158 PETTERSSON OCH EKMAN, SKAGERACKS OCH KATTEGATS HYDROGEAFI. 



The following observations will serve to indicate the principal differences between 

 winter and summer. 



Ä. The uppermost layer of inflowing Avater which has from 32 to 34 °/o„ salt 

 covers the surface of the central part of the Skagerack in wintertinie. In plate II this 

 kind of water is marked green (32 °/oo and 33 7oo water) and extends like a broad band 

 from the west coast of Norway into the large central part of the Skagerack. Its thickness 

 can be judged from section 1, plate III; section 5, plate IV; section 9, plate V, and tig. 

 5, plate IX. 



In July, as will be seen from Ekman's section in plate V, and fig. 6 plate IX, this 

 layer of 32 & 33 water is largely replaced by fresher water from the Baltic stream. The 

 remainder is reduced to so thin a layer that it does not measure more than 2 or 3 métres 

 in the middle of the Skagerack (see Syn and Fm, section 9, plate V). In the vicinity of 

 the coasts it increases considerably in thickness but will still be found very thin com- 

 pared to its volume in the winter. Thus water of 32 & 33 "/„(, saltness enters into the 

 Skagerack at some time in the course of the autumn or at the close of the year and is 

 expelled again, at least to a great part, in the spring by the increasing outflow fi'om the 

 Baltic. This kind of water, containing from about 32 to 34 "/do of salt, we have de- 

 nominated 'bank-water because it is found outside the Skagerack on the Danish and Nor- 

 wegian submarine banks (see plate IX). It has a temperature in February of from 3° to 

 5° C, that of the 32 water being somewhat above 3° and that of the 33 water above 4°. 

 Thus in the midst of the winter the broad central part of the Skagerack has a surface 

 temperature of more than 3° or 4° C. while the temperature of the Baltic stream along 

 the coast is not more than 1° or 2° C. and that of the coast is under zero. This has 

 important meteorological consequences to the climate of the Scandinavian peninsula, as 

 may be seen from the lines of equal temperature on meteorological charts. Another effect 

 of this singular distribution of temperature in the Skagerack is to promote cyclonic distur- 

 bances of the atmosphere. 



This source of heat disappears as a rule at the close of February or in March, but 

 sometimes even in January, because the increasing Baltic stream then covers the heavier 

 and warmer bank-water with fresher and colder water. Therefore the coldest season of 

 the year in Bohuslän ordinarily falls in the last weeks of February or in March. The 

 hitherto unsettled weather then gives place to a period of cold with calras or gentle winds 

 from the E., SE. or NE., as a barometric maximum sets in över Scandinavia. Under the 

 influence of the atmospheric cold the surface temperature of the Baltic stream then sinks 

 below zero until it reaches the freezing point of the water. Chapter VI contains a descrip- 

 tion of the hydrographic conditions of the Skagerack during the winter of 1879. In plate 

 X, fig. 1 represents a section along the coast of Bohuslän in December 1878 and figs. 2, 

 and 3, the same section in January 1879. After a stormy period in December and the 

 beginning of January cold weather with SE. winds set in from the 13th of January- 

 The Baltic stream began to gain in strength, sending wedge-shaped tongues of fresh and 

 cold Avater northwards along the Swedish coast with a velocity of about 13 miles in 24 

 hours. The temperature of every water-stratum sunk rapidly under the influence of the 

 atmospheric cold and when it happened that such a layer of water, which has been cooled 



