(5) A Gulf-wide quasi-geostrophic tilt mode of about 6.5 day 

 period is found in the model superimposed on the volume 

 mode, but verification of this from observations is lacking. 

 The above conclusions are based on a quasi-linear, two-layer 

 model of the Gulf of Mexico and a portion of the Cayman Sea. The 

 model used a grid size of 15' in latitude and longitude and allowed 

 for a varicQDle Coriolis parameter. The lack of non-linear advection 

 and the ad hoc conditions at the open boundaries of the Cayman Sea 

 and Florida Strait should be borne in mind, particularly with regard 

 to conclusion (5). Long period, quasi-geostrophic (planetary) modes 

 are known to exist in the ocean; however, their spatial structure 

 amd behavior is known to be sensitive to open boundary conditions and 

 to non-linear phenomena such as advection of vorticity (which is not 

 admitted in the present model). Indeed, the effect of the strong 

 quasi-steady Loop Current within the eastern Gulf is missing in the 

 present linear model. Regardless of these limitations, it is felt 

 that conclusions (1) through (4) remain valid. 



198 



