Water Bodies and Stationary Current Conditions at Boundary Surfaces 457 



According to equation (XIV. 7), stable boundary surfaces on the rotating earth are 

 usually inclined and are horizontal only when the specific momentum pv (velocity 

 impulse) is the same in both water bodies. When/= 0, that is at the equator, discon- 

 tinuity surfaces are of course always horizontal. The following rule can be deduced 

 governing the inclination of the boundary surface and of the physical sea level for 

 steady frictionless currents in the Northern Hemisphere : In every water body there will 

 be a geostrophic current ; looking in the direction of the current (downstream) the 

 isobaric surfaces and the physical sea level will rise from left to right. The lighter water 

 body will be situated on top of the heavier as a very sharp wedge and will move to the 

 right relative to the heavier when looking from the heavier towards the lighter. In 

 the Southern Hemisphere this will, of course, be reversed (it is simply necessary to 

 replace "right" by "left"). 



A good example of steady current conditions in the simplest form is found inside the 

 current system of the East Greenland Current. Here a cold low-saline water mass 

 flows along the coast towards the south; on its left-hand side it borders against the 

 almost stationary Atlantic Water in the middle part of the European North Sea. 

 The main core of the East Greenland Current keeps to the west along the shelf of the 

 east coast of Greenland. Figure 200 shows a density section across the current according 

 to the observations of the "Belgica" expedition (Amundsen). In the vicinity of the 

 current the isopycnals rise with a mean gradient of 1 :300 towards ESE. The water 

 of this cold low-saline current is strongly stratified and especially at the surface there 

 is a strongly heated, very light top layer. The isopycnal, o- = 28-0, indicates the boundary 



Fig. 200. Density cross-section normal to the East Greenland current according to the 



observations of the "Belgica" expedition and the observations of Amundsen. (The small 



map contains the position of the cross-section and the stations used.) 



