I02 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



If at one place a strong wind occurs and thereby stronger surface 

 currents are produced without a corresponding increase in the cur- 

 rents in the region behind, then an increased transportation of the 

 surface water must be in part made up by water taken from the 

 underlying layers. If this is colder, then the surface temperature 

 must sink thereby, even if the wind itself comes from warmer 

 layers of the ocean. This in many cases occurs suddenly by reason 

 of local winds, without continuing long enough to appear in the 

 monthly means. 



The above mentioned exceptions to the general rule concerning 

 the action of the wind on the surface temperature of the ocean are 

 those which must be expected to make themselves least felt in the 

 North Atlantic Ocean in the months of the year which are included in 

 our investigations. The surface of the ocean is then most cooled and 

 the convection streams are in the greatest degree of homogeneity 

 in a vertical direction. 



When the sun begins to warm the ocean surface in the spring, 

 it would be otherwise and it may then be understood, how, as we 

 shall later describe, the best agreement between the wind relations 

 and the variations of the surface temperature is found in February. 



COMPUTATION OF AIR PRESSURE GRADIENTS AND WIND DIRECTION 



The process employed by Meinardus of determining the air pres- 

 sure difference between some few chosen places does not serve to 

 exhibit clearly the influence of the air pressure distribution and the 

 winds which arise from it on the observed variations in the surface 

 temperature of the ocean. To be sure, one obtains in this way a 

 kind of sample of the variations in the strength of the atmospheric 

 circulation, but the process does not give us the variations in the 

 direction of the circulation in the different regions, and this is 

 exactly what it is necessary to know. 



We have found that an investigation of the air pressure distribu- 

 tion (and the wind relations depending thereon) may be obtained 

 most conveniently for our purpose with the help of the monthly 

 charts of the air pressure distribution of the Atlantic Ocean, which 

 are based on the daily synoptic weather charts published by the Dan- 

 ish Meteorological Institute and the Deutschen Seewarte. Publica- 

 tions of this kind are available for the years 1898 to 1908. Before 

 the printing of this memoir we obtained, through the kind assistance 

 of Mr. Ryders, Director of the Danish jNIeteorological Institute, 

 ])roof-sheets of the isobar charts for January, February, and March, 

 1909 and 1910. 



