|Miraged Icebergs at Disco Bay, Greenland Two panoramas by Lars Brubæk. Taken from the motor ship 'Fram' at a height of 15m above sea level. The camera points east towards either Arveprinsens Island or mainland Greenland. Scroll right for the majesty of the berg strewn sea. ©Lars Brubæk, sown with permission.|
|There is much going on over Disco bay. The closer icebergs are not visibly miraged but the more distant scene is a symphony of reflection and distortion.
Above most of the distant bergs floats an inverted image. Above that is yet a third
A temperature inversion is responsible. The icy cold sea cools the air it is in contact with forming an unusually cold layer beneath warmer air. The inversion top is visible as a ragged line against the distant mountains.
Light rays passing between the dense colder air and the upper warm air are refracted. The ray paths become curved and concave to the horizon level. I.e. they tend to curve downward. The curvature is always such that the rays tend to curve towards the cooler - denser - air. The ray curvature is strongest where the vertical temperature gradient is greatest.
At right, the ray 'b' from the real berg top is slightly curved making it appear to originate from a point above. Ray 'c' from the berg's base encounters a higher region of even greater temperature gradient and is more strongly refracted. A rule of thumb is that where ray crossing occurs the resulting image is inverted. An upside down berg floats over the lower one!
Rays from the berg top have a third route 'd' available through upper warmer air before curving down towards the eye or camera. These form a third image - this time the right way up.
|At right, Fata Morgana architectural embellishments create a towering structure.
At left, inverted counterparts float over the bergs.