Kuumailmiö

Kuumailmiö is a Finnish term that translates to "hot air phenomenon" and refers to a visual distortion of objects seen at a distance, typically occurring on warm days over hot surfaces such as asphalt or sand. It is a type of atmospheric refraction caused by variations in air density due to temperature differences. Sunlight heats the surface, which in turn heats the layer of air immediately above it. This hot air is less dense than the cooler air above it, creating a boundary where light rays bend.

When light from a distant object, such as a car or a building, passes through these layers of air with different densities, it is refracted. The bending of light makes the object appear to shimmer or waver. On roads, this phenomenon often creates the illusion of a puddle of water, as the light from the sky is reflected and bent towards the observer's eyes, mimicking the appearance of a wet surface. This is why it is sometimes referred to as "road mirage."

Kuumailmiö is most commonly observed during summer months when ambient temperatures are high and surfaces absorb significant amounts of solar radiation. The effect is more pronounced when looking across large, flat, dark-colored surfaces that heat up considerably. While it is a common and harmless optical illusion, it can sometimes be a distraction for drivers.