TRANSACTIONS OF SECTION A. 421 
‘The average wind velocities for the two years are :— 
Height Sod | 5001, | 760 | 1000 | 1250 | 1500 | 1750 | 2000 
Velocitymps. .| 50 | 85 | 110 | 118 | 127 | 129 | 13°5 | 13°6 
Seasonal Variation.—The wind velocity at all levels is slightly greater in 
winter than in summer, the average velocities for the two seasons for successive 
250 m. above m.s.]. being as follows :— 
Ground 
oie) | SRE SOON b> 750 | 1000 | 1250 | 1500 | 1750 | 2000 | 
| Soot Sb | 
| 
Winter . . . 5-2 90 | 11°6 | 125 | 128 | 136 | 13-9 | 13-9 
Summer . | 4-7 81 | 10-4 | 11:2 | 120 | 12-4 | 13-3 | 13°3 | 
Average monthly wind velocities have been calculated, but neither maximum 
nor minimum value of the velocity is sharply defined at any particular month. 
Variation of Wind Velocity with High and Low Barometer.—Both in winter 
and summer the ground wind velocity is greater and the increase with height 
more rapid under cyclonic than anticyclonic conditions. The average wind veloci- 
ties for barometer above and below 760 mm. respectively are as follows :— 
| ) = ] 
| Barometer ae | 500 | 750 | 1000 | 1250 | 1500 | 1750 | 2000 
Above 760. . 43 77 | 9°99 | 10-7 | 11-6 | 11-9 | 12°8 | 12°8 
Below 760 57 9°6 | 12:3 | 13-1 | 13-9 | 14-2 | 145 | 14-6 
Variation of Wind Velocity with Direction of Ground Wind.—For all values 
of the ground wind velocity the rate of increase for S.E., E. and N.E. winds is 
rauch less rapid than for winds from other directions. For example, the average 
velocities under the two conditions are, for ground winds between 4 and 6 m.p.s. 
Direction of Wind Ground | 500 | 750 1000 | 1250 | 1500 | 1750 | 2000 
6 Ew NE. . 48 | 88 | 11°6 | 12-4 | 12-4 | 12:3 | 12:8 | 12°3 
N., -N.W., W., 
SS: (Ke: 4:8 92 | 123 | 135 | 14:1 | 149 | 15°3 | 15°8 
Variation of the Upper Wind with Ground Wind Velocity.—The increase of 
wind velocity with height appears to be additive, and does not vary with the 
velocity at the ground level. 
Variation of Wind Velocity with Time Rate of Change of Barometer.—The 
wind velocity at all heights is great when the barometer is rising or falling 
quickly, but apparently does not depend on the sign of the change. The effect 
is more marked in winter than in summer. 
- Rotation of Wind Direction with Height.—Generally speaking, the wind 
rotates in a clockwise direction with height—i.e., a S. wind becomes more 
westerly, a W. wind more northerly, at the higher levels. This rotation is a 
maximum for 8. and a minimum for N. winds, the average total rotation 
measured clockwise in degrees being at 2,000 m. as follows : For N. ground winds, 
2°-6, E. winds 14°-5, S. winds 289-1, W. winds 12°:8. 
Tables were included giving the variation of wind rotation with direction, 
season, and height above m.s.l. 
Agreement of Observed Wind Velocity and Direction with the ‘ Gradient 
Wind’ as calculated from the formula G = 2wo V sin ¢ and corrected for curva- 
ture of the isobars, the direction being taken as parallel to the isobars. 
