108 



WIND. 



A glance at the upper diagram in figure 36 wliicli exhibits the total wind from each direc- 

 tion shows at once how insignificant the air motion was from all directions except E., E.S.E. and 



Total Wind 



Whole period 



Feb 1911 -Au|191^ inclysive 



Mean VelociLy 

 whole period 



Vi miles per hour 



Fig. 36. Total wind and mean velocity. 

 S.E. which together had 84-4 per cent, of the total. Of the remaining 12 per cent, (neglecting 

 variable and doubtful) 88 per cent, came from the three directions N.W., N.N.W. and N. 



The mean wind velocity for each direction is shown on the lower diagi-am of figm-e 36. 

 There is little difference in the velocity of the thi'ee noi-therly directions which have any 

 appreciable air motion, but N.N.W. which has the gi-eatest air motion has also the gi-eatest 

 velocity. 



The velocities of the three important winds in the S.E. quadrant are instructive. The 

 E.S.E. direction has the greatest air motion, but the E. has the greatest velocity. This is 

 not only true in the mean, but it was frequently noticed in individual storms. During bliz- 

 zards the wnd vane generally pointed to the E.S.E., the percentage fi-equency in this direc- 

 tion being very much higher than for the directions on either side, but as the wind increased 

 to its most violent effort.s the vane swung slightly to the left and the direction became 

 nearer E. than E.S.E. although it practically never reached due E. On the other hand 

 during lulls the vane swung slightly to the right, so that S.E. and very occasionally S.S.E. 

 directions were recorded. From figure 36 we see that all the directions from S.S.E. to E. 

 have high velocities, but that tie mean velocity increases as the wind becomes more easterly. 

 We shall find the reason for this in our fur-ther discussion. 



The predommance of the winds from the S.E. quadrant was so great tliroughout the year 

 that the resultant direction varied very little from month to month. A good measm-e of the 

 steadiness of the wind direction is given by the ratio of the velocity of the resultant wind 

 to the mean velocity independent of direction. It is obvious that with winds all from the 

 same quarter this ratio would be 1, while if the rnnds were uniformly spread over the whole 

 compass the resultant velocity would be zero and the ratio would fall to nothing. 



