METEOROLOGY — THEORY 205 
80 90 i 110 120 130 
80 90 100 110 120 130 
10 20 30 40. so 
7o tf) 90 loo. "oO 120 130 
19 20 30 40 so 
80 90 ‘00 UT) 120 130 
NAUTICAL MILES 
Ficure 8. Isopleths—refractive index [ (~=1) 108], 
ing the magnitude and height of the strong gradients 
along the path. The time interval of each sounding is 
shown on the appropriate section. 
Again it must be emphasized that the discontinuity 
takes the shape of a warped surface, that the gradi- 
ents vary from point to point, and that the maximum 
air density change occurs in the region of maximum 
refractive index gradient. Interface waves in the 
density discontinuity are possibly superimposed on 
the already nonuniform structure. These small inter- 
face waves are evident by the undulations on the top 
surface of the stratus cloud deck. The top surface of 
the cloud deck, which is often present, marks the air 
mass boundary and is thus a good indicator of the 
base of the inversion. 
It is therefore evident that meteorological observa- 
tions required for a thorough study of propagation 
conditions must be as extensive as possible. 
