order to provide useful information 

 on this problem. 



Tracking eddies . The third way in which the satellite 

 program could contribute to our knowledge of ocean circulation 

 is through the tracking of eddies in mid-ocean. Meteorologists 

 know that to understand the dynamics of atmospheric circulation 

 they have to track the numerous high - and low-pressure cells 

 as they move across the continent. Oceanographers, however, 

 at present must rely almost entirely on steady-state models 

 of the circulation, in which the eddy processes are represented 

 in only a parametric way by the so-called Eddy coefficients. 

 Unfortunately we do not really know how important the 

 eddies are, in the dynamics of ocean circulation. We do 

 know that we need to find out; and in fact this is the goal 

 of a large cooperative venture called "MODE", for Mid-Ocean 

 Dynamics Experiment. If the satellite program could find 

 and track a large number of eddies over a period of several 

 years (perhaps indefinitely, if we are to talk about ocean 

 weather) it would provide a very valuable contribution. 



It will probably be only the larger eddies that can 

 be found by the altimeter. Eddies that have been spawned 

 from the Gulf Streain will have a relatively large signal -- 

 initially as large as 1 meter. A typical eddy near the 

 stream may have speeds of 3 knots and be 100 kilometers 

 across, to give a topographic relief of 35 centimeters, at 

 40 degrees latitude. At lower latitudes, the geostrophic 

 balance is achieved with smaller slopes. The more common 

 eddy, far removed from a major boundary current, and produced 

 by a variety of mechanisms, may have speeds closer to 5 cm/sec 

 and a width of 200 km, to produce a topographic relief of 

 only 5 cm. I suspect that this signal will be beyond the 

 reach of the altimetry program.... but we do not know to 

 what extent the topographic signals coincide with temperature 

 signals, or how large the signals really are. At middle 



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