Meteorologist captures rare ‘green flash’ in Half Moon Bay


Bay Area Meteorologist Jan Nil has been trying to see the so-called green flash for almost 50 years, looking for a hint of emerald any time it was at a beach during sunset.

But it wasn’t until Null moved to Half Moon Bay a year and a half ago, he made frequent trips at sunset to the beach that he finally caught a glimpse of the phenomenon. Once he knew what to look for, he saw it again and again.

“It actually happens fairly regularly,” said Null, who worked for the National Weather Service’s Bay Area office for more than 24 years before launching his consulting firm, Golden Weather Service Service. “I’d say half the time I go outside with pictures of the sunset, I see some of that green above the setting sun.”

Last week, Null spotted the biggest green flash she saw again and posted the image of Twitter, catching the eyes of many people on social media.


“Mondo Green Flash,” Null wrote. “From last night, this is the biggest example of the Green Flash that I’ve ever photographed plus some cool mock-mirage effects. (The colors are right from the camera with no post-processing).”

An inferior-mirage green flash taken from Mavericks Beach at Pillar Point near Half Moon Bay.

An inferior-mirage green flash is taken at Mavericks Beach in Pillar Point near Half Moon Bay.

Jan Nil

The existence of the green flash has long been debated, especially in Hawaii among tourist groups standing on the condo balconies overlooking the sea. “Look, the green flash,” one person will say. “I didn’t see it!” another will say.

Scientists have established that the green flash is indeed real, and not an optical illusion, though it is only occasionally observed at sunset (most people don’t know what to look for) and even less often at sunrise.

Andy T. Young, an astronomer widely recognized as the world’s leading expert in the green flash, explains about it website dedicated to the phenomenon that two different effects come together to make a green flash that lasts for one to two seconds.


One can explain in a physical lesson the refraction of light. Just as light passing through a scattered prism, light emitted by a flowing sun can be dimmed by the atmosphere, separating different colors.

Each color bends a different amount based on its wavelength; the shorter wavelengths (blue, purple and green) are refracted stronger than the longer ones (yellow, orange and red). Blue and purple lights are scattered in the atmosphere while red, orange and yellow are absorbed, with a vivid green light most visible during the few seconds when the sun sets below or rises above the horizon.

The second is where the atmosphere acts like a lens, enlarging the green hue and creating a mirage.

“When the density profile is curved, the curvature is what produces this lensing (focusing) effect,” Young explained in an email. “A curved density gradient (or, roughly, an error rate that changes with height) produces this effect.”

Flashes can be other colors, too. Young can explain that, in rare cases, on an especially clear day, blue light can make it cross the atmosphere.

There are four different types of green flashes, as indicated above Young’s site, but the two most common are inferior-mirage flash and mock-mirage flash.

The Inferior-Mirage is the classic green flash that’s seen as a thin disc of color as the sun soaks beneath the horizon. This occurs when the water is warmer than the air above and is best seen at sea level.

“This is the kind succinctly described by James P. Joule [an English physicist] as ‘last glimpse’ of the setting sun, “Young wrote in an email.” When the waves are small, you will see this kind of flash is slightly above the sea horizon. “

The mock-mirage is caused by a thermal, most often occurring when the water is colder than the air. The inversion can also be produced by other processes such as the stabilization of air in a high-pressure weather system.

Young explains: “You need to be above the bottom of the inversion to see these well.” “When you’re under the homosexuality, the flashes tend to be skimpy little bumps that are only visible when there’s enough wind shear to make waves on the homosexuality.”

The green flash nile pictured last week from the bluffs at Redondo Beach, about 50 feet above the sea in Half Moon Bay, and sharing on social media was a mocking mirage, as she noted on Twitter.

“The fine structures in the upper part of the picture are small mirages in the upper corner of the sun, probably produced by waves on the homosexuality,” Young said. “These little bits appear to pinch from the top of the disk as the Sun sets, and each one turns green for a second or so before it shrinks to nothing and disappears.”

This would make sense, as Null was photographed on July 8 when Half Moon Bay was very hot and reached high 70s in the afternoon.

“It was a hot night,” Null said. “There was this dry hot layer above the cold water and cold air right above the cool surface. You get a temperature inversion. You get this wavy shape around outside the sun. That’s the light getting ducted to that density they are different in air. You have warmer air and cooler water. The light is coming in different in each layer. “

A photographer captures the green flash at sunset at Poplar Beach in Half Moon Bay.

A photographer captures the green flash at sunset at Poplar Beach in Half Moon Bay.

Jan Nil

Tips on how to see the green flash

A green flash is not always visible, but if you want to see one, it helps to keep these tips in mind.

– Choose a clear day with minimal haze and cloud cover.

– Do not watch the sun until it just sinks below the horizon – your retina may temporarily get bleached because of the bright red light from the sun.

– Choose the right place. Getting straight to the ocean, standing on the beach or on a boat, is best, but looking at a tall building or sea bluff works, too.

-Most green flashes are barely visible and it helps to use binoculars.

-You say that most people don’t know what to look for when they’re looking for the green flash. Li website provide additional tips and advice on how to view it.



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