There was a “Carrington Event” that caused aurora below +/-30° latitude in 1770. Are these events more common than we first thought?

A paper by H. Hayakawa to Astrophysical Journal Letters (published in 2017) reports on “Long-lasting extreme magnetic storm activities in 1770 found in historical documents”.

A coronal mass ejection (CME)

The paper reports that the events of September 1770 rivalled the geomagnetic conditions that were reported during the infamous Carrington Event of September 1-2 1859:

“Dim red aurora at low magnetic latitudes is a visual and recognized manifestation of geomagnetic storms. The great low-latitude auroral displays seen throughout East Asia on 16-18 September 1770 are considered to manifest one of the greatest storms. Recently found 111 historical documents in East Asia attest that these low-latitude auroral displays were succeeding for almost 9 nights during 10-19 September 1770 in the lowest magnetic latitude areas (< 30°). This suggests that the duration of the great magnetic storm is much longer than usual. Sunspot drawings from 1770 reveals the fact that sunspots area was twice as large as those observed in another great storm of 1859, which substantiates this unusual storm activities in 1770. These spots likely ejected several huge, sequential magnetic structures in short duration into interplanetary space, resulting in spectacular world-wide aurorae in mid-September 1770. These findings provide new insights about the history, duration, and effects of extreme magnetic storms that may be valuable for those who need to mitigate against extreme events. “

Read the full report here (pdf).

Earth narrowly narrowly missed a Carrington-strength geomagnetic storm in July 2012, when a super-sized CME erupted from the sun, but at an angle that crossed Earth’s orbit about 90° ahead of the Earth. Another one narrowly missed us in April 2014, passing behind us in our orbit.

Some sources suggested that, on average, a “Carrington Event” will happen every 150 years. The time between the 1770 and 1859 events was 89 years. From 1859 to 2012 was 153 years. But the same source suggests that over the next three years (from 2017) there was a one-in-eight chance of us being directly hit by one. This figure seems confused, as said that as of 2012 (when the article was written) there was also a one-in-eight chance of a “catastrophic solar mega-storm” before 2020. Well, it’s now well into 2018, with only 20 months to go until 2020…

Our sun is currently close to the solar minimum between two solar cycles, but don’t let that fool you. Major solar eruptions can occur at any time. Should we be preparing with even more urgency? It’s even worse for us during the solar minimum, because our magnetic field has let it’s guard down due to the decreased activity. The magnetic field isn’t as strong as it is at maximum because the solar wind is weaker. A big CME will be able to blast its way though the weakened defences causing even more havoc to satellites in LEO and to infrastructure on the ground. Now, more than ever, we need to be taking action to protect our infrastructure and harden our technology to the coming threat.

The general public tend to ignore anything other than an immediate threat to their daily lives. Solar storms affect relatively few people on a daily basis, yet a Carrington Event hitting Earth squarely (circularly?) between the eyes will affect millions, and potentially billions of us. Perhaps it’s seen as just another one of those global catastrophes that we can do nothing about?

The AMS (American Meteorological Society) is working towards a “Space Weather Certification” for broadcast weather forecasting which should be concluded within a few years. The aim is to provide knowledge and tools to forecasters so that space weather can be introduced into TV, radio and online weather forecasts. In turn, this will help to educate the public about the daily influence of our nearest star, and hopefully make the forecasting of the effects of solar storms become as commonplace as forecasting the effects of an approaching terrestrial storm. In the meantime, we must build our essential technologies with enough safeguards to survive the next Carrington Event.
© 2018 Andy Smith