Which term is associated with Warm Dry Air high and Cold Moist air Low?

• A. Elevated Ducting
• B. Diffraction
• C. Sub Refraction
• D. Super Refraction

Answer: (D)

The main idea is how the vertical change in refractive index of the air bends radar waves. Refractivity (which governs how much the wave bends) depends on temperature and humidity; cooler, moister air near the surface has a higher refractive index than warmer, drier air up high. When warm, dry air sits above and cold, moist air lies below, the gradient of refractivity with height becomes steeper than normal. Radio waves bend toward regions of higher refractivity, so they curve downward more than usual, extending the apparent range. This intensified downward bending is known as super refraction. If the gradient were even stronger, it could trap the wave in a duct, but the described setup mainly produces heightened downward bending characteristic of super refraction.