Have you ever witnessed a mesmerizing green flash just as the sun sets on the horizon? This captivating optical phenomenon, known as an inferior mirage green flash, occurs when warm air above the ocean causes the sun's rays to be reflected upwards, creating an inverted image of the sun beneath the actual one. While this phenomenon has been observed for centuries, its detailed explanation continues to fascinate scientists and enthusiasts alike.
To understand the mechanics behind an inferior mirage green flash, we must delve into the concept of inferior mirages. These mirages are formed due to a rapid change in air temperature gradient near the ocean or Earth's surface. As the sun's rays pass through the boundary between cool and warm layers of air, refraction causes them to bend upwards. This bending occurs because refraction tends to deflect rays towards the denser layer of air. Consequently, an observer situated above this layer witnesses two solar images: an erect image from rays that pass relatively undisturbed above the warm layer, and a lower inverted image from rays reflected upwards by the warm layer.
As the sun sets, these two images gradually converge, eventually overlapping to form a distinctive "omega" shape. However, it is during a later stage of sunset that the magic of a green flash unfolds. The deflection caused by the warm layer and cooler air boundary becomes extremely sensitive to the angle of incidence of the sun's rays. Even small deviations in this angle are vertically magnified, including the difference in deflection between red and green rays. This amplification provides the necessary separation between green and red that refraction through a normal atmosphere cannot achieve.
The appearance of a green flash is truly a sight to behold. As the sun approaches the horizon, a patch of pure green emerges for a fleeting moment just above its upper rim. This green flash is a result of the vertical magnification of small differences in the angles of red and green rays. The diagram illustrating this phenomenon may exaggerate the curvature of the rays and the vertical scale, but it serves as a visual aid to comprehend the intricate workings behind the green flash.
If you're eager to explore this captivating atmospheric optics phenomenon further, Andrew T. Young's website offers a comprehensive explanation, complete with accurate mirage ray paths and an animated simulation. With these resources, you can delve deeper into the complexities of inferior mirage green flashes and gain a deeper appreciation for the natural wonders that grace our skies.
In conclusion, inferior mirage green flashes are a remarkable optical phenomenon that occurs during sunset. They are the result of warm air near the ocean or Earth's surface causing the sun's rays to bend upwards, creating an inverted image of the sun beneath the real one. As the sun sets, these images merge to form an "omega" shape, and during a later stage, the deflection of the rays becomes sensitive to the angle of incidence, resulting in a distinct green flash. While the phenomenon may seem elusive, it continues to captivate both scientists and observers, providing us with a glimpse into the awe-inspiring beauty of our natural world.
Warn air immediately above the ocean causes the sun's rays to be mirrored back upwards. The rays produce an inverted sun beneath the 'real' one. When the sun has almost set the mirroring becomes very sensitive to the angle of the rays. Small differences between the angles of red and green rays are vertically magnified. A patch of almost pure green is seen - a green flash. The diagram greatly exaggerates the ray curvatures and vertical scale.
Inferior mirages are produced by warm air at the ocean or earth's surface and an air temperature gradient changing rapidly with height. Rays from a low sun are refracted back upwards as they pass between the cool and warm layers. Refraction always tends to deflect rays towards the denser layer. An observer above the layer sees two solar images or parts of them (1) an erect image from rays that pass relatively undeflected above the warm layer and (2) a lower inverted image from rays mirrorred upwards by the warm layer. Each sun image is as 'real' as the other. The effect is not dissimilar to the mirage seen above a hot road surface.
As the sunset proceeds the upper and lower images approach, touch and eventually overlap to form an 'omega' shaped sun.
A green flash occurs because at a later stage the deflection by the warm layer/cooler air boundary becomes very sensitive to the angle of incidence of the sun's rays. Small deviations are vertically magnified including the difference in deflection between red and green rays. This amplification provides the separation between green and red that refraction through a normal atmosphere cannot accomplish.
Andrew T. Young's site has a fuller explanation, accurate mirage ray paths and an animated simulation.
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"Inferior Mirage Green Flash". Atmospheric Optics. Accessed on December 10, 2023. https://atoptics.co.uk/blog/inferior-mirage-green-flash-2/.
"Inferior Mirage Green Flash". Atmospheric Optics, https://atoptics.co.uk/blog/inferior-mirage-green-flash-2/. Accessed 10 December, 2023
Inferior Mirage Green Flash. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/inferior-mirage-green-flash-2/.