

G. I. TAYLOR ON EDDY MOTION IN THE ATMOSPHERE. 7 



ascent, 8 p.m., August 4th. It appears, therefore, that the cooling had extended 

 upwards through a height of 370 metres in 36 hours. An arrow has been drawn on 

 the base line to represent the temperature of the sea which, as we should expect, is 

 slightly less than the temperature of the air which is being cooled by it. The portion 

 of the temperature curve of fig. 2 which lies between 370 metres and 770 metres is 

 due to the warming which the air had undergone between the evening of July 30th 

 and 8 a.m., August 3rd. The portion of the curve above 770 metres to which the 

 warming of July 30th to August 3rd had not yet reached, is due to the cooling which 

 the air experienced as it blew off the warm land of Canada on to the cold Arctic water 

 which runs down the coast of Labrador. 



The curve on the left hand of fig. 2 represents the humidity of the atmosphere at 

 different heights. It is reproduced here for two reasons, firstly, the extreme dryness of 

 the air at 1100 metres (the humidity being only 20 per cent.) shows that the air really 

 had blown off the land as is shown on the chart in fig. 1 ; and, secondly, because it 

 shows that changes in the amount of water vapour in the atmosphere are propagated 

 upwards in the same way as changes in temperature. Bends in the humidity curve 

 occur at the same heights as bends in the temperature curve. This is in fact to be 

 expected, for it is evident that the reasoning which was used to deduce the equation 



(l) would serve equally well to deduce an equation ( - -r-jfor the propagation 



ct jj CZ 



of water vapour into the atmosphere. 



Temperature-height curves, similar to that shown in fig. 2, were traced for all the 

 kite ascents which were made from the " Scotia," and most of them did have bends in 

 them. In all cases in which it was possible to trace the air's path a bend in the curve 

 was found to correspond, either to a change from heating to cooling (or rice ro-sd) of 

 the surface air as it moved along its path, or to a sudden change in the rate of cooling 

 when the air crossed the sharply defined edge of the Gulf Stream. 



In most cases the change from heating to cooling was due to a change in the 

 direction of the wind. Changes in wind direction occur simultaneously over large 

 areas of the ocean, hence, even if the exact position of the path is not accurately 

 determined, we may be able to obtain reliable information as to the time at which 

 heating ceased and cooling began ; and calculations which depend on the interval 

 between the time of this change and the time of the kite ascent will be more accurate 

 than those which involve the length or position of the path. 



Let us consider the temperature distribution in the atmosphere in an ideal case so 

 chosen as to represent as nearly as possible the actual conditions of some of the 

 "Scotia" kite ascents. 



Suppose that the initial potential temperature of the atmosphere is taken to be 

 zero at all heights, and suppose that the surface layers begin to l>e cooled at time 

 t = in such a way that the potential temperature 6 a at the ground, 2 = 0, is a 

 function <j> (t) of the time, so that = <j> (t). 



