VERTICAL DISTRIBUTION OF THE REFRACTIVE INDEX 



221 



-2700 -2500 



DISTANCE FROM FRONT IN KILOMETERS 

 Figure 5.58. Epoch chart, Glasgow, Mont., in A units. 



air of characteristically low A value. The time cross section for Lake 

 Charles, La. (fig. 5.57), is complex but represents again the same general 

 features: high A values ahead of the front and low ones behind. 



The exponential correction to the refractive index height distribution 

 used in this storm series allows air mass properties to be clearly seen. By 

 use of such an exponential correction, one may construct an idealized 

 refractive index field about a frontal transition zone that shows the tem- 

 perature and humidity contrasts of the different air masses. Further, 

 when this technique is applied to the analysis of a synoptic tropospheric 

 disturbance, it does indeed highlight air mass differences. 



The time cross section presentation is referred to as an epoch chart 

 when the observations are presented as plus or minus time deviations with 

 respect to the frontal passage. Thus, as a frontal system advances and 

 passes over a station, one obtains yet another perspective of the space 

 cross section. Such a presentation is given on figures 5.58 to 5.64. 

 Figure 5.59 represents a typical continental station located in the polar 



