Optical phenomena in the atmosphere: What physical principle best explains a desert mirage? Consider the shimmering water-like appearance on hot roads or deserts caused by vertical temperature gradients in air. Choose the correct option.

Concept
Near hot surfaces, air is hotter and less dense close to the ground; refractive index decreases with height, creating layers. Light from the sky bends continuously and can undergo effective total internal reflection, reaching the eye from below, mimicking water.

Key idea
Mirage = apparent inverted image due to refraction approaching total internal reflection in a refractive-index gradient.

Final Answer
Total internal reflection in stratified hot air