Green Flash from the Bohemian Forest

Last updated on September 16, 2023

Green Flash from the Bohemian Forest: A Rare Atmospheric Phenomenon

Have you ever witnessed a green flash during sunset? It's a breathtaking sight that occurs when the last sliver of the sun's disk slips beneath the horizon. But what if I told you that there is an even more rare and captivating version of this phenomenon? Welcome to the world of the "Green Flash from the Bohemian Forest"!

Located in Austria, the Bohemian Forest is known for its stunning natural beauty. On the evening of January 10, 2009, Karl Kaiser, an avid observer of astronomy, biology, and meteorology, captured a remarkable moment. The recent cold weather and widespread temperature inversion created the perfect conditions for a miraged sunset, accompanied by the elusive green flash. In fact, there was even a suspicion of a blue flash, which adds to the intrigue.

To understand this phenomenon, we must first delve into the concept of temperature inversion. Normally, air becomes cooler as you ascend in the atmosphere. However, during a temperature inversion, a layer of cold air forms beneath a layer of warmer air. This inversion causes the sun's rays to refract in unique ways, resulting in intriguing optical effects.

In the case of the Green Flash from the Bohemian Forest, the temperature inversion caused a "mock-mirage." As the setting sun's rays passed through the layers of air, they were split into pancake shapes with green flashes appearing in the uppermost layer. This distinctive splitting and coloration created a mesmerizing display for observers like Karl Kaiser.

The traditional green flash, on the other hand, occurs when warm air lies beneath cooler air. As the sun sets and its disk slips below the horizon, a sliver of green light can be seen for a brief moment. This phenomenon is often observed in coastal regions, where the temperature gradient between land and sea creates the ideal conditions.

Karl Kaiser's images of the setting sun may appear unsharp, but this was actually a result of the "restless" air on that particular day. The strong scintillation, or twinkling, of the air made it challenging to see the upper parts of nearby hills distinctly. However, this atmospheric turbulence played a crucial role in enhancing the visibility of the green color, making it appear more extended and vivid.

The Green Flash from the Bohemian Forest is a rare and captivating event that highlights the beauty and complexity of atmospheric optics. While traditional green flashes are already a sight to behold, this unique phenomenon takes it to a whole new level. It serves as a reminder of how our atmosphere can surprise us with its stunning displays and intricate interactions.

Next time you find yourself gazing at a sunset, keep your eyes peeled for any hints of green or blue flashes. Who knows, you might just witness a rare spectacle like the Green Flash from the Bohemian Forest. Nature has a way of surprising us when we least expect it, and these fleeting moments of beauty are a testament to the wonders that surround us.

Green Flash from the Bohemian Forest, Austria. Observed by Karl Kaiser (Astronomy, biology & meteorology site) on the evening of Jan 10, '09.. ©Karl Kaiser, shown with permission.

The recent cold weather (see hoar frost crystals) and widespread temperature inversion produced moonset mirages and this miraged sunset with accompanying green flash. There is even a suspicion of a more rare blue flash. The inversion, cold air beneath warmer, has refracted the setting sun's rays to give a 'mock-mirage' where, characteristically, the sun is split into pancake shapes with green flashes in the uppermost layer.

The more traditional green flash is seen as the last sliver of disk slips beneath the horizon and is produced by the opposite arrangement of air - warm beneath cooler.

"These images of the setting sun seem to be unsharp - that is as it was. The air on that day was very "restless", the scintillation of the air was very strong. But I think this is reason why the green colour is seen so well, the green parts are extended. It was not possible to see the upper parts of nearby hills distinctly because of the strong scintillation!"

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