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July-August 2017

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Photographing Weather in the Dark

What is the most essential tool for a die-hard weather enthusiast? A thermometer? Or maybe a barometer? I would maintain it is a camera. The theater of the sky is an ever-changing pageant of performance art starring water, dust, air, and light. While a geologist can always check out that rock next year, you will never see the same sky twice. Capture that amazing skyscape now—or it is gone. Forever. The over 40,000 members of the Cloud Appreciation Society get that. Ever see a storm chaser without a camera? And with the amazing advances in affordable camera technology, today everybody is a photographer and/or videographer. (Did you know that handy Instagram/YouTube/Facebook/etc. capture device in your pocket also makes phone calls?)

Whatever tool you use, from smart phone to a point-and-shoot or a modern digital single-lens reflex (DSLR) or mirrorless camera, or even high-end professional rigs, when the sun goes down, most weather geeks head inside, maybe to check the model runs for tomorrow's chase. It is dark outside. Nothing to see there. Oh sure, the astrophotographers emerge at night for the sprawling Milky Way, an impressive planetary conjunction, or a Perseid meteor shooting overhead, but they only come out when the weather is clear. Shutter clicks on a cloudy night are few and far between. For most weather and photo lovers, when it's dark, we slumber. And boy, have we been missing some amazing shots.

Painting with Light

The word photography is derived from the Greek, meaning “painting with light.” Light is the essential ingredient. It is no wonder that the hours after sunset are considered down time. Attempts to capture images of the real world date back at least to the Middle Ages when the pinhole camera (camera obscura in Latin) projected the outside view, albeit inverted, into a darkened room. Painters used this technique to create “photorealistic” scenes. It was not until about 1800 that Englishman Thomas Wedgwood (scion of the famous china making family) used silver nitrate impregnated materials to copy the projected light. Yet he was unable to “fix” the image, so unless kept in the dark, it soon faded away. By 1826, Frenchman Nicephore Niepce appears to have made the first permanent photograph, showing a rooftop—and the sky. By 1839, Louis Daguerre debuted his more practical Daguerreotype, the earliest known example showing a Paris street (and sky). The exposure time must have been several minutes, however, as the crowded scene showed no people, except for one man standing still while getting his shoes shined. The fast street traffic was blurred out of the image. Exposure time is one of the three primary factors in painting with light. Many cameras typically can elect shutter speeds from 1/8,000 second to 30 seconds (or more). The longer the shutter stays open, the more light is captured. The second factor is how wide the shutter is opened, called the aperture. This is measured in f-stops. We don't have time for a complete photography lesson here, but the wider a lens can open (to f/2.0 or f/2.8), the more light gets in. The more the lens is “stopped down,” to say f/22, the less light is grabbed. But the final determinant is the light sensitivity of the capture medium. In the days of silver salts on paper, it took minutes. More practical photographic films came in a variety of sensitivities. Back in the day, film speed was rated by ASA units (American Standards Association). Color Kodachrome film (of Paul Simon song fame) had an ASA of 25. It was slow—not very sensitive. You needed a long exposure and/or a wide lens aperture. Tri-X film, ASA 400, was the racehorse of the film world. But as ASA went up, so did the graininess and lack of sharpness. Even shooting in the shade was tricky. Legendary photographer Ansel Adams's most famous picture, “Moonrise Hernandez New Mexico 1941,” appears to show a full moon in a dark night sky over a gorgeous display of altocumulus lenticular mountain wave clouds. Yet, truth be told, it was an exposure at ASA 64 stopped way down to f/32 while using a filter to blacken to sky. The time was 4:05 p.m. The sun was still up.

Skip forward to 1975. An electrical engineer named Steven Sasson developed the world's first digital camera. The lenses were still there, but the film was replaced by a charged coupled device (CCD) that had minute pixels that grabbed and counted the incoming light photons. That first camera had 0.01 megapixels (MP)—a very coarse image indeed. The camera on my desk has 42 MP, or 4,200 times more resolution, creating a very detailed image. But beyond their high resolution, the cameras of today are vastly more sensitive. Along the way ASA became ISO (pronounced “eye-sew”) after the International Organization for Standardization. One camera I would like to own has a peak ISO of 3,280,000. The one on my desk “only” gets to 409,600 ISO. Given that the amount of light captured (all else being equal) doubles every time the ISO doubles, my little mirrorless camera captures 10 times more light than Adams's massive 8 × 10 inch view camera. Could Ansel Adams, using today's tools, reshoot his iconic desert image by moonlight at night? I'm pretty sure he could. Even a quarter moon can often do the job.

Of course, pictures are easier if a night scene contains something really, really bright, such as William Jennings first lightning capture in the 1880s. He didn't need a flash bulb! Night lightning photography is fun. One can either leave the shutter open for many seconds until the flash, or use a lightning trigger to catch the brilliant return stroke, though not much else. With today's high ISO cameras, both the nighttime bolt and the parent storm cloudscape can be frozen in time for all to admire.

When Is It Night?

According to the classic Ray Charles song, “The Night Time Is the Right Time.” For weather photography, we could not agree more. Though when, exactly, is nighttime? Sunset (or sunrise) is defined as the moment when the center of the sun's disk is 0.83 degrees below the horizon. After the sun's disk disappears, we then experience civil twilight, then nautical twilight, and finally astronomical twilight. The sky is not fully dark until the sun is 18 degrees below the horizon. In that hour or more of failing skylight, many interesting shots await, including high clouds still illuminated by the sun, silhouetted terrain and clouds, crepuscular rays (in the west), and anticrepuscular rays in the eastern sky, along with the pink and purple hues of the Belt of Venus marking the terminator zone separating sunlight and the earth's shadow. And if you are very fortunate, the luminous ripples of upper atmosphere noctilucent clouds might just appear.

When it finally gets really, really dark, what is the drill? People with point-and-shoot pocket cameras on the edge of the Grand Canyon using their flash at night are guaranteed disappointment. However, if stars and silhouettes are your thing, be brave, switch your camera from auto to manual mode, and experiment. There is no film to “waste” with a digital camera, so clicks cost you nothing. Open up the lens aperture, crank up the ISO, and/or lengthen the exposure. Start with f/4, maybe 3200 or 6400 ISO, for several or more seconds. You don't need an expensive camera, but you do need a tripod. Remotely triggering the camera with one of many smart phone apps or low-cost manual releases (which can also take time lapse sequences) is recommended as well. Unlike our astronomy friends, you might soon be cheering when interesting cloud forms enter the field of view. Want to get “artsy?” Try light painting foreground trees and rocks. Sweep a high power “tactical” flashlight beam across the subjects for several seconds of what might be a 20 second exposure.

When it is clouds you want to shoot, unless you have a searchlight from a Hollywood movie premier, light painting isn't up to the task. Happily, a little moonlight can go a long way. Moonbeams shining from behind a building thunderhead provide just one of a million options. A full moon might be a good time to catch a moonbow in the blowing mist from a waterfall, not to mention lunar halos and coronas. While light pollution is the bane of astrophotographers, make it work for you. Upwelling city lights illuminate cloud bases with some startling effects. Or head to the hills on a night when valley fog is predicted. City lights creating spooky apparitions in the fog swirls below can be enchanting. Calm, bitter-cold winter nights can bring a rare treat, as ghostly spires of light pillars tower above terrestrial lights reflecting off a myriad of floating ice crystals. Really long exposures create special effects, such as star trails and time-blurred cloudscapes. And do experiment. If the shot is a dud, delete it from your card. Then try, try again.

What Is Light?

So what is light? If you ask your neighborhood physicist, he/she will wax poetic about it being both a particle and a wave. Well, let's look at the wave part. The human eye evolved to see a relatively narrow portion of the electromagnetic spectrum, wavelengths between 400 and 700 nanometers. (One nanometer is one billionth of a meter. That's very small.) Somewhat shorter wavelengths (less than 400 nanometers) contain the ultraviolet. Longer wavelengths include the near infrared (NIR) just above 700 nanometers, while the thermal infrared is around 12,000 nanometers (or 12 micrometers). Your camera is designed to record only from 400–700 nanometers. And what if there really is no visible light at all? Satellite meteorologists solved that one decades ago. In 1960, the first Television Infrared Observation Satellite (TIROS 1) used a TV camera by day and a heat camera by night. A winter energy audit of your home uses a thermal infrared scan to pinpoint hot spots leaking energy. Night satellite pictures work the same way, by converting the warmth or coolness of the cloud tops into maps we can understand—no visible light needed. Infrared imagery, however, can't distinguish everything. So early military satellites employed sensors that could see at night with only a modest amount of moonlight. City lights are almost blinding to these sensors, enabling the familiar “earth at night” maps outlining human habitation across the globe. This technology gradually migrated into today's cameras. But the satellites keep improving. The Suomi NPP, launched in late 2011, is the prototype for the next generation of polar orbiting weather satellites. It scans the earth using 22 wavelength bands from visible to infrared. One of these is quite special, the Day Night Band (DNB), which images in the visible and NIR. It is so sensitive that even a hint of moonlight is all it needs to map clouds.

Then came the surprise. The engineers did such a good job that all manner of strange structures were appearing—on totally moonless nights. It turns out the atmosphere glows. A truly black sky (even if the stars could be turned off) is hard to find. Solar energy is captured by certain atoms in the upper atmosphere (53–59 miles up), which is then released at night in the red and green colors of airglow (aka nightglow). Plus it takes only a tiny disturbance to make the airglow get dimmer and brighter. One such disruptor are the gravity waves that are constantly propagating upward from sources as diverse as earthquakes, volcanoes, frontal systems, jet streams, flow over mountains, and thunderstorms. The DNB was capturing glowing circular ripples of light above intense storms, telling scientists a lot about the workings of the middle atmosphere—a place that is notoriously difficult to make measurements.

Citizen Scientists Working the Night Shift

So why go through all of steps outlined above? In 1989, the first of the TLEs—the lightning-induced red sprite—was discovered on video, glowing between 25 and 55 miles above a thunderstorm. TLEs? Transient (they last far less than a second) luminous (though very, very dim) events (because if you see one, it is quite an event). Initially sprite photographs required an expensive space-shuttle class camera designed for extreme low-light video. By around 2005, technology had improved so much that tiny cameras costing only a few hundred dollars took useful black and white TLE videos. Networks of sprite cameras were established, and not just by scientists. Eager weather enthusiasts wanted in on the action. Once described by the vaguely disparaging term “amateurs,” these dedicated people, while perhaps lacking formal training in the field, were highly motivated, self-taught, and sometimes quite well equipped. Today these “citizen scientists” are making meaningful contributions to the field. As camera technology matured, the rush was on to capture TLEs in living color and high resolution, all the while working closely with government and university science teams to arrive at some real breakthroughs.

Thomas Ashcraft, by profession an artist and by avocation a radio enthusiast, meteor and bolide hunter, and sprite chaser extraordinaire, was recently profiled in the New York Times. From his outpost on the New Mexico plains, he tried something new. Sacrificing an older camera, he used a commercial service to remove the “IR cut filter” from in front of the sensor. This allowed not just the visible but NIR light onto the sensor, greatly increasing the sprite resolving capability. And then his photos saw something else. A thunderstorm over Texas was spewing sprites and also convectively generated gravity waves (CGGWs) that lit up the airglow high above the storm. Just then, Suomi NPP flew overhead. The DNB imager mapped the pattern of waves expanding like ripples after dropping a rock in a pond. This provided a crowning example of the value of night sky photography for ground-truthing what the satellite was seeing.

Sprites are amazing, but the gigantic jet is mind blowing. In less than a second, a glowing channel streaks up from the cloud top to make a direct electrical connection with the ionosphere 55 miles above. First captured in 2001, gigantic jets have been as elusive as they are spectacular. But citizen scientists like Texans James Bunnell and Kevin Palivec kept capturing them with black and white cameras, allowing researchers to slowly tease out scientific details. In southwestern Puerto Rico, Frankie Lucena began sprite hunting a few years back, using his everyday camera gear. In 2011, lady luck smiled and he caught one of the first ever color images of a gigantic jet. It clearly showed the bright blue-white stem emerging from the tall thunderstorm, which faded with altitude into a blue flame, and finally tens of miles higher became a red flare. The colors tell a lot about the energetics and physics involved. In 2014, Australian storm chaser Jacci Ingham was stalking supercells with her DSLR one night in the outback near Darwin. The resulting high-resolution, color image of a gigantic jet was breathtaking.

Come October 2016, Frankie Lucena was again scanning the skies in the direction of then Category 5 Hurricane Matthew as it churned off the coast of Venezuela. Lucena recorded an outburst of 21 sprites in 90 minutes, presumably from intense convection in the storm's outer rainbands. Better yet, upon carefully inspecting and animating his images, he saw distinct patterns in the airglow as CGGWs expanded outward above Matthew's core. And did the Suomi NPP pass overhead and map the radiating pattern of airglow waves? Yup. Along with Lucena's time lapse images, much will be learned about the atmospheric waves, which are key to the dynamics of the mesosphere.

The Day Night Band (DNB) imager on the Suomi NPP satellite captured a large semi-circular region of airglow ripples at 55 miles altitude generated by the deep convection within Hurricane Matthew north of Venezuela. A citizen scientist's camera in Puerto Rico documented both the waves and numerous red sprites.

The Day Night Band (DNB) imager on the Suomi NPP satellite captured a large semi-circular region of airglow ripples at 55 miles altitude generated by the deep convection within Hurricane Matthew north of Venezuela. A citizen scientist's camera in Puerto Rico documented both the waves and numerous red sprites. CIRA/COLORADO STATE UNIVERSITY/STEVE MILLER

In 2016, Jacci Ingham decided it was time for some more night storm chasing, as she was pursuing a supercell in the Northern Territories that would have looked at home in Kansas. Being close to the storm, she trained her DLSR camera on the powerful updraft and exploding anvil cloud. Along with the expected lightning flashes within the cloud, intensely blue light patches a few hundred yards across peppered the underside of the storm's anvil every few seconds. These were not regular lightning. Rather they resembled reports of brief, blue dots of light captured by a similar camera on the International Space Station and special scanners on a TLE-hunting satellite (Formosat 2). In sharing her findings with the scientific community, it may be that she captured a visible manifestation of something called “fast positive breakdown,” now thought to be the beginning stages of almost all lightning discharges. Sometimes they never reach full lightning status and die out, but not before giving off powerful bursts of radio energy and deep blue (and ultraviolet?) light. This is cutting edge research, so stay tuned.

Citizen scientists and enthusiasts, armed with equipment no different from what you may have in your camera bag, along with curiosity (and realizing the night is their friend), are making meaningful contributions to atmospheric science. With social media, you can share your shots with the world. And yes, scientists do monitor these sites. Crowd sourcing of “amateur” photos and videos of severe weather events is becoming more widely used by researchers. Web sites like SpaceWeather.com, twanight.org, and CloudAppreciationSociety.org are great venues to find inspiration. And don't forget the Weatherwise Photo Contest! For some more examples of night skyscapes, try https://weathervideohd.tv/wvhd.php?mod=clipbin&share=b06aa946x22c.

So, go out and shoot something! If it is a shot in the dark, who knows, you might just shed some light on an atmospheric phenomenon awaiting to be explored. And at the very least, make the spirit of Ansel Adams very jealous.

 

WALTER LYONS, Certified Consulting Meteorologist, is a past president of the American Meteorological Society. His career path has included establishing lightning detection networks and investigating sprites, elves, halos, and gigantic jets high above thunderstorms. He is president of the educational Web site, www.WeatherVideoHD.TV.

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