relating to Rotating Fluid in the Atmosphere. G69 1 



We may regard this line of centres as an axis of the 

 cyclone or anticyclone. In a cyclone, with co small, the axis 

 is very nearly parallel to the axis of rotation of the earth. 

 Corresponding to larger and larger values of co positive, the 

 axis tends more and more towards the vertical line drawn 

 from the centre of isobars. In anticyclonic motion on 

 the other hand, with co small, the axis is very nearly parallel 

 to the axis of rotation of the earth ; and with increasing- 

 values of negative co the axis tends towards the horizontal 

 line drawn due north from the centre of isobars. The 

 greatest admissible value of co negative, according to the 

 above equation, is clearly given by 



^ = 20sin^. (6) 



Thus for an anticyclone the maximum angular velocity 

 at the equator is zero and at the pole it is 2X1. This result 

 would imply that no anticyclonic motion could be observed 

 at the equator; at least no motion of the type under con- 

 sideration in which the motion of each particle is in a 

 horizontal plane. The absence of permanent or semi-per- 

 manent centres of high pressure from the equatorial belt of 

 the earth's surface is in agreement with the theoretical result 

 obtained above, and may be regarded as some confirmation 

 of the idea that in the larger cyclonic and anticyclonic 

 movements horizontal motions predominate. The assumption 

 that the motion is horizontal cannot of course be considered 

 as one likely to be strictly fulfilled in the equatorial region. 



The relation of the upper winds to ground winds at any 

 point of the earth's surface within the area covered by a 

 cyclone or anticyclone can be readily determined for a 

 stationary cyclone or anticyclone from the equations already 

 given. The inclination of the axis of rotation could also 

 readily be determined from observations of the ground wind 

 and upper wands at one or two points within the area. We 

 may take for example tw r o points of observation — A due 

 north of and B due south of 0. At B the upper winds 

 continuously increase in velocity with height above the 

 surface. At A the velocity of wind decreases with height 

 until the axis is reached where the wind velocity is zero. 

 Further increase in height is accompanied by increasing 

 wind velocity in the opposite direction to that of the wind at 

 the ground. If our points of observation do not lie due 

 north or due south from 0, upper wind velocities change in 

 direction and amount with height in a manner depending on 

 the position of the point of observation relative to 0. The 



