452 Water Bodies and Stationary Current Conditions at Boundary Surfaces 



field is thus a concentration of the isotherms parallel to the dilatation axis and the 

 horizontal temperature gradient will increase very strongly (according to theory 

 indefinitely). This, therefore, leads to the formation of discontinuity surfaces the inter- 

 sections of which with the sea surface show as discontinuity lines or fronts. 



Fig. 198. Deformation field and the change of a field of a characteristic water property. 

 a — a, shrinking axis; b — b, axis of dilatation; 1 — 2, isolines of the property in the begin- 

 ning; r — 2', isolines of the property at the end of deformation. 



The formation of strong horizontal gradients in the boundary regions of water 

 bodies actually occurs most often in association with stationary oceanic deformation 

 fields. However, other circumstances are involved in their maintenance. These are 

 coupled with the effect of the deformation field and may lead to stationary fronts which 

 are particularly characteristic for the horizontal distribution of the oceanographic 

 factors. For an initially meridional temperature gradient and a steady meridional 

 ocean current v the conditions will develop along the following lines (see Pt. I, p. Ill): 

 the temperature &■ at a fixed point will change according to the relation (positive 

 >-axis directed polewards) 



d^ 1 d^ 



dt 



dv 



If V is directed towards the pole, the temperature at a fixed point will increase since 

 dd'jdy is negative (temperature increase by advection), that is, the isotherms will 

 be displaced towards the pole provided that Q is small. However, due finally to 

 the increase of temperature the first term on the right-hand side will also be increased 

 and as a result all the factors aff'ecting the temperature will maintain an equilibrium 

 state. Although the ocean current is directed towards the pole the temperature 

 distribution will remain stationary. Similar reasoning will also apply to the hori- 

 zontal distribution of other oceanographic factors. Besides stationary fronts of 

 this type there are also frontal formations due to aperiodic occurring processes. 

 However, due to the lack of synoptic observations the course of these usually can- 

 not be traced. An interesting case has been given in Pt. I, p. 182 in the discussion 



