In March of 1989, the hydroelectric power station in Quebec lost power for several hours, and two thousand satellites temporarily vanished from the tracking system of the United States Air Force.
In September 1859, astronomer Richard Carrington observed a flare of white light on the sun. Seventeen hours and forty minutes later, the effects were seen: fires in telegraph offices, telegraph machines that weren’t set up to send messages suddenly ably to send messages. It became known as the Carrington Event, and its cause was the same as what happened in March of 1989: the sun.
Associated with the release of energy known as a solar flare, the sun sometimes also produces coronal mass ejections (CMEs), large ‘bubbles’ of charged, energetic particles. If the CME hits Earth, its potential effects are notable: extensive auroras, power grid failure, disruption of radio communications, impact on aircraft operations, damage to the onboard electronics of orbiting satellites–including those for communications and GPS. The density of the air around satellites can increase, causing excess drag, and bringing the satellite’s orbit lower, potentially destroying it. These effects are so-called ‘geomagnetic storms’, as they are ‘storms’ caused by the interaction of the charged particles with the Earth’s magnetic field. Geomagnetic storms do not need a CME to occur, but CMEs generally lead to more intensive geomagnetic storms.
As you can imagine, a geomagnetic storm with the intensity of the Carrington event in modern society would be devastating. Loss of power, loss of satellites–the list goes on. Unfortunately, we cannot well predict the sun. Space weather, or the environment in space near Earth, is as unpredictable as the ten-day local weather forecast.
Luckily for us, not all CMEs impact life on Earth. Sometimes, they miss, having been pointed away from our planet. That leads us to today’s paper, “A major solar eruptive event in July 2012: Defining extreme space weather scenarios” by D. N. Baker, X. Li, A. Pulkkinen, C. M. Ngwira, M. L. Mays, A. B. Galvin, and K. D. C. Simunac. The article was published in 2013 in an American Geophysical Union journal called Space Weather. The seven authors of this paper worked together to look at one of the CMEs that missed us. It occurred on the 23rd of July 2012. We’ll return to this in a moment.
The effects of geomagnetic storms are measured using the Dst index. This measures the change in the magnetic field, averaged around the Earth’s equator. The units are nT, or nanoTesla: Tesla is the unit for a magnetic field, and nano is a prefix for 10-9. Dst values of less than -300 nT signal large geomagnetic storms. The Carrington Event was at least -850 nT, possibly up to -1760 nT. The Dst index was not put into place until 1957. Since then, the largest geomagnetic storm was Dst index -589 nT: that was March 1989.
If you are someone working with GPS or communication satellites, space weather and geomagnetic storms are going to be a concern for you. How big can these storms get, and how often do they occur? Right now we don’t have solid answers for those questions, though it has been implied that a Carrington Event type storm is along the same idea as a hundred-year flood: they don’t happen very often, but when they do, they’re quite intense.
This leads us back to the aforementioned July 2012 event. Had it been aimed at the Earth, the authors of today’s paper suspect it would be at least as large as the March 1989 event, but possibly as large–or even larger–than the Carrington Event. A Carrington Event in today’s time could do $2 trillion in damage or more, and take years to fully recover from; we’re quite lucky it missed. The authors of today’s paper suggest the July 2012 event be used as a way to define an extreme event for which we should prepare.
The July 2012 CME was found to travel at a speed of 2500 km/s, give or take 500 km/s 4.5 to 6.7 million miles per hour). In its path was a lone satellite, STEREO-A, which detected the event 19 hours later. STEREO-A and its near twin, STEREO-B, are NASA’s Solar TErrestrial RElations Observatory satellites, which observe the entire sun.
Using the information from STEREO-A and a proven model of finding Dst index values, the July 2012 event was -1182 nT at its most extreme, and near -500 nT with other conditions. Notably, the July 2012 event came at one of the active maxima of the sun’s natural cycle, but it was less active than other maxima. Clearly, the sun can still produce very powerful events even when it is somewhat quiet.
We cannot stop the sun and we cannot yet predict all of its actions. The more we learn the more we can prepare: once again, science works not just for satisfying curiosity, but for the good of society. We are doing what we can to protect ourselves from the more harmful effects of the sun, and research is a part of that. Hopefully, when the next Carrington Event strikes Earth, we’ll be ready for it.
Astronomy Picture of the Day. “APOD: 2013 April 13 – Sun with Solar Flare.” N.p., 13 Apr. 2013. Web. 15 May 2015.
The image of the sun with a solar flare at the start of the post.
Baker, D. N., et al. “A major solar eruptive event in July 2012: Defining extreme space weather scenarios.” Space Weather 11.10 (2013): 585-591.
The main paper for today.
Bennett, Jeffrey et al. The Cosmic Perspective: The Solar System. 7th ed. San Francisco: Addison-Wesley. Print.
A textbook I used for a reference on CMEs.
Fox, Karen C. “STEREO Mission Celebrates Five Incredible Years of Science.” N.p., n.d. Web. 15 May 2015.
An article about STEREO reaching five years, from which I took the artist’s conception of the spacecraft.
National Aeronautics and Space Administration. “July 23, 2012 Super CME Seen by STEREO.” N.p., n.d. Web. 15 May 2015.
The short post where I got the image of the July 2012 CME. Also included figures about the damages of a modern-day Carrington Event.
National Aeronautics and Space Administration “Solar Storm and Space Weather – Frequently Asked Questions.” N.p., n.d. Web. 15 May 2015.
An FAQ pace about solar storms and space weather, used for reference.
National Aeronautics and Space Administration “STEREO.” N.p., n.d. Web. 15 May 2015.
The homepage for the STEREO mission.