NO. 4 TEMPERATURE VARIATIONS IN THE NORTH ATLANTIC 249 



air pressure difference in the northeast trade winds occurs in the 

 years 1886 to 1887, and again 1889 to 1890 with corresponding fea- 

 tures in the curve of Colombo-Hyderabad. 



THE AIR PRESSURE DIFFERENCES OF THE NORTH ATLANTIC AND 

 THE TEMPERATURE VARIATIONS 



In order to get a closer view of the variations in the dynamics 

 of the atmosphere it is obviously necessary to study the variations 

 between the different action centers instead of only taking air pres- 

 sure differences between some chosen fixed points. It must also 

 be of importance to consider both the variations in the strength of 

 the action centers and the variations in their position at the different 

 times. In the first respect it should be investigated whether the 

 difference between an air pressure maximum and the adjacent air 

 pressure minimum would furnish approximate values for the dis- 

 turbance of the atmosphere. For this purpose we now consider one 

 of the most marked air pressure minimum of all the earth, namely 

 the so-called Icelandic minimum and the adjacent region in the 

 south, the so-called Azores air pressure maximum. Both have the 

 advantage that they have very definite forms. They continue for 

 the whole year, while the continental action centers mostly change 

 from maximum to minimum between winter and summer. 



In order to obtain an entirely satisfactory expression for the 

 atmospheric condition over this part of the earth it would be neces- 

 sary to study not only the difference between the pressure of these 

 two action centers without regard to their position, but also to 

 measure the distance between the centers, that is, the gradients, and 

 the direction and the position of the lines of flow between them. 

 Such an investigation would necessarily be very wide. We hope 

 to undertake it later. Prelyninarily we have confined ourselves to 

 determining the difference of the intensity of pressure in the region 

 of maximum and minimum only for a single month without regard 

 to the variations in the positions. It appears that the air pressure 

 variations in the maximum region are so small that the considerably 

 greater variations in the minimum region would give alone by 

 themselves almost the same result as if one should observe actu- 

 ally the difference between maxima and minima. 



In this investigation we have employed charts of the average 

 air pressure distribution over the Atlantic Ocean for each month 

 which are published by the Meteorological Institute of Copenhagen 

 and the Deutsche Seewarte in Hamburg. From these charts we 



17 



