A new study led by NASA has challenged one of the core concepts in modern space weather. The authors of the research, published in the journal Nature, concluded that Earth’s magnetosphere does not stop amplifying its response to extremely powerful solar wind, as had been believed for decades.
If this conclusion is confirmed, the destructive impact of the strongest solar storms on satellites, communications, and power grids could be about twice as high as current estimates.
Until now, it was thought that once solar wind reaches a certain intensity, geomagnetic activity plateaus—further increases in plasma flow barely boost currents in the upper atmosphere. Around ten physical theories were proposed to explain this effect. However, the authors of the new study argue that this “saturation” is actually a result of statistical distortion rather than a real physical process.
The error stems from measurements of solar wind taken at the Lagrange point L1, located about 1.5 million km from Earth. This is where spacecraft record parameters of the charged particle stream. As it travels toward Earth, the solar wind changes, and additional inaccuracies arise from errors in determining when the plasma arrives, shifts in its structure, and the instruments’ own measurement errors.
As a result, the actual parameters of the solar wind near the magnetosphere differ from those recorded at L1.
The authors explained the observed “saturation” as an effect of regression toward the mean—a statistical phenomenon where extreme measurements, due to random errors, end up inflated relative to true values. This creates a false impression that during the most powerful events, the magnetosphere begins to respond more weakly, even though the relationship remains linear and continues to rise.
To test this hypothesis, the scientists used a new statistical model that accounts for measurement errors and their varying magnitude across different levels of solar activity. Additionally, they analyzed data from NASA’s THEMIS and MMS spacecraft, which operate much closer to Earth than the L1 point. After statistical calibration, the relationship between solar wind strength and geomagnetic response in the data no longer plateaued but maintained a linear trend up to the highest recorded values. A similar result was obtained for indices indicating the intensity of electric currents in the upper atmosphere above Earth’s polar regions.
If these findings are confirmed by observations, existing models of space weather and theories explaining the intensification of geomagnetic storms will need revision. This means that risk assessments for satellites, communication systems, and power grids during extreme solar events may be significantly underestimated, as the magnetosphere likely lacks the previously assumed “natural limit” in its response to the most powerful solar wind outbursts.
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