OZ CONSTRUCTION OF ISOBARIC CHARTS 



I shall then draw auxiliary charts that show the differences of pressure for any 

 vertical line between sealevel and the higher levels ; by a simple graphic superposition 

 of these charts upon the isobaric charts drawn in the ordinary way for sealevel we 

 shall obtain the isobaric charts for the various higher levels. It is necessary to pro- 

 ceed in this way in the construction because the kite and balloon stations are too far 

 apart from each other to allow us to draw the upper isobars directly from the results 

 obtained from the ascensions. On the other hand these kite and balloon results suffice 

 quite well for drawing the charts of differences, because the differences change but 

 little from place to place. 



Furthermore, Bjerknes' theory leads to the construction of yet another kind of 

 charts, namely those which represent the lines of intersection of any given isobaric 

 surface with the level surfaces of gravity, and which are thus a kind of topographic 

 charts of the different isobaric surfaces. These charts, which are closely related to the 

 isobaric maps, are like tliose constructed by the superposition of difference-charts based 

 on the observations made at fixed meteorological stations combined with those made 

 by means of kites and balloons. 



If the isobaric chart for any level not too far removed from sealevel is compared 

 with the chart of isobars at sealevel, both charts will be found to show nearly the 

 same type of isobars, and one can scarcely learn more from both together than from 

 the chart for sealevel alone. In such a case, however, the difference-chart furnishes a 

 much more effective means of discovering the relation between these two isobaric 

 charts. Now it has been found that such difference-charts are very closely related to 

 the Bjerknes' solenoids, so that indeed, the number and positions of the solenoids in 

 the atmosphere are fully presented by these difference-charts. I shall therefore in this 

 essay consider equally the difference-charts, the isobaric maps, and the topographic 

 charts of isobaric surfaces. 



I shall first construct the level surfaces of gravity in the atmosphere and then 

 calculate the mutual positions of the isobaric surfaces and the level surfaces of gravity 

 under both static and dynamic conditions. Thus all the aids necessary for the con- 

 struction of the above-mentioned maps will be obtained. Finally I shall show how 

 Bjerknes' theory is to be applied to these charts. 



I would express my warmest thanks to the United States Weather Bureau for the 

 abundant observational data so kindly sent me. I also owe many thanks to Professor 

 V. Bjerknes for his interest and many good suggestions and the support which he has 

 given me during the progress of my work. 



