Thinning of the Sun's magnetic layer: the peculiar solar minimum could have been predicted

TL;DR

The paper demonstrates that analyzing solar oscillation data can reveal early signs of an unusually deep solar minimum, suggesting it could have been predicted based on subsurface structural changes before the minimum occurred.

Contribution

It introduces a method to predict unusual solar minima by examining changes in the Sun's subsurface layers through oscillation frequency data.

Findings

Deep minimum in cycle 24 was preceded by distinct subsurface changes.

Changes during cycle 23 were localized above 0.996Rsun, shallower than in cycle 22.

Data analysis could have predicted the unusual depth of the solar minimum.

Abstract

The solar magnetic activity cycle causes changes in the Sun on timescales that are relevant to human lifetimes. The minimum in solar activity that preceded the current solar cycle (cycle 24) was deeper and quieter than any other recent minimum. Using data from the Birmingham Solar-Oscillations Network (BiSON), we show that the structure of the solar sub-surface layers during the descending phase of the preceding cycle (cycle 23) was very different from that during cycle 22. This leads us to believe that a detailed examination of the data would have led to the prediction that the cycle-24 minimum would be out of the ordinary. The behavior of the oscillation frequencies allows us to infer that changes in the Sun that affected the oscillation frequencies in cycle 23 were localized mainly to layers above about 0.996Rsun, depths shallower than about 3000 km. In cycle 22, on the other hand, the changes must have also occurred in the deeper-lying layers.