The hypothesis is proposed that the vertical gradient of the refractive index is strongly affected by the vertical motion in the atmosphere. It is shown that changes in this gradient are due principally to changes in the moisture stratification and temperature lapse rate resulting from the vertical velocity and its horizontal gradient within the air mass. Mean radio signal strengths are plotted against the time position of 500‐mb troughs and ridges relative to the radio link. A series of 500‐mb charts is given, with the vertical velocity field obtained by the Sawyer‐Bushby method. The vertical velocity over two radio links is compared with the signal strength. Cross‐sections taken through several of the troughs illustrate the stratification changes on the forward and rear sides of the troughs due to vertical motion.
A study is made of meteorological conditions associated with synoptic patterns passing over the Middle West leading to super-refractive index profiles. The signal strength for a 71.75 mc TV-link in Illinois is related to the refractive index profiles.
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