A geomagnetic storm lies behind every inspiring aurora in our skies. The mystery behind these shimmering curtains of neon-like light isn’t a mystery to scientists who study space weather. Rather than the calm before the storm, aurora is the light show after the storm in space.
Auroras above the Northern and Southern Hemispheres evolve from the sun’s activity that affects the conditions in space on an enormous scale. Space weather—caused by solar activity such as solar flares and coronal mass ejections—can impact the space between here and the sun and cause an aurora as a byproduct. Auroras can also be triggered by much less energetic events, such as fast solar wind streams from coronal holes. NOAA scientists monitor and track these geomagnetic storms and other phenomena related to space weather.
Space Weather and Magnetism
Although auroral lights appear most frequently in the night sky near the poles—the aurora borealis to the north and the aurora australis to the south—space weather happens on a much larger scale. Solar matter can be flung from our sun’s atmosphere through the space between the planets and can reach the remotest edges of our solar system. These eruptions carry as much energy as a modern nuclear reactor could produce if it ran continuously for hundreds of thousands of years.
When these powerful surges arrive at Earth, they reshape our magnetosphere (pronounced mag-NEAT-ah-sphere). The magnetosphere is the region of space surrounding Earth where the dominant magnetic field is the magnetic field of Earth, rather than the magnetic field of interplanetary space. Electrically conductive plasmas in the solar wind and the magnetosphere are not free to cross into one another, so when solar winds hit the magnetosphere they don’t flow through our magnetic bubble, but must go around. The force of the wind as it impacts and flows around the magnetosphere affects the shape of the magnetosphere. The shape and size of Earth’s magnetic field continually change as the field is buffeted by solar wind, but in general it looks like a giant raindrop surrounding our Earth with the rounded part towards the sun and the long tail away from it.
Earth’s magnetic field lines converge at the geomagnetic north and south poles (which are offset from the geographic poles). Magnetospheric electrons can be accelerated by various processes and hit the atmosphere as they flow along magnetic field lines in the polar regions towards the Earth. There, they collide with oxygen and nitrogen atoms in Earth’s upper atmosphere and emit light in the form of aurora.
Viewing an Aurora Light Show
The chances of glimpsing these spectacular “dancing” lights improve during certain times of the year and under certain space weather conditions. As the sun approaches its solar maximum, the time of greatest solar activity during the roughly 11-year solar activity cycle, auroras often occur more frequently in conjunction with more intense geomagnetic storms. In addition, the closer a skywatcher is to the higher latitudes, the more likely auroras will be visible. However, there’s a catch. Earth's magnetic poles are offset from the geographic poles. Aurora typically occur along a 10° to 20° ring roughly centered on the magnetic poles. NCEI’s World Magnetic Model can be used to calculate the location of the magnetic poles. Many locations in Alaska, for instance, are front-row seats for these amazing light displays.
In North America, auroras are most commonly visible in March and November when cloud cover diminishes somewhat and the nights are longer than the days. Cloudy or overcast skies decrease visibility, but scientists don’t fully understand the reason that auroras are more frequently observed during these months. Auroral lights are usually only viewable near local midnight. They are generally not visible during daylight hours, although on clearer nights, auroras have been viewed within an hour before and after sunrise.
In vivid reds, greens, yellows, and blues, auroras look like wavy or shimmering curtains or have a diffuse glow.. Whatever color or shape, the lights pose a curiosity for tourists and polar residents alike.
The Beauty and Mystery of Aurora
Aurora often appears in highly structured ribbons—sheets as thin as a few hundred meters that can stretch for hundreds of kilometers into the atmosphere. These sheets ripple and move across the sky as the aurora evolves, driven by changes in the shape of Earth’s magnetic field in the “tail” of the magnetosphere hundreds of thousands of kilometers away. The magnetic field in the tail connects back to Earth through the magnetic poles, and the thin sheets we see on Earth can be traced back through space to where the “magnetotail” is energized and stretched by interaction with solar wind and the interplanetary magnetic field.
Perhaps more impressively, each magnetic field line that becomes active at the north magnetic pole has a companion in the south, so as observers in Alaska watch the auroral ribbons dance and move in the sky, observers in the Antarctic could watch their own auroral show. For each twist and wave of the auroral ribbon in the north, its southern companion will do the same, not quite in mirror image, but clearly in coordinated motions. Two observers, separated by thousands of kilometers on Earth—oceans and continents apart—can watch nearly the same auroral show, connected by a link through deep space, more than a hundred thousand kilometers long.
Forecasting Aurora
NOAA keeps tabs on the dynamics of the sun, including watching for explosive solar events and clocking solar wind speeds, to prepare for changes in the magnetosphere, which can cause disruptions in communications and electrical systems on the planet.
At polar regions, the aurora borealis and aurora australis show up about half the nights in a given year. NOAA’s Space Weather Prediction Center develops 30-minute forecasts of aurora over both hemispheres based on solar wind speeds. A 3-day forecast is also available. If you are a citizen scientist, you can report your auroral sightings at Aurorasaurus.
NOAA and NCEI are dedicated to advancing our understanding of the Earth's atmosphere and its interactions with the solar environment. NCEI archives and provides access to solar and space environmental data and derived products that give scientists the means to make forecasts and issue space weather advisories and alerts.
