Drive nearly 500 kilometers at night on winter roads through Canada’s Rocky Mountains? Not a problem, says Paul Zizka. He will drop anything at anytime and head out the door of his home in Banff, Alberta, to go hunting—and don’t expect him back before 5 A.M. What is his quarry? The aurora borealis, or northern lights: one of the most magnificent natural phenomena imaginable. “If you’ve seen the aurora,” he says, “you know why. It’s something you never forget.”
Zizka is a world-class photographer. He is also an aurora chaser, part of a unique and devoted fraternity who spend hours deciphering graphs of interplanetary magnetic fields and proton fluxes, trying to determine the optimal time and place to witness the type of geomagnetic storm that manifests itself in the breathtaking greens, pinks and reds of an auroral display.
Like storm chasers who pursue tornadoes in the U.S. Midwest, Zizka and other aurora chasers monitor meteorological data to get as close to the action as possible. Getting caught in the middle of the light storm is the aurora chaser’s dream. “I never get tired of seeing it,” Zizka says, “because it shows itself in so many ways, different colors and textures
Auroras appear with greater frequency closer to the poles (in the southern hemisphere, the phenomenon is known as the aurora australis, or southern lights). In Fairbanks, Alaska, they appear most nights Their relative rarity at Zizka’s lower latitude in more southerly Banff, however, means it takes more work, patience and anticipation for a single viewing. From the moment he wakes, he monitors Facebook groups, Twitter and a number of Web sites, including the National Weather Service’s Space Weather Prediction Center—the official source of space weather in the U.S.—which compiles information from both Earth-based instruments and satellites about solar activity. Space weather Web sites update more often than most news sites, some as often as every eight seconds. They track everything from solar flares and coronal mass ejections (CMEs) to the speed and density of the solar wind and their magnetic fields.
Charged particles periodically erupt from the sun’s surface, as a CME, and create solar winds that race toward Earth, at times in excess of 1,000 kilometers a second. Earth’s magnetic field deflects most of these charged particles. Sometimes, however, when the magnetic fields are oriented in opposite directions (Earth’s points north so the interplanetary magnetic field, or IMF, has to point south), the magnetic shield is essentially down and energy from the solar wind penetrates into near-Earth space. This triggers space weather storms that accelerate electrons that rain down into the atmosphere and excite oxygen and nitrogen atoms. The energy released from these interactions creates the aurora’s glowing, shimmering patterns.
Solar wind speeds are typically around 300 kilometers a second but jump higher when a CME arrives. A sudden surge in wind speed and a southward-oriented IMF means that more energy can be coupled to Earth’s magnetosphere. One directional component of the IMF that matters for the aurora is the Bz value, measured in nanotesla units. Negative values indicate a southward oriented field, so the more negative the Bz value (along with a surge in solar wind speeds for a few days), the better the chance of an auroral display. Other variables, such as the solar wind’s proton density and Kp values that gauge the severity of near-Earth geomagnetic activity, come into play—and the higher they are, the more likely the aurora.
Local weather can still thwart a show at the last minute, turning an anticipated auroral dance into a showdown with thick clouds. On those nights, Zizka stays in touch with the local aurora-chasing community. Texts pour in, reporting holes in the clouds from the foothills or neighboring valleys. Zizka recalls one long night at a nearby mountain lake when the solar weather cooperated perfectly but the local weather did not. “It was really cloudy, and you could tell something wild was happening behind the clouds because the sky was that crazy green, but you couldn’t see any definition. But I stuck it out, and eventually at 3 or 4 A.M. the skies opened up, and we got a beautiful display. It is so rewarding to finally see something when you’ve been sitting there for awhile!”
Zizka’s nighttime mountain adventures don’t all culminate in the sighting of the aurora—far from it. Even during the peak of the 11-year solar cycle, when solar activity is at its highest and the aurora are more frequent, at Zizka’s latitude this only translates into successful sightings three to four nights a month, at best. His consolation prize at least on clear nights might be an unparalleled view of the Milky Way, a meteor shower or an encounter with a pack of wolves howling in the moonlight. Zizka says he has a deep appreciation for the entirety of the experience in this arresting landscape. But it’s the aurora that draws him back night after night, bundled up against the cold, setting up his camera on a frozen lake, hoping for another chance to capture an image of the ephemeral, sparkling winter sky that is unlike anything else in the world.