NO. 4 TEMPERATURE VARIATIONS IN THE NORTH ATLANTIC II3 



to 52 show that this on the whole is the case to a high degree, and 

 furthermore they show, what was also to be expected, that for the 

 variations in the air temperature in February the variations of the 

 air pressure gradients in February are of greater importance than 

 those in January. For it is obvious that variations in the wind act 

 more directly upon the temperature of the air than upon that of 

 the water, whose mass is more slowly affected. 



Although our observational material for the air temperature is 

 so imperfect, yet the curves for the air temperatures in February 

 and for the pressure gradients particularly in February show an 

 unexpected agreement for the most of the ocean regions. It is 

 clear that the variations of the air temperature are much greater 

 than those of the surface temperature. It is also to be expected, 

 as already said,- that the action of the wind would not only make 

 itself first felt on the air temperature, but also would produce in it 

 greater variations than in the surface temperature of the water. 

 The investigation of the anomalies of the surface temperature 

 minus the air temperature, as in tables 9 to ii, W-L, must therefore 

 be of interest. These anomalies are given by the curves W-L of 

 the surface temperature minus the air temperature in plates 16 



to45- 



In many fields there is a good correspondence between the varia- 

 tions of these anomalies and the variations of the surface tem- 

 peratures and the pressure gradients. This is particularly notice- 

 able in the average curves for the greater southerly region in 

 figures 50 to 52. It appears, for example, that throughout the 

 years with particularly low surface temperature the air is generally 

 much colder than the water, and therefore the difference between 

 the surface temperature and the air temperature is very great. 

 There is, as shown in figures 50 to 52, on the whole a very good 

 agreement of the curve W-L with the curve B, particularly for 

 February, but partially also for the average of January and February.* 



Consequently the wind must be regarded as the principal direct 

 cause of the observed variations in the winter temperature of the 

 surface of the ocean. At times for example when the wind blows 

 more continuously than usual from the northern directions of the 

 compass, it leads in the first place to colder masses of air being 

 driven southward and consequently the air temperature falls 

 sharply. Later the colder water layers are driven by the wind into 

 the fields covered bv our observations. 



* Notice that in our figures the curves for surface temperature minus air 

 temperature are inverted. 



