Blue Flash - California

Last updated on September 16, 2023

Blue Flash - California: Exploring a Phenomenal Atmospheric Optics Event

Have you ever witnessed a breathtaking blue flash during a sunset in California? If not, let me take you on a journey to discover the wonders of this rare and captivating atmospheric optics event. The blue flash is a type of green/blue flash that occurs just as the last sliver of the sun sinks below the horizon, creating a brilliant burst of color that lasts for a second or so.

Unlike other flash types that occur above the horizon and are more commonly photographed, the blue flash is harder to observe with the naked eye. However, its brilliance and longevity make it a truly remarkable spectacle.

The occurrence of a blue flash is preceded by several minutes of captivating events. As the sun's disk slowly descends towards the ocean, a second sun appears to rise from the waves. This phenomenon, known as a mirage, creates an "Omega" shape as the two suns meet and gradually overlap. These early signs serve as a preamble to the impending blue flash.

The conditions for a blue flash to occur are set when the last trace of the two suns reaches the horizon. At this point, a particular zone of the mirage experiences significant vertical magnification, bringing the very slight green or blue rim of the sun into focus. This rim, resulting from the differential refraction of green and red rays by the atmosphere, is then considerably magnified, making it easily visible as the "flash."

Technically speaking, the classical flash is an "inferior" mirage, characterized by an inverted image of the sun beneath the "real" one. This effect is similar to mirages observed on hot road surfaces or in desert environments. To create the mirage and subsequent flash, a layer of warm air beneath cooler air is necessary, often provided by contact with a sun-warmed ocean.

While green flashes are more common than blue flashes, the rarity of the latter adds to their allure. But why aren't all flashes blue? The reddening of sunset rays occurs because shorter wavelength rays are scattered away by the atmosphere. Therefore, a particularly clear atmosphere is needed to preserve enough blue in the direct rays. Surprisingly, cloudless skies are not a requisite for witnessing this extraordinary phenomenon.

In conclusion, experiencing a blue flash during a California sunset is an awe-inspiring event that only a fortunate few have had the privilege to witness. The dance of mirages and the magnification of the sun's rim create a brief burst of vibrant blue, leaving observers in awe of nature's wonders. So, next time you find yourself gazing at a picturesque California sunset, keep an eye out for the early signs of a blue flash and prepare to be mesmerized by this extraordinary atmospheric optics event.

Key Points:

• Blue flashes are a type of green/blue flash that occurs just as the last sliver of the sun sinks below the horizon.
• The blue flash is harder to observe with the naked eye compared to other flash types.
• The occurrence of a blue flash is preceded by several minutes of captivating events, including the appearance of a second sun rising from the waves.
• A particular zone of the mirage experiences vertical magnification, making the slight green or blue rim of the sun easily visible as the "flash."
• The blue flash is technically an "inferior" mirage with an inverted image of the sun beneath the "real" one.
• A layer of warm air beneath cooler air, often provided by a sun-warmed ocean, is necessary for the mirage and flash to occur.
• Green flashes are more common than blue flashes due to the scattering of shorter wavelength rays by the atmosphere.
• A clear atmosphere is needed for sufficient blue to be preserved in the direct rays, but cloudless skies are not always required.
• Experiencing a blue flash during a California sunset is a rare and mesmerizing event that leaves observers in awe of nature's wonders.
• Keep an eye out for the early signs of a blue flash during a California sunset to increase your chances of witnessing this extraordinary phenomenon.

Blue Flash

Seen by Jim Grant in Southern California December 30, '09. "We had kind of broken skies tonight. So this GF really surprised me". Images�Jim Grant, shown with permission.

This is a classical green/blue flash, the type where there is a brilliantly coloured flash for a second or so just as the last sliver of sun sinks below the horizon.

Other flash types are above the horizon on the top of a still visible part of a distorted sun. These latter flashes are more often photographed but are less brlliant and long-lived. They are hard to see with the unaided eye.

The events presaging a classical flash become evident several minutes earlier. The sun�s disk sinks slowly towards the ocean but then, before it reaches it, a second sun starts to rise up from the waves. A mirage has started. The two suns soon meet to form an �Omega� shape. Then they overlap more and more.

Finally, as the last trace of the two suns reaches the horizon, conditions are right for the flash. A particular zone of the mirage has considerable vertical magnification and this is now close to the horizon. The very slight green or blue rim of the sun resulting from the ordinary different refraction of green and red rays by the atmosphere is considerably magnified. It becomes easily visible � the �flash�.

Without the preamble of the omega mirage a flash is unlikely to be seen. Look for the early signs when flash hunting.

Technically, the classical flash is an 'inferior' mirage � in the early stages there is an inverted image of the sun beneath the �real� one. The effect is similar to the mirage seen in a hot road surface or in the desert and the air conditions are the same. The mirage and flash requires a layer of warm air (usually provided from contact with a sun-warmed ocean) beneath cooler air.

Blue flashes are a rare compared with green ones. Why are not all flashes blue? Sunset rays are reddened because shorter wavelength rays are preferentially scattered away by the atmosphere. A particularly clear atmosphere is needed for sufficient blue to be preserved in the direct rays. However, these images demonstrate that cloudless skies are not a requisite.

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