REFRACTIVE INDEX PARAMETERS 



191 



300 400 500 600 



DISTANCE IN KILOMETERS 



Figure 5.14. Idealized warm front in B units. 



various synoptic and air mass effects. The values of bending in the 

 average atmosphere are tabulated [39] and approximate methods of calcu- 

 lating the integral term in (5.11) to within a few percent have been given 

 [40]. 



The next logical step is to plot the frontal cross sections, previously 

 analyzed in terms of A^ and B, in A units. This has been done on figures 

 5.15 and 5.16. The range of refractivity values on the new charts is re- 

 duced from more than 60 to about 25 units and a pattern emerges that 

 displays sharp contrasts for air mass differences associated with the 

 frontal zone. Note, for the warm front case (fig. 5.16), that the A values 

 increase with height until they reach a maximum associated with the up- 

 gliding warm moist air overriding the frontal surface. The region of 

 precipitation in advance of the front is shown as an area of high surface 

 A^. In the cold-front case (fig. 5.15), the classic push of warm air aloft 

 by the encroaching cold air is evidenced by the "dome" of high A values 

 just before the front. Stratification in the cold air due to inversion 

 effects, although impossible to detect in the A'^ charts, is clearly seen by 

 the use of A unit charts. 



