29 January 2020

Likelihood of space super-storms estimated from longest period of magnetic field observations

Posted by larryohanlon

A ‘great’ space weather super-storm, large enough to cause significant disruption to our electronic and networked systems, occurred on average once in every 25 years according to a new study in the AGU journal Geophysical Research Letters.

By analyzing magnetic field records at opposite ends of the Earth (UK and Australia) scientists at the University of Warwick and the British Antarctic Survey have been able to detect super-storms going back over the last 150 years. This result was made possible by a new way of analyzing historical data from the last 14 solar cycles, stretching back to before the space age began in 1957, instead of being limited to the last five solar cycles, which are currently used.

The analysis shows that ‘severe’ magnetic storms occurred in 42 out of the last 150 years, and ‘great’ super-storms occurred in 6 years out of 150. Typically, a storm may only last a few days but can be hugely disruptive to modern technology. Super-storms can cause power blackouts, take out satellites, disrupt aviation and cause temporary loss of GPS signals and radio communications.

“These super-storms are rare events but estimating their chance of occurrence is an important part of planning the level of mitigation needed to protect critical national infrastructure.” said lead author Sandra Chapman of the University of Warwick’s Centre for Fusion, Space and Astrophysics. “This research proposes a new method to approach historical data, to provide a better picture of the chance of occurrence of super-storms and what super-storm activity we are likely to see in the future.”

The Carrington storm of 1859 is widely recognized as the largest super-storm on record, but predates even the data used in this study. The new analysis estimates what amplitude the Carrington Event would need to have been to be in the same class as the other super-storms. From that information, a chance of future Carrington-like events can be estimated.

Sunspots of September 1, 1859, as sketched by English astronomer Richard Carrington. These spots were the source of the space weather that caused the historic geomagnetic super storm known as the Carrington Event of 1859. 

“Our research shows that a super-storm can happen more often than we thought,” said Richard Horne, a space weather researcher at the British Antarctic Survey. “Don’t be misled by the stats. It can happen any time. We simply don’t know when, and right now we can’t predict when.”

Space weather is driven by activity from the sun. Smaller scale storms are common, but occasionally larger storms occur that can have a significant impact.

One way to monitor this space weather is by observing changes in the magnetic field at the earth’s surface. High-quality observations at multiple stations have been available since 1957. The sun has an approximately 11-year cycle of activity which varies in intensity and this data covers five cycles of solar activity.

To get a better estimate of the chance of occurrence of the largest space storms over many solar cycles, researchers need to go back further in time. The aa geomagnetic index used in this study is derived from two stations in UK and Australia. By being on the opposite ends of the Earth, they cancel out the earth’s own background field. The data from this index goes back over 14 solar cycles, or 150 years, but has poor resolution.

Using annual averages of the top few percent of the aa index the researchers found that a ‘severe’ super-storm occurred in 42 years out of 150 (28%), while a ‘great’ super-storm occurred in 6 years out of 150 (4%) or once in every 25 years. As an example, the 1989 storm that caused a major power blackout of Quebec was a great storm.

In 2012 the Earth narrowly avoided trouble when a coronal mass ejection from the Sun missed the Earth and went off in another direction. According to satellite measurements, if it had hit the Earth it would have caused a super-storm.

This post was originally published on the University of Warwick website.