Wind velocity is normally recorded at a height of -

Air velocity The air velocity is measured by an instrument called the anemometer. It consists of four hemispherical cups, attached to the ends of 2 crossed metal arms. There is a veical spindle which is attached to the 'anemometer box'. The velocity of the wind is indicated on a counter called the cyclometer, placed in the anemometer box. Wind velocities are normally recorded in open flat country at a height of 10 m. Velocities are measured in metres per second (m/s.). When the wind speed is 0.5 m/s, it is described as complete calm with smoke rising veically; when it is 3.3 m/s, it is described as slight breeze with leaves rustling; when it is 10 m/s, it is described as strong wind with larger branches of trees moving; when it is 15-20 m/s, it is called storm; when it is 25-30 m/s, it is called gale; and over 30-50 m/s, it is called hurricane. KATA THERMOMETER : The Kata thermometer is quite sensitive to slight air movements. 'It can record air velocities as low as 10 feet per minute. Ref : Park 25th edition Pgno : 784