This is well known that a solar storm, depending on its intensity, may affect the functioning of electrical networks, navigation systems or satellite communications. The problem is that it’s not clear what would happen today if the storm’s intensity reached levels comparable to the so-called Carrington event of 1859, one of those extremely occasional phenomena that occur only once every thousand years. Recent testshowever, it suggests that the effects may be even more solemn than scientists thought.
Solar storms form when the solar wind – a continuous stream of charged particles emitted by the Sun – interacts with Earth’s magnetosphere. During the Carrington event, telegraph communications broke down halfway around the world and the aurora borealis were perceptible across North America and as far away as Cuba. In today’s world, severe solar storms can have wider effects and even change the upper atmosphere.
“Our planet’s magnetic field is really great at protecting us from many of the effects of space weather, so they often just appear as disturbances or beautiful aurora borealis,” notes Maria Walach, a researcher at the University of Lancaster who collaborated on the research. “However, there are extreme cases where satellites unexpectedly fall back to Earth or we lose communications and GPS signals.”
To estimate the intensity of the solar wind, researchers primarily utilize measurements taken by satellites located at the Lagrangian point L1, about 1.5 million kilometers from Earth. The problem is that these observations do not exactly match the environment in which the solar wind ultimately interacts with the Earth’s magnetic field. A variable amount of time passes between these two points, and the solar plasma also changes during its journey.
The authors argue that this uncertainty is not merely experimental noise but introduces a systematic bias into the data analysis.
Solar statistics
The centerpiece of the study is a well-known statistical phenomenon called regression to the mean. Simply put, when a measurement is extremely high, the true value it is trying to represent is, on average, less extreme. This is because random uncertainties can sometimes exaggerate an observation.
In the case of the solar wind, the exceptionally intense measurement taken at L1 probably corresponds to a slightly less intense solar wind as it reaches the region where it actually interacts with the magnetosphere. If scientists directly link this extreme measurement to the observed Earth response, the effect will be negligible compared to such a huge stimulus. Repeated thousands of times, this effect creates the false impression that the magnetosphere stops responding as the intensity of the solar wind increases.
What has happened is that for years scientists believed that there was a natural limit to the intensity with which the Earth responded to the most extreme solar storms. According to this concept, when the solar wind reaches very high values, the Earth’s magnetic field stops responding proportionally and its response enters a kind of “saturation”. But a recent study suggests that perhaps that boundary never existed. What appeared to be a physical phenomenon may actually have been an illusion caused by the way the measurements were analyzed.
To test this hypothesis, scientists developed a statistical model that takes into account the main sources of uncertainty: changes in the time it takes the solar wind to reach Earth and the random changes it undergoes during its journey. The model reproduces with extraordinary accuracy the same “saturation” curve observed in over 25 years of data, without having to resort to any physical mechanism that limits the Earth’s response.
They then used a technique known as regression calibration, which mathematically corrects for the bias caused by measurement uncertainty. After this correction, the alleged saturation disappears almost completely. The relationship between solar wind intensity and geomagnetic response becomes essentially linear again, at least to the extent for which there are a sufficient number of recorded observations – more than a million, in fact.
No limit
What are the implications of these results, as published in the journal Nature? If Earth’s response continues to boost proportionally during catastrophic events, an extreme solar storm like the Carrington event could be much more unsafe than previously thought. The authors estimate that for very high solar wind values, the geomagnetic impact could be approximately twice as huge as calculated in classic models.
“If there is no upper limit to our planet’s response to solar wind, extreme case modeling must take this into account, and we should remain vigilant about the effects of space weather.” – Walach said in a press note. “Fortunately, these very extreme cases are rare, but that also means we have limited data to work with and only time will tell what will happen in the event of a very extreme, once-in-a-millennium event.”
The study did acknowledge this limitation: there are still very few records of the most extreme episodes. For this reason, researchers do not claim that satiation is impossible. Rather, they argue that the available data do not provide convincing statistical evidence for its existence.
This story originally appeared on WIRED in Spanish and was translated from Spanish.