A Mirage is an optical illusion that can be sometimes observed on hot days. When air near ground level is heated strongly by contact with the hot ground, it becomes less dense. This is because the air near the heated ground becomes considerably hotter than the air above, causing refraction of light rays from the sky, since the refractive index of air depends on its density and therefore on its temperature. As a result, the relationship between objects and the horizon becomes distorted. In fact often a patch of sky is mirrored in the hot air giving the shimmering appearance of a pool of water, where there is none.

There are two main formes of mirage, classed according to whether the image of a distant object appears lower or higher that would normally expected. An inferior mirage occurs when the ground surface is strongly heated and the air near the ground is much warmer than the air above. Everyone might know the this of mirage where pools of water appear to be lying on a hot road.

In a superior mirage, the opposite conditions occur: the air close to the ground surface is much colder than the air above, which is known as temperature inversion. Light is bent downwards from the object towards the viewer so that it appears to be elevated or floating in the air. Superior mirages are less frequent than inferior ones and a more common over larger water bodies, which are sometimes much colder than the air above it, e.g. in spring. Superior mirages are also frequent in high-latitude regions, such as Island and over glaciers.

A famous superior mirage is the Fata Morgana , most frequently seen in the Strait of Messina between Italy and Sicily. However, Fata Morgana's are also frequent in deserts, after night time radiation has cooled down the sand to temperatures lower than the air above. Distant objects appear extremely elongated, giving the impression of buildings and towns in the distance. This phenomenon is also known as 'castles in the air'.

Add to social bookmarking:  | more |
A is for Air
Accessory clouds
Air masses and their sources
Air-mass Thunderstorm
Alpine Glow
Atmosphere - Diagram
Aurorae - Northern Lights
Average rainfall over England and Wales
Azores High
Banner Cloud - the peak's flag
Beaufort Scale
British Weather Terms
Brocken Spectre
Bubble High
Burning Time
CAPE - Convective Available Potential Energy
Cap cloud
Cc floccus
Cc lacunosus
Cc stratiformis
Cc undulatus
Central England Temperature
Centres of action
Ci fibratus
Ci radiatus
Ci spissatus
Ci uncinus
Ci vertebratus
Clocks go Back from BST to GMT
Cloud classification
Cloud seeding
Cloud species
Cloud streets
Cloud types (genera)
Cloud variety
Clouds - sentry of the sky
Cold low
Comma Cloud
Comma Cloud
Coriolis effect
Crepuscular rays
Cut-off low
Dew Point
Discovery of the Jet Stream
Doppler radar
Drifting snow - blowing snow
Earth's Atmosphere
Easterly wave - the Hurricane's cradle
El Nino
Föhn (foehn) wind
Föhn wall
Flash Flood
Fog and Mist
Forecasting weather
Frost hollow
Fujita Scale Statistics
Fujita Tornado Scale
Funnel cloud
Genoa Low
Geostationary Satellites
Geostrophic Wind
Glaze and Black Ice
Grass Minimum Temperature
Hailstorms in Britain
Highs and Lows and Winds
History of Hurricane Names
Hoar Frost
Isobars on surface maps
Jack Frost
Jet stream cirrus from space
Katabatic winds
Key to our weather symbols
Lake-effect snow
Latent Heat
Levanter cloud
Millibar and hectopascal
NOAA satellites
North Atlantic Drift (Gulf Stream)
Polar Orbiting Satellites
Polar low - the arctic hurricane
Precipitation Map
Rain gauge
Roll cloud
Rotor cloud
Saffir-Simpson scales
Sc duplicatus
Sc perlucidus
Sc undulatus
Shelf Cloud
Sometimes a bit fishy
Southern Oscillation
St. Swithun's Day
Standard Reference Period
Stevenson Screen
Sun pillar
Supercooled clouds
Surface wind
Thunderstorm Probability
Tornado Alley
Troposphere - Diagram
UV Index
Ultraviolet radiation
Virga or Fallstreak
What Makes Northern Lights Happen?
What does it mean?
Why Skies are Blue
Why Thunder Rumbles
World Meteorological Organisation (WMO)