In general, when an Aurora borealis flashes across the night sky - anywhere- curious humans will be attracted to the display and even seek it out. Such as an Aurora we beheld in Chena Hot Springs, AK in March, 2005, e.g.
However, when a rare aurora occurred over northern Colorado at the end of March, space scientists in Boulder were less fascinated by the appearance than the potential physical effects. They were instead well aware that a geomagnetic storm had emanated from the Sun two days earlier (see lower graphic) and also that a coronal mass ejection (CME) was due to arrive.
Their concern over any impeding impact over the appearance was well justified. They knew that the "ultimate" CME is that which smacks us broadside, knocking down power grids like tenpins, and disrupting other critical services, (weather and defense satellite monitoring, GPS) dependent on spacecraft. CMEs can also disrupt aircraft communication and navigation systems, interfere with radio transmissions and disseminate enormous voltage surges such as knocked out the Ottawa power grid in 1989, e.g.
Hence, it is of interest to attempt to forecast these violent plasma outbursts. The job of Boulder's Space Weather Prediction Center (SWPC) is to alert those potentially impacted industries so they can take precautions. Forecasting geomagnetic events is the primary mission of SWPC but its interest wasn’t primarily in alerting skygazers to the rare pink and purple displays some Coloradans saw on March 30. The much higher priority in that office- a division of the NOAA - involves warning industries that can be damaged by solar eruptions called coronal mass ejections (CMEs). In the words of Bill Murtagh, a space scientist at SWPC, in an interview at the time with The Denver Post:
“We’re not that interested in the aurora as a sight. We’re interested in the effects on technology.”
In the case of the late March event, scientists detected an active sunspot group that became especially active on March 28, producing two solar flares and CMEs. En route to Earth, they merged into one. When that happens, it’s called a cannibal CME. As space scientist Murtagh explained:
“We had to figure out, are these coronal mass ejections Earth-bound? They can be shooting off to the left or the right or the other side of the Sun. Or, when the eruption is just at the right location, they’re heading toward Earth. In this situation, we were quick to realize that they were heading directly toward Earth. We plugged the measurements we made of the eruption into our model and it gave us a sense of if, and when, that thing was going to hit Earth. It was clear that it was going to impact the Earth late on the 30th and into the 31st.”
After a CME is
detected, the Boulder scientists turn to a satellite a million miles from
Earth, which they use to measure the CME’s brightness, size and speed. Murtagh again:
“We’ll take that information, stick it in a model, and the models say, ‘Based on that, this CME is going to get here in 48 hours.’ When the CME hits our spacecraft, now we know it’s about to hit Earth, it’s about 30 minutes away,”
Adding:
“We
can dissect the CME to see what the magnetic structure is, and the temperature.
Then we have a good solid understanding of how the Earth’s magnetic field is
going to respond to that thing we predicted two days out.”
CME’s can travel
at speeds from 1 million to 6 million miles per hour, and the N. Colorado- associated event traveled at about 2 million mph. The SWPC alerted power grid
operators and managers of other vulnerable systems so they could prepare for a
surge of electricity. In Murtagh's words:
“With the power
grid, there are two (concerns). One is the vulnerability of our
extra high (voltage) transformers. The power grid is an AC (alternating
current) network. We induce a DC (direct) current into that system and those
transformers do not like that. That can cause heating and damage to the
windings of the transformers. It’s one of our big fears. If we get an extreme
event, it can damage dozens or even hundreds of those transformers. The
consequences to the nation could be significant.”
Another concern for space forecasts is the voltage irregularity resulting from the geomagnetic impulse that could
trip up electrical systems. In Murtagh's assessement that would be more like "tripping a fuse" - perhaps causing a widespread blackout but with the recovery time much shorter than from a full on impact. The damage extending over hours to a couple days and measured in billions of dollars as opposed to trillions.
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