Göran Strand (web) saw this distorted mountain landscape on 16th December at Östersund, Sweden.
The ground cooled overnight by radiating its heat to space. Cold earth then cooled touching air. Morn brought a layered atmosphere, cold air 'neath warmer. Light weaving across the layers refracted. The mountain distorted, a superior mirage and even perhaps a touch of Fata Morgana.
Image ©Göran Strand, shown with permission
Light rays curve towards the denser medium.
Warm air layered beneath denser cold air.
Rays refract upwards. Light source appears lower. In extremis an inverted inferior mirage forms
Cold dense air beneath warmer and lighter air. Temperature inversion.
Light rays refract downwards. Source of light appears raised. In extremis an inverted superior mirage forms.