Orange Bay Area Skies and the Science of Light

Sky above San Francisco was the color of television that the president got.

To be fair, I stole that Punch line The nerd-litn snark from Twitter, and Donald Trump’s apparent choice in his alleged makeup, did not fix climate change and the worst North American fire season on record. There are about 100 fires burning all over the west, blowing through lightning splashes through the electrifying, dry-wooded, beet-eaten forest and chaparral. The flames have so far consumed 3.4 million acres of land, including the entire city and more than 1,000 homes. But none of it tells what happened to Akash. Residents of the Bay Area of ​​California did not think it was fun to wake up on Wednesday morning in the color-stained sky of the Golden Gate Bridge. Street lights did not go off; The large Sutro broadcast antenna poked through the mist like a mechatronic eye of solar; And a temper-magma glow suffered everything, like being caught in just one strip of a spectacular sunset. Disappointed half-jokes about the plagues of darkness, the twilight of the afternoon, and the excitement of the city Blade runner 2049, Westerners were surprised: No, but really, why is the sky that color?

The cause of the orange — and the rays following Van Yello and disease — is a combination of atmospheric chemistry and the physics of tiny things.

And more, the reason, duh, was the fire. Many are so big and so hot that they produce Pyrocumulonimbus cloud, Or “firestorm”, which sends soot and smoke all the way to the atmospheric column, 50,000 feet into the stratosphere. The heat also caused unusual winds that raised smoke from the Sierra Nevadas to the coast. All that gunk literally blocked the Sun. at least, some Sun’s – satanic color was in the description. “I have never seen anything like this. I’ve been to polluted cities, but you never get that dark orange, ominous color, “says Sanaz Wahidinia, a physicist at the NASA Ames Research Center who studies aerosols and light scattering. “Usually in polluted cities, it is tinted in this color, the color of the sepia I see now is probably a little blurred. It was really fascinating. ”

First, towards chemistry. Smoke is that which is released after some burning, the particles are reduced; It can be a hydrocarbon molecule or soot, which is straight black carbon. Now, the thing to remember here is that even though the cover appears almost white or white-yellow in the sunlight, it actually contains approximately equal amounts of each wavelength of light, ranging from the red end of the visible spectrum All mixed up to blue color. In a submetallic pointillist spray — and even if you’re pairing carbon-heavy things like oil or coal with black, there’s a possibility of absorbing light from the visible spectrum — carbon atoms actually have priority. They absorb and disperse more long-wavelength red hues than shorter-wavelength blues. “Soot particles are absorbing blue light from the sun, and we don’t see it,” says Mark Marley, a researcher at NASA’s Ames Research Center who studies the atmosphere of planets outside the solar system from Earth. Huh. Those particles absorbed or scattered the blue color – but let that Mordorish pass through the red-orange.

That smoke was not the only layer in the sky. Beneath it was a sea layer of moist air – San Francisco’s famous Carl Fogg, crawling like steamed milk under the foam of a third-wave latte. Here where some physics creeps as well. Unlike carbon, water vapor is generally more absorbed on the red-orange side of the visible spectrum. But those water molecules, just two hydrogens and one oxygen, are larger than most smoke particles. And in the physics of light scattering, size matters. Down the scale of a molecule or two, a few hundreds of nanometers, light can shift and change the direction around a particle or turn it off and back depending on its wavelength. That is to say, particles of different sizes interact differently with different colors of light.