XXV111 



INTRODUCTION. 



per second = 



2 7T 



, and <$> = latitude. In the Northern Hemisphere the 



86154 



winds gyrate counterclockwise in cyclones and clockwise in anticyclones. 



These gyrations are in the reversed direction each to each in the Southern 



Hemisphere. 



AP 

 In equation (2) the values of V are imaginary for values of — ■ greater 



AP pr 

 >, or r = - - defines and 



AP 



than co 2 sin 2 <j>. The equality = w 2 sin 



pr pco 2 sin 2 



fixes an isobar with minimum curvature in anticyclones. Winds cannot 



flow parallel to the isobars within this critical isobar. For this isobar the 



AP 



gradient wind has its maximum value V c = : . For the same gra- 



pco sin 



dient and for an isobar with the same curvature in a cyclone the gradient 



velocity is V t = V c (V2 - 1) = 0.414 V c . 



When the isobars are parallel straight lines, a condition very often closely 



realized in nature, r = 00 and the gradient winds have the value given by 



either (1) or (2) after squaring, namely, 



V r = „ = V s = — ^— = - V c . 



r s 2 poo sin 4> 2 c 



For practical units equation (1) becomes 



V= R 



V 



V 



— .07292 sin 4> 



068914 sin 2 <}>+ ^~ .26252 sin 



Kpa 



Units of 

 pressure. 



(I) (Millibars) 

 (II) (Millimeters) 

 (III) (Inches) 



V = velocities in meters per second in (I) and (II) and in miles per 



hour in (III). 

 R = radius of curvature of isobar (wind path) in kilometers in (I) and 



(II) and in miles in (III). 

 The gradient is to be deduced from isobars drawn for pressure inter- 

 vals of 1 millibar in (I), I millimeter in (II) and — inch in (III); d, is the 



perpendicular distance between isobars (as above defined)- in kilometers in 



(I) and (II), and in miles in (III). 



p = density of air = grams per cubic centimeter in all cases. 



