Atmospheric
Optics
Novaya Zemlya Effect, Antarctica
Not a sunset! A rectangle of glittering golden stripes bejewelled by green flashes lights the icy horizon. The sun had already set several minutes earlier and was well below the horizon. The fabled Novaya Zemlya effect.
A sighting by Markus Wildi at Dome Concordia in the Antarctic at 75.6°S 123°E elevation 10,600ft.
Image ©Markus Wildi, shown with permission
Abnormal atmospheric refraction and miraging are responsible. Under Polar conditions, severe air temperature gradients can exist above the ice surface. When there is a strong temperature inversion layer – colder air below a relatively warmer layer – we have the conditions for a Novaya Zemlya (NZ) mirage.
Rays from the sun can enter the cold layer (see below). Once there they can be channelled (ducted) around the curvature of the Earth for distances up to a few hundred kilometres. A ray passing from cold air into warmer air is always refracted back towards the colder medium. If the refraction is strong enough the ray mirrors up and down inside the duct. An observer at the other end sees a slot shaped image of the below horizon sun transmitted hundreds of miles. A bit like a terrestrial star gate! Several oscillating paths are possible giving the characteristic stacked lines with blackness between. In the fully developed NZ effect each slot shaped image is a squashed full width whole sun thus giving, in total, a rectangular shape.
Polar conditions or the lower warmer air layer are not always necessary and NZs are sometimes seen off the Californian coast where strong inversions result from the combination of cold offshore sea currents and warm air from the land. A weaker form of the NZ is the more familiar mock-mirage of three or more segmented suns.
Thanks to Andrew Young for valuable discussions.
A Novaya Zemlya effect sketched by the famous Arctic explorer, Fridtjof Nansen, on 16th February 1894. He had deliberately set his tiny ship 'Fram' into the ice to drift with it across the Arctic and hopefully to near the North Pole.
"The mirage was at first like a flattened-out glowing red streak of fire on the horizon; later there were two streaks, one above the other, with a dark space between; and from the main-top I could see four, or even five such horizontal lines directly over one another, and all of equal length; as if one could only imagine a square dull-red sun with horizontal dark streaks across it. An astronomical observation we took in the afternoon showed that the sun must in reality have been 2° 22' below the horizon at noon; we cannot expect to see its disk above the ice before Tuesday at the earliest; it depends on the refraction, which is very strong in this cold air. "
From 'Farthest North', F Nansen 1897.
The sun suddenly appears during the long Polar winter several days before it is expected to first show itself in spring. Or, later on, sunrises are unusually early and sunsets late. The "sun" is a flickering rectangular stack of thin pancakes spaced by darkness.
The effect was first recorded in 1597 during one of Barentz’ Arctic expeditions. The ship was beset in ice and the crew wintered on Novaya Zemlya (New Land/Earth). A ‘sunrise’ was seen on January 14th two weeks earlier than calculated and when the sun was actually 4.9° below the horizon. Later, Nansen (account at right) saw it. Ernest Shackleton observed it in Antarctica during his 1914-17 expedition that ended with one of the world’s greatest sea voyages to South Georgia.
