Inferior Mirage (hot road)
On hot roads the air density drops sharply near the surface, so the refractive index n(y) increases with height y. In a horizontally stratified model, n(y) sin θ is conserved along a ray, so light from the sky can curve upward into an observer’s line of sight, creating a bright “wet” patch that is really a distorted image of the sky — an inferior mirage. The simulator traces rays through a linear n(y) profile above the asphalt and draws a simple layered background. It is not a full computational fluid dynamics or radiative transfer model; mirages also occur with temperature inversions (superior mirages) which are not shown here. The goal is to connect gradients in index to ray curvature qualitatively and to motivate why grazing sight lines are most affected.
Who it's for: Introductory geometric optics and atmospheric physics students learning that Snell’s law in layers explains curved rays without “new physics.”
Key terms
- Inferior mirage
- Refraction
- Atmospheric gradient
- Refractive index
- Ray bending
- Sky light
- Stratified medium
- n sin θ invariant
How it works
Inferior mirage: a strong temperature gradient above hot asphalt lowers refractive index with height so light can bend and bring sky light to the eye along the road.
Frequently asked questions
- Is this the same as looming or superior mirages?
- No. Superior mirages happen when cooler air sits under warmer air (inversion), bending rays downward so objects appear elevated. Here the hot surface creates the opposite gradient class, producing inferior mirages.
- Why does the model use n sin θ = const?
- For horizontal layers Snell’s law applied infinitesimally implies that quantity stays fixed along the path — the continuous analogue of discrete layer Snell stepping.
- Can I get quantitative deflection angles for a real highway?
- You would need measured temperature and density profiles. This page uses a tunable gradient for illustration, not meteorological data.
- Does turbulence matter?
- Yes in practice: shimmering near hot surfaces comes from time-varying pockets of air. The simulator uses a smooth profile only.
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