8 



BJ0RN HELLANDHANSEN 



[REP. OF THE "MICHAEL SARS" NORTH 



a long time taken from a ship drifting with the current. 

 Only when the saHnity is almost constant will the daily 

 variation of temperature exhibit itself clearly, as may be 

 seen from some parts of our curves. But even then some 

 unexpected variations of temperature may be found (cf. July 

 23rd to 26th). When we compare the surface temperature 

 (the B-curves) with cloudiness (A-curves and B-curves) we 

 find — as might be expected — that the daily temperature 

 variations were much more prominent with slight than 

 with extensive cloudiness (cf. June 7th— 9th, 11th, 19th— 

 22nd with slight cloudiness and a distinct daily period 

 of the surface temperature, while the observations from 

 August demonstrate great cloudiness and scarcely any 

 trace of the daily period). 



By means of very extensive material in the form of 

 temperature observations from the sea surface and the 

 air, Professor Nansen and I have studied the annual and 

 monthly temperature variations in the North Atlantic 

 [Helland-Hansen and Nansen, 1917, 1920, 1921]. We have 

 found that temperature-variations of this kind in a definite 

 place (relatively to the sea-bottom) appeared at first in 

 the air and afterwards in the sea surface, both of them 

 being due to general alterations in the distribution of 

 air pressure and consequently in the winds. We came 

 to the conclusion that the variations in surface temperature 

 were chiefly the result of a displacement of the surface- 

 layers. The direct warming or cooling effect of the air 

 upon the sea seemed to be of secondary importance. 

 These results agree with the results we have come to above. 

 The temperature of the water without regard to the geogra- 

 phically fixed place is in close correlation with the salinity. 

 The wind only produces a slight thermal effect directly, but 

 it may displace the surface water, with the result that the 

 variations observed from a fixed point take place in salinity 

 and temperature simultaneously. This effect is gradual, 

 and may be detected by continuous observations at fixed 

 stations or in the average for small areas, but not by 

 means of observations made along a route which is 

 traversed rather quickly. If temperature variations of this 

 kind were not closely connected with the movements of 

 the water, we might expect to record temperature variations 

 which were quite independent of salinity variations. 



It must be borne in mind that the heat capacity per 

 volume is about 3300 times as large for water as for air. 

 An average heating of the air from the sea surface upwards 

 to 300 metres by 1° C will correspond to an average 

 cooling of the uppermost 10 metres of the sea-water by 

 less than 0-01° C. A heating or cooling of the atmo- 

 sphere from the sea will therefore have only a slight 

 influence upon the latter when it is not continued for a 

 long time. 



The wind will, of course, effect a mixing of the upper 



water-layers owing to the waves. When there is a marked 

 vertical temperature gradient in the upper few metres of 

 water quite appreciable temperature-variations may be 

 observed at the very surface. A maximum of temperature 

 as well as of salinity will mostly be found at the surface 

 or in the surface layer in the North Atlantic in summer. 

 It will, however, be seen from the Tables that the tempe- 

 rature gradient for the upper 10 or even 25 metres was 

 very small, so that a stirring by waves would as a rule 

 have only an insignificant effect on the surface tempera- 

 ture. Generally no long time elapses between the occur- 

 rences of fresh winds in the North Atlantic so that no 

 appreciable cumulative effect will be established as far as 

 the vertical differences of temperature are concerned. But 

 some variations of this kind may be expected, and it will 

 also be seen from the A-curves that a high wind velocity 

 corresponded to a general, though small, fall in tempera- 

 ture, irrespective of the direction from which the wind 

 was blowing. A small effect may also be traced in the 

 salinity. 



8. The Air Temperature. 



The A-curves for the air temperature //^ 1 are drawn 



on identically the same scales as the curves for the surface 

 temperature /> 1. The two curves accompany each other 



remarkably closely in all series, and the rapid and great 

 variations in both elements coincide much better than 

 might be expected (cf. June 26th to July 2nd, and July 

 8th to 12th). The curves very clearly reveal the important 

 fact that the mean air temperature had a strong tendency 

 to follow the mean surface temperature. The difference 

 between the two was, on the average, only very rarely 

 as much as T C, even if the air had come directly from 

 Arctic regions with much lower, or from Tropic regions 

 with much higher temperatures. Our curves, in combination 

 with the synoptic charts, prove that the air about 5 metres' 

 height above sea level very quickly adopts a temperature 

 approximating to that of the sea surface. 



The greatest differences fr — r\ of the averages were 



found in the second series of observations between June 27th 

 and July 1st, in a region with rather abrupt hydrographic 

 variations where there is only a short distance between 

 warm and cold water. But even there the two curves 

 exhibit the same great changes. On June 26th the air was 

 relatively cold in spite of a wind, at limes strong, blowing 

 from S, SW, or W. It will be seen from the charts that 

 the air just N of our position on the 27th of June in the 

 morning came from NW with temperatures between 12° 

 and 17° C. On the 28th of June (morning) the wind in 

 places W of our position came from N, while we observed 



