WIND, TEMPERATURE AND EVAPORATION 



213 



similar course, but the curve of surface wind flow shows that the 

 early and late portions of the season are windier than midsum- 

 mer. The data for monthly evaporation, average monthly tem- 

 perature, and average hourly wind flow per month for all three 

 seasons are shown in table 1, and the curves for the season of 

 1917 are shown in figure 1. 



It seems obvious that the seasonal distribution of air flow is 

 partly related to the development of vegetation. In the early 



TABLE l> 

 Correlation between air flow and evaporation 



Erap. Air flow — > 



I 00 50 100 150 200 250 300 350 400 450 500 550 GOOFreq. evap. 



months particularly, and in the autumn to a lesser degree, there 

 is little obstruction to air flow from vegetation, but as summer 

 advances this obstruction must offer considerable frictional re- 

 sistance to atmospheric movement. At the same time convec- 

 tion currents are more vigorous in the early and late portions 

 of the season, as these are the periods of rapid and violent tem- 

 perature changes. It is also obvious from figure 1 that the 

 correlation between evaporation and temperature is much closer 

 than between evaporation and air flow. Unfortunately the 



