Hafgerðingar and giant waves

Abstract

A 13th-century text in Old Norse, Konungs Skuggsjá (translated as The King's Mirror), tells about a phenomenon that may be encountered in the Greenland Sea. It is called hafgerðingar (sea fences). The horizon is raised, and from there three giant waves come rolling in. Recently Lehn and Schroeder have explained the phenomenon as a superior mirage. I extend their analysis by introducing a periodic time dependence in the properties of the inversion layer, and show that also the illusion of incoming waves and an immediate danger may so be explained.

Novaya Zemlya effect and Fata Morgana. Raytracing in a spherically non-symmetric atmosphere

“…Before extending to spherically non-symmetric atmospheres, I will shortly review the methods that lend themselves to this purpose. Some of the following material has been borrowed from earlier publications on refraction [8][9][10][11][12][13][14][15], and is reused or adapted here with the kind permission of the publishers.…”

“…I have used this hyperbolic form in Ref. [15], which deals with the hafgerdingar mirage. In this reference, the inverse of the diffusiveness was introduced as the steepness.…”

“…In Ref. [15] this was used to bring in the dynamics by which the hafgerdingar mirage might look like three giant waves rolling in, as it is told in the Old Norse myth [3][4][5].…”

“…These have the appearance of a steep wall or a giant wave on the horizon that fences in the sea all around. In reference [15] I have given a simulation of the hafgerdingar and shown that long running surface waves on the top of the inversion layer may create the illusion that these giant waves are actually moving.…”

“…Thus there are at least two different ways, in which a mirage may produce the wall-illusion. There may be more than two: in reference [15], I have given an interpretation of the hafgerdingar as due to a mirage which produces bands of rays that alternatingly hit the sea, or escape to the sky. Quite common is the version where a duct is seen as bounded at its top by just one band that corresponds to the sea, such as in the hafstramb simulation of Figure 11.…”