662 The Stratospheric Circulation 



2. Polar Currents of the Northern Hemisphere 



Phenomena similar to those found in the subtropical convergence region can be 

 expected also to occur at the polar convergences. These will be even more intensive 

 there, since a much sharper density difference exists between the adjacent water 

 masses. External factors will, at many places, cause the formation of vortices between 

 the warmer highly saline waters of subtropical origin and the cold weakly saline polar 

 waters. These travel along the boundary zone, continually forming and disappearing 

 and thus giving rise to a continuous mixing of the two water bodies. For these reasons, 

 in the Northern Hemisphere, the left-hand border of the polar currents is not sharply 

 developed and here polar waters and water masses of subtropical origin work into 

 each other. This is shown to be true for all currents, especially for the East Greenland 

 Current along its boundary region against the Irminger Current to the south of Iceland 

 and for the Labrador Current where it encounters the Gulf Stream. 



Some insight into the processes involved in the vortex formation in the region of 

 interaction between two adjacent water masses, especially as found in this part of the 

 ocean, has been obtained from the almost synoptic surveys made by U.S. Coast Guard 

 vessels (see the bulletins of the U.S. Coast Guard, International Ice Patrol, 

 Washington). 



The sea around Greenland (Greenland Sea, Labrador Sea, Davis Strait and Baffin 



Bay) has been well surveyed oceanographically by numerous expeditions, and from 



the entire data available it is possible to obtain an idea about extent and course of all 



the currents. This is especially true of the East Greenland Current which can be follov/ed 



along its entire course from the Denmark Strait to Cape Farewell and from thereon as 



the West Greenland Current until it finally disappears (see Defant, 1936^ for 



references). Little information is available on the East Greenland Current from its 



origin near the Spitzbergen Rise to the Denmark Strait but there are appreciably more 



data to the south of this strait. All cross-sections show a similar structure. The polar 



water layer always has a cold core in which the temperature is almost at freezing point. 



Figures 3 10 and 3 1 1 show two cross-sections through the East Greenland Current in the 



Denmark Strait and off Cape Farewell, The analysis of 37 sections of this type through 



the East and West Greenland Currents has enabled the course of the polar water 



flowing around Greenland to be followed in detail. In Fig. 312 an attempt has been 



made to show the boundary separating polar water from Atlantic water; in addition, 



the average minimum temperature in the core layer of the polar water is indicated in 



this figure which is usually at a depth of 80 m. The minimum temperature in the core 



layer gradually rises from — 1-7°C in the Denmark Strait to about — 1-0°C at Cape 



Farewell. Past the southern tip of Greenland, where the current turns sharply around, 



the core layer rises towards the surface; its temperature increases rapidly and from 



about 61° N. on is usually no longer negative. The East Greenland Current from the 



Denmark Strait southwards where the width of it is more than two-thirds of the width of 



the strait remains entirely over the shelf; where the shelf is broad the current is also 



wide and where the shelf is narrow (for instance between 62° to 63° N.) its width is 



very small and does not exceed 25 to 30 nautical miles. The lens of cold water forming 



the current core at first extends well to the east, but becomes smaller towards south and 



shrinks from the Denmark Strait to Cape Farewell under the impact of the warm 



water of the Irminger Current. It is, however, still present and shows that the polar 



