Numerical Prediction of Geostrophic Flow Derived 

 from Sea-Surface Temperature 



James G. Welsh 



The Travelers Research Center, Inc. 



Hartford, Connecticut 



INTRODUCTION 



The author has previously described the application of the 

 equivalent barotropic model to an ocean of variable depth. This 

 paper extends the model to allow sea-surface temperature prediction 

 and to incorporate the irrotational flow associated with horizontal 

 divergence. A simple approach to deriving a geostrophic flow field 

 from sea-surface temperature fields is described; the inclusion of 

 irrotational flow into the model and the nature of the derived 

 velocity potential for the Gulf Stream are discussed, and experi- 

 mental forecasts of sea-surface temperature for the western North 

 Atlantic Ocean are shown. 



GEOSTROPHIC FLOW EXPRESSED IN TERMS OF SEA-SURFACE TEMPERATURE 



Geostrophic flow in the ocean can be computed when both the 

 vertical distribution of horizontal density gradient and the actual 

 flow at some reference level are known. For numerical prediction, 

 these must be known for the area in which prediction is carried out. 

 Unfortunately, it is only for sea-surface temperature that there may 

 be adequate observations to permit a meaningful depiction of the 

 horizontal distribution. This leaves salinity, the flow at a refer- 

 ence level, and the vertical variation of temperature gradient to be 

 described. It will be assumed that salinity is constant, and the 

 flow vanishes at the bottom. 



The vertical variation of the horizontal temperature gradient 

 VT will be prescribed by 



VT(z) = VT 

 s 



i-f 



n 



(1) 



184 



