Stockholm Sunset

Imaged by Peter Rosén "I often observe the sunset and have been able to photograph the green flash several times and even the blue flash on one occasion. On the 24th of February I photographed the setting Sun for 13 minutes at a rate of 1 shot every 2 seconds. Although very beautiful, I did not expect anything to happen as the upper rim was very stable and uneventful. But suddenly the lower part started to split in an unexpected way and I expect some thermal inversion layers at work.".   ©Peter RosÚn.
Atmospheric
Optics
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Normal” atmospheric refraction increasingly flattens the sun as it approaches the horizon.    The refraction raises the apparent sun above the true one.   The effect strengthens closer to the horizon so the lower part of the disk is raised most, resulting in an oval shape - from space this is extreme.

Then the sun’s light starts to pass through an inversion layer, abnormally warmer air above cooler.   Sunlight is refracted by the density gradients to give a ‘mock-mirage’.      With a single inversion layer there are three images, an upper erect one, a lower ascending inverted image and a lower descending erect one.    Here the inversion layer is more complex giving more sun slices.

Mock-mirages often give green or ble flashes on the top of the sun. The classical inferior mirage produces a longer and more intense flash close to the horizon.