Besides blooming flowers, spring is also the aurora season, and last weekend a massive geomagnetic storm created a particularly stunning display.
Like Earth, the sun has its seasons, called the solar minimum (a period of less activity) and the solar maximum (heightened activity). They last much longer than earth seasons, 11 years, but they are reliably cyclic. In 2019, our sun entered its solar maximum phase, which will climax five years from now. This year, the most intense storm of the current cycle happened to occur at the equinox itself, Friday night to Saturday morning.
What are the northern lights?
There are two magnetic fields at play — the Earth’s and the Interplanetary Magnetic Field carried by the solar wind. While Earth’s magnetic field stays fixed over long periods (100,000s of years), the IMF fluctuates around the equinoxes, creating openings called cracks. These cracks allow particles from the solar wind to enter the magnetosphere, triggering the auroral displays. The ionization when the solar wind collides with the upper atmosphere creates a variety of colors.
The IMF “can change its orientation within an evening,” explains Lynn Moorman, a professor of Earth and Environmental Sciences at Mount Royal University in Calgary, Canada. “It’s when it’s orienting south that we go running out [to see the lights].”
Why around the equinoxes? That remains unclear, says Moorman. “It’s probably safe to say that it aligns with specific earth-sun geometry and the spatial relationships between the magnetic fields at the time of equinoxes, although the reasons aren’t well defined yet.”
Photo: Canadian Space Agency
Two days before the equinox, space weather forecasters predicted increased solar winds because of a disturbance in the Sun’s southern hemisphere. The storm reached Earth two days later and was seen all over Canada and parts of the northern United States.
Solar activity is graded on a scale of 1 to 5. This storm was Grade 2, which isn’t too bad, except for a few communications glitches. Grade 5 is the worst and happens every two or three years, causing power grids, communications, and navigational services to collapse, and major technical problems on the International Space Station.
We can expect more powerful aurora in September. A Canadian aurora enthusiast and photographer did a time-lapse of the event, below, with a particularly cool foreground.
