Conditions

Modified Refractivity Gradient (Units)

Results (Phenomena Will Occur)

Trapping

<0

Trapped: Propagation within the duct boundaries

Super-refraction

0 - 79

Refract downwards towards the Earth’s surface, but at a rate less than the Earth’s curvature but greater than standard

Standard/normal

79 - 157

Refract downwards towards the Earth’s surface with a curvature less than the Earth’s radius

Sub-refraction

>157

Bend upwards, away from the Earth