MR. W. H. DINES ON THE VERTICAL TEMPERATURE 



force acting from C to A is produced by the component of the wind at right-angles to 

 \\ V d C being any point* whatever on the same level, although we cannot say 

 produces thi; 2l Thi. comport is called the gradient wind, if it has the 

 5Ll velocity. Also it is found that at a height of 500 metres the 

 wind agrees well, on the average, with that observed by m, ; ms o 



pilot balloons. 



Suggested C*> "f '/"' />/*/, v7,,,,/,m </ Temperature in Cyclone and Anticyclone. 

 To return to the diagram, fig. 2. Let us take a point C on the* left hand at a 

 height of 9 or 10 km., and a point A at the same level on the right, and suppose that 

 a powerful wind is blowing across the line CA, i.e., perpendicularly to the paper. 

 This produces a force acting from C to A, and hence a decrease of pressure at C and 

 an increase at A. The air therefore tries to flow back from A to C. The direct path 

 and neighbouring paths on the same level are blocked by the acting force and a 

 circuitous path has to be followed. Let us take a path ABDC falling vertically from 

 A to 1 km., there running along an isobaric surface to the vertical through C, and 

 then rising to C. The air from A falls towards B and is thereby warmed adiabati- 

 cally, the air from B goes towards D and is unchanged in temperature excepting near 

 the point B, where the supply has come from above. In the part DC the air is cooled 

 as it ascends, and thus we get the temperature distribution shown in the diagram. 

 It is obvious that this distribution at once raises a force that stops the flow, for the 

 air in DC soon becomes too cold to rise further, and that in AB too warm to sink. 

 The path BD need not be straight, but may follow any track whatever in the isobaric 

 surface, neither need AB and DC be vertical. It will be seen, too, that the amount 

 of circulation is very small. The air falls in AB and rises in DC until its departure 

 from the mean is, say, 5 C. The average gradient is 7 C. per kilometre, and the 

 adiabatic for dry air is 10 C., a displacement therefore of only if km. is required, and 

 this in a track of at least 1000 km. length is inappreciable. Each possible path of 

 this kind will, so to speak, be tried and blocked by the air in its attempt to pass from 

 A to C, and the temperature below A will be raised and that below C lowered. As 

 the temperature in the two vertical legs gradually approximates to its average value, 

 under the slow process of in-and-out radiation, the path will be opened again, but 

 only to be rapidly closed by the same means as before, still in this way a slow 

 circulation can occur. 



Exactly similar conclusions apply if we take a path which first rises from A and 

 then falls back to C, but here the low temperatures are found on the right of the 

 diagram and the high on the left. Thus we see that if it be first granted that there 

 is some force acting from any point C to another point A on the same level sufficient 

 to maintain a difference of pressure between A and C, notwithstanding a small but 

 appreciable flow of air across, and further that the line integral of the force for every 

 level path from A to C is the same, but greater than on neighbouring levels, then the 



