Dimmer, but not done for a decade
QUIETER SOLAR ACTIVITY MEANS NORTHERN LIGHTS WILL SHINE A LITTLE LESS
There is a lot of chatter around the internet these days about the dimming of the northern lights, and its effect on everything from tourism and telecommunications to space flight and climate change. Airbnb is even touting several northern and Arctic locations as “last-chance” opportunities to see the northern lights in all their glory before they “dim for a decade.” Sortland, for example, a town in the northern Arctic reaches of Norway, has reportedly seen a nearly 1,000-per-cent increase in short-term rental bookings. Airbnb also says Whitehorse, Yukon, is a top prospect for aurora viewing in the coming solar minimum, perhaps more credibly than the far more southerly and temperate Haliburton Highlands of Ontario. This fading of the northern lights is a common and perennial worry, so much so that earlier this year Fox News simply republished a three-year-old article about the “last chance to see the northern lights.” There is something to the concern, even if it has been hyped and the northern lights are almost certain to keep shining as long as the sun keeps burning. The sun is a giant ball of gas that rotates on approximately a monthly cycle, faster at the equator than the poles. The effect of this is a dynamo that makes a magnetic field, which is not uniform, and throws up magnetic explosion as sunspots — dark spots visible on the surface. Over the last century, scientists have discerned regular patterns in the size and frequency of sunspots, and come to see them as a measure of solar activity. The main pattern is a 22-year cycle in which solar activity peaks every 11 years, while also reversing the polarity. After last peaking in 2014, this solar cycle is entering its low phase next year, which is anticipated to be especially low. That is because longer-term trends show that the most recent cycle had a maximum that was overdue and smaller than previous cycles. The last minimum, in 2009, was especially quiet, with no sunspots on 260 out of 365 days. The next solar minimum is expected next year. The magnetic activity also causes the sun to emit intensely hot charged particles from its upper atmosphere, known as the corona, or crown. As they travel toward Earth, these particles follow a path set by the planet’s own magnetic field. This sends them curving toward the poles. Eventually they reach Earth’s atmosphere, where they collide with particles, and the collision is visible as light. The effect is named for the Latin word for “dawn” — Aurora borealis in the north, Aurora australis in the south — and the story is that they were once thought to be the first wisps of daylight. The colour depends on what atom is hit. Nitrogen glows blue or violet, oxygen more green. Red is from higher altitude oxygen. So the worries are partly justified. Reduced solar activity during the solar minimum is likely to show itself in less intense and less frequent northern lights. Another effect of the minimum is to increase risk from space junk to satellites in low Earth orbit. Normally, the radiation from the sun heats up the atmosphere and causes it to expand. As satellites and space junk pass through this, they are slowed by the drag. Eventually, this will cause them to fall towards Earth, and so the process is like an orbital vacuum cleaner. In solar minimum, however, the radiation is decreased, and the atmosphere contracts a bit, leaving less matter to cause drag on things in orbit. As a NASA report put it, “space junk tends to hang around.” There are also associations to climate, the best known being the Maunder Minimum, a period in the late 17th century that coincided with a well-documented cold period in Renaissance Europe. This has led to dire predictions of a coming Ice Age. The best recent science on the climatic effects, however, only really applies to the highest levels of Earth’s atmosphere, not the lower regions that are most affected by human industry and pollution. There is a satellite experiment run by NASA, for example, that has observed a cooling trend in this upper atmosphere that appears to be approaching a record low.