240 THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



The final pressure^, with which the sinking air reaches the ground 

 in the an ti-cy clone, is greater than the initial pressure p a that prevails 

 at the ground within the cyclone, and correspondingly /is higher above 

 the axis of abscissas than a. In this case it may occur that the point/ 

 comes to lie not only (as is self evident) above, but also to the right of «, 

 so that v f y v a or in other words that the air at the base of the anti- 

 cyclone, notwithstanding the higher pressure, is specifically lighter than 

 in the cyclone, because the temperature more than compensates for the 

 influence of the pressure. 



This shows in a very clear manner that in the exchange of air be- 

 tween cyclone and anticyclone we have to do not only with the specific 

 weight of the mass of air, but that here dynamic relations are of first 

 importance, a poiut to which Haun has called attention lately in the 

 discussion of the observations taken on the Sounblick.* It will be well 

 in the more accurate investigation of this question to give increased 

 attention to the processes above the aqueous clouds especially at their 

 upper boundary surfaces. 



As to the relations of the humidity to the processes just considered 

 these are nearly the same as those in the case of the foehn. Here also, 

 that is to say in the anticyclone, the air arrives in the neighborhood 

 of the ground warm and dry, but in the immediate neighborhood of 

 the ground the evaporation stimulated by unrestrained insolation will 

 rapidly add moisture to the air, so that the indicator, which moving from 

 b nearly to e has steadily approached the PV plane and from c on the, 

 way towards /has remained a long time at the level of e, must now be 

 imagined as rising immediately before reaching /. If now the air that 

 has descended in an anticyclone again flows toward a new depression 

 then will it (under the assumption of the same conditions in this as in 

 the first cyclone), by reason of a continuous acquisition of aqueous va- 

 por, pass through conditions that are represented in the diagram (Fig. 

 34) by the line fa. This line we have to imagine as slowly rising, so 

 that the diagram here drawn presents in fact the projection of a closed 

 line. 



(3) The interchange of air between cyclone and anticyclone in winter. 



In winter the diagram for this process of interchange has a figure 

 essentially different from that in Summer. First, all changes in con- 

 dition, at least insofar as concerns the initial and final conditions (see 

 Fig. 35), take place nearer to the coordinate axes since the tempera- 

 tures that come into consideration do not rise so high as in summer, 

 and since, corresponding to this, the isotherms that lie far from the axis 

 are not attained. Again, we have here lower pressure and higher tem- 

 perature at the starting point a, but at the end d higher pressure and 

 lower temp erature, so that d is to be sought to the left and above a. 



* MeteoroloyischeJeitschrift, 1888, vol. v, page 15. 



