Ten years ago, the sun provided an unexpected extra dimension to the tricks and treats of Halloween. The trick was a solar-terrestrial nightmare coming to life. The treat was a spectacular aurora “with green phantom ‘northern lights’ seen as far south as Texas and Florida“.
The solar storm or coronal mass ejection (CME) responsible for this event occurred well after the peak of Solar Cycle 23 in April 2000. It followed months of quiet solar activity characteristic of the waning phase of an average solar cycle. The quiet period ended abruptly and without warning in mid-October with series of solar storms that extended through much of November.
The storm ranks as one of the largest outbreaks of solar activity in recent history (reference: http://www.swpc.noaa.gov/Services/SWstorms_assessment.pdf ). As such it may serve as portent – and heads-up – of what we might expect following the current near peak of Solar Cycle 24 (see more below).
The leading edge of the Halloween CME impacted the Earth’s magnetic field on October 29. It produced a G5 (“extreme”) geomagnetic storm which lasted for twenty seven hours.
This CME had the potential to threaten life as we know it. Such a worst case scenario (as discussed here) would have required the CME to strike with its magnetic field directly opposed to the Earth’s (like the north pole and south pole of a bar magnet). Fortunately, that was not the case. By pure chance, the alignment of the fields were off by just 20 degrees as indicated by sudden changes in simple compass measurements in Alaska. Consequently, geomagnetically induced electrical currents and associated effects were not as large as they might have been.
Nevertheless, the impacts of the Halloween solar storm were wide-ranging and significant. For example: directional drilling for oil and gas in Alaska was disrupted, as well as geophysical surveys around the world; in Northern Europe, geomagnetically induced currents (GIC) caused electrical transformer problems and even a system failure in Sweden which led to widespread blackouts; the storm is believed to be responsible for the complete loss of the $640 million ADEOS 2 spacecraft, along with its $150 million NASA Seawinds instrument; it triggered GPS disruptions to the FAA’s navigation system affecting commercial aircraft precision approaches and keeping the vertical separation of aircraft no less than specified minimums.
Today’s solar storm risks
The Halloween solar storm serves as warning that the threat from the present Solar Cycle 24 remains, notwithstanding an apparent public perception to the contrary.
In fact, it’s not certain that the current solar cycle has peaked yet. Following a very active 2011, solar activity slumped and has remained unusually calm through most of this year. However, Dean Pesnell of NASA’s Global Space Flight Center in Greenbelt argues that the 2011 surge might just have been part one of Solar Cycle 24’s peaks. According to Pesnell (and other space scientists), the last two solar maxima, around 1989 and 2001, had not one but two peaks. Solar activity went up, dipped, then resumed, performing a mini-cycle that lasted about two years, indicating the second peak might occur in mid-to-late 2013 or later, possibly lasting into 2014.
If there is no second peak, the solar maximum actually occurred two years ago. As if on command, however, the sun has become increasingly active with huge solar flares in the just in the past few days. So far, none has been aimed directly Earth, with effects that would have depended upon the CME intensity and orientation of magnetic fields.
The Earth is but a small target in the vastness of space outwards from the Sun, but the distinct possibly of being hit cannot be dismissed. Moreover, some of the most intense solar geomagnetic storms occur not during the solar maximum but years beyond between the maximum and minimum. In fact, the strongest geomagnetic storm on record, the Carrington event of 1859, occurred just before a solar minimum.
Are we prepared for a potentially disastrous solar storm? From all I’ve seen, the answer is the same: “an unequivocal, if not surprising, no” – as I pronounced in July 2012.