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Novaya Zemlya Effect

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Article Information
Category: Weather Weather
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary
WX
Tag(s) Atmosphere

Description

The Novaya Zemlya effect is a polar mirage caused by high refraction of sunlight between atmospheric thermal layers. The Novaya Zemlya effect will give the impression that the sun is rising earlier than it actually should (astronomically speaking), and depending on the meteorological situation, the effect will present the Sun as a line or a square (which is sometimes referred to as the "rectangular sun"), made up of flattened hourglass shapes.

Atmospheric refraction

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.

"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. " - Excerpt from 'Farthest North', F Nansen 1897.

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