A Surprise Aurora
By Francis Tarasiewicz
After 17 months of working at New England’s highest peak, it finally happened. On the night of November 12th, 2023, I was lucky enough to view the famous and ever-elusive Aurora Borealis, or northern lights. This blog will chronicle my experience of the night, including the dazzling details of pillars, excited oxygen molecules, and curtains of plasma. Before I can share the exciting details of the night, I feel it necessary to talk a bit about the science behind this awe-inspiring phenomenon, starting from the sun and ending around 60 miles above our heads in our planet’s ionosphere.
The origin of an Aurora can be traced back around 93 million miles away to our closest star, an unassuming yellow dwarf known as the Sun. The Sun is a tiny but mighty energetic body, producing about one trillion watts of energy each second (about 2-3 trillion after you’ve finished reading this brief aside). According to the University Corporation for Atmospheric Research, this is more energy than humans will use in 600 years. A tiny fraction of the Sun’s energy makes it to the top of Earth’s atmosphere, roughly equaling 342 watts of energy per square meter of Earth. Of course, not every part of the Earth receives this energy equally, and so begins the engine of the complex weather and climate machine! My blog, for once, isn’t focused on Earth’s weather; instead, I am tracking billions of tons of material from the Sun that is launched at the upper limits of Earth’s atmosphere, the Ionosphere.
The ejection of material from the Sun is a routine occurrence, and I can assure you that it has a more scientific name than what some of us at the Observatory have termed as “Solar Burps.” Space weather refers to abrupt ejections of mass from the Sun as Coronal Mass Ejections. A CME is a violent burst of plasma (superheated gas) from the Sun into space. CMEs result from localized areas of disturbed magnetic fields (Sun Spots) in the Sun’s Corona or upper atmosphere. A typical CME will send out billions of tons of protons and electrons at speeds of 12 to 2,000 miles per second. These highly energetic bursts may be many times larger than the entire size of Earth as they spread outward into the solar system. The vast majority of these events miss the Earth entirely, as the Earth is tiny compared to the massive size of the Sun. A few, however, do indeed face toward the Earth and interact with its magnetosphere, resulting in the Aurora.
The Earth’s magnetosphere is simply the extent of our planet’s magnetic field. This layer extends about 12 million miles from the surface of the Earth, a distance that is 15 times wider than the Sun! The magnetosphere is vital in that it protects the surface from the constant bombardment of high-energy particles from the Sun and the surrounding cosmos. Without it, the relentless solar wind would make quick work of our fragile atmosphere and eventually all life on the planet. On that rather somber note, let’s take a look at how CMEs interact with this critical layer to create Auroras!
After roughly 40 hours and 93 million miles, an Earth-facing CME makes it to the Earth’s magnetosphere. What happens next heavily depends on the orientation of the solar wind’s magnetic orientation in the up/down direction (Bz). For the best view of an aurora, the Bz direction needs to be negative (south-facing). This indicates that particles are being pushed into Earth’s magnetic field and are producing aurora. This doesn’t mean that aurora can’t happen with a positive Bz; in these cases, the solar storm needs to be much stronger to achieve aurora.
The colors of the aurora come from the interaction of high-energy particles with atoms and molecules in the upper parts of the atmosphere, collectively called the Ionosphere. The ionosphere is a layer of electrified particles in the atmosphere extending from the mesosphere to the thermosphere or 50 to 400 miles above the surface.
At lower levels of the atmosphere, oxygen and nitrogen are much more commonly found in their molecular form (O2 and N2). This simply means that nitrogen and oxygen atoms are more likely to be found in bonded pairs. Further up in the atmosphere, there is much more in the way of elemental or solo oxygen and nitrogen atoms. In the vast stretch of the ionosphere, these elements exist almost entirely as lone atoms, drifting around in a lonely solo dance on the edge of space. The lonely dances of these atoms are suddenly interrupted as energetic streams of wayward protons and electrons from the sun impact the atoms and transfer vast amounts of energy. The now ionized atoms of nitrogen, oxygen, and other trace gases quickly release this energy in the form of light. Oxygen gives off the common green and yellow colors, while nitrogen expresses this release of energy in blue and red hues. Neon can create dazzling orange accents.
Of course, auroras are not only known for their colors; they also lay down some pretty cool dance moves in the upper atmosphere. The wavy curtain patterns form from charged particles traveling along the direction of the magnetic field. The curls and waves result from the acceleration and deceleration of ionized atoms.
On the night of November 11th, a sizable CME impacted the Earth’s magnetosphere. Typically, this would be a non-event for us on the summit, but on this particular night, conditions were prime for viewing the northern lights. A crescent moon set the stage for a darker than normal night sky, dry air from high pressure kept fog at bay, and an undercast of thick low-lying stratus clouds helped to block out lights from surrounding cities. Everything was in place except for…the aurora. The night ended without a whiff of ionized oxygen curtains and disappointment.
On the summit, we resigned to accept another disappointing event and went about our daily changing of the shift. After a long shift, I logged onto my phone and began my nightly mindless scrolling on my phone. To my shock, my normally weather-centric social media feeds were filled with reports of aurora across the upper Midwest and Maine. It was happening! A quick glimpse of the New England Outdoor Center camera from Baxter State Park revealed stunning pillars of purple and green stretching across the northern sky. After seeing this, I raced up the tower and into the 14 degree night. Outside, I found fellow weather observer Ryan Knapp doing what he does best, documenting the northern light with his trusty camera. It’s always a cool experience to see a master at work on their craft, and nighttime aurora photography by Ryan is no exception.
After a few minutes of intently staring at the sky beyond the Northern Presidential range, an eerie blue-green glow began to emerge. I was definitely thankful to have someone with over a decade of aurora viewing experience pointing out the faint fuzz on the northern horizon. Had I been by myself, I would have easily mistaken the glow for city lights from Montreal. The lights maintained their faint glow for a freezing 30 minutes and then suddenly began to morph into something more spectacular. Odd pillars of light began to emerge from the glimmer, and soon the glimmer organized into a structured layer of ribbons. The ribbons were a faint green color at their base with a reddish-purple hue accenting the very tops of them. Pillars danced across the sky and seemed to move impossibly fast in the darkness. I watched these columns expand from a faint arc to the north, to the northeast, and eventually the entire northern sky.
We called out specific peaks to indicate where one of us spotted a developing spire or a quick movement of the curtain. “There’s a pillar over (Mt.) Madison!” proclaimed Ryan. My responses of course were limited to simple “wows” or “that’s pretty sweet”. Throughout this time, I watched the constellation Orion as it emerged from the southern horizon. In the time it took for the curtains to fade back into a faint green glow, I noticed that Orion had moved from just barely poking above the horizon to taking its place of prominence as the hunter in the southern sky.
Aurora with pillars.
My biggest piece of advice following this celestial display is that when the aurora is forecast to dance in your skies please modify your expectations. Many of us expect all aurora events to feature sheets of red-green trails all across the sky. The reality is that for most of us who dwell in the mid-latitudes, these types of events rarely occur, if ever. That’s not to say that this is something that you’ll want to miss out on. Just be sure to bring along a camera with decent long exposure capabilities and allow your eyes to adjust to the night sky.