4 G. I. TAYLOR ON EDDY MOTION IN THE ATMOSPHEEE. 



vertical velocity of the air in places where it is moving upwards. The divisor 2 

 is inserted because the air at any given point is equally likely to be in any portion 

 of the path of an eddy, so that the average value of z-z should be approximately 

 equal to \ (d). 



The equation for the propagation of heat by means of eddies may now be written 



30 wclfrf) 



The equation for the propagation of heat in a solid of coefficient of conductivity 

 specific heat a- and density p is 



(U pa- z- 



It appears therefore that potential temperature is transmitted upwards through the 

 atmosphere by means of eddies in the same way that temperature is transmitted in 

 a solid of conductivity K, provided K /pv = ^wd. We shall in future call K the " eddy 

 conductivity " of the atmosphere. 



If we know the temperature distribution at any time (say t = 0), and if we know 

 the subsequent changes of temperature at the base of the atmosphere we can calculate, 

 on the assumption of a uniform value for K/pcr, the temperature distribution at any 

 subsequent time. Conversely, if the temperature distribution on two occasions be 

 known, and if we know the temperature of the base of the atmosphere at all inter- 

 mediate times, we can obtain some information about the coefficient of eddy 

 conductivity, and hence about the eddies themselves. 



I was fortunate enough to be able to obtain the necessary data on board the 

 ice-scout ship "Scotia" in the North Atlantic last year. On several occasions 

 the distribution of temperature in height was determined by means of kites. The 

 temperature changes experienced by the lowest layer of the air as it moved up to the 

 position where its temperature distribution was explored by means of a kite, were 

 found in the following way. The path of the air explored in the kite ascent was traced 

 back through successive steps on a chart by means of observations of wind velocity 

 and direction taken on board English, German, and Danish vessels, which happened to 

 be near the position occupied by the air at various times previous to the kite ascent. 

 This method was adopted by SHAW and LEMPFERT in their work on the ' Life 

 History of Surface Air Currents.' It depends for success on being able to obtain 

 observations in the right spot at the right time. It frequently happens that no such 

 observations are obtainable, and in these cases it is impossible to proceed with the 

 investigation. Owing to this difficulty I was unable to trace the air paths for more 

 than seven of the ascents. 



