Humans have been using sunspots to try to define the solar cycle for 400 years. Changes to weather patterns on Earth and occasionally threatening telecommunications are caused by the ebb and flow of solar activity. Predicting these changes reliably could be helpful.
Scientists use the concept of a "solar minimum" to mark the beginning of each cycle. Robert Leamon is a research scientist at the Partnership for Heliophysics and Space Environment Research, a partnership with NASA.
A "solar clock" based on the sun's magnetic field, rather than the presence or absence of sunspots, can accurately describe and predict many key changes in the solar cycle. The sunspot method can't predict solar flares in advance, but the new framework can.
The solar cycle is a sequence of events according to the new research. Changes happen at each one-fifth of a cycle. Regardless of the exact length of the cycle, it's true. They call it a circle of fifths in honor of music lovers.
The landmarks can be found by finding them.
A new paper by Leamon and colleagues at the National Center for Atmospheric Research and Alan Title at the Lockheed Martin Advanced Technology Center builds on work done by Leamon, Daniel Marsh, and Scott McIntosh. The paper showed the existence of a solar cycle phenomenon.
There is overlap between consecutive cycles when the sun's magnetic field is changing. The sun's magnetic field can either point to one of the sun's poles, or the other. When the previous cycle's polar field has completely disappeared from the sun's surface, and is followed by a dramatic rise in solar activity, a terminator is marked.
There are more landmarks along the way through a full solar cycle from terminator to terminator. The landmarks are more consistent than using sunspot as a guide. The max number of sunspots doesn't align with when the polar field reverses, but it happens at one-fifth of the cycle.
There are dark areas at the sun's poles. The last X-flare occurs at three-fifths of a cycle. The sunspot is at a minimum at this landmark. After the sun passes through another terminator, the activity of the sun increases. UV emissions can be seen on the fifths.
Cause and symptoms.
The team was able to pick out patterns in the data. Since 1947, the Dominion Radio Astrophysical Observatory has measured solar radio flux, which is a proxy for solar activity. Magnetic fields on the sun's surface have been measured by the Wilcox Solar Observatory.
The team asked how many different solar things they could look at after they noticed the changes. They all have the same set of fifths. The five landmarks are tied to different parameters on the cycle.
The focus of the sunspot is changed by the theory of a solar clock. It's similar to symptoms and causes. The magnetic field is the root cause of the solar cycle.
There are long threads.
The shift in framework improves the ability of researchers to predict events in the solar cycle more precisely and further in advance, which gives people like satellite operators time to make preparations based on predicted solar activity. The precise length of the first fifth of the cycle is determined after the initial polar field reversal is detected. The timing of the other fifths is simple.
The framework puts tighter bounds on the time when flares are expected, which is useful information for people on Earth. The period from terminator to about three-fifths of a cycle seems to be the peak time for flares, with a rapid drop off after that point. A new framework predicts that the last major flares should occur in the mid-20th century.
"Nature uses only the longest threads to weave her patterns, so that each small piece of her fabric reveals the organization of the entire tapestry," said Richard Feynman. The new theory from Leamon and colleagues is an example of a long thread that makes it easier for humans to be prepared for changes in the sun.
More information: Robert J. Leamon et al, Deciphering Solar Magnetic Activity: The Solar Cycle Clock, Frontiers in Astronomy and Space Sciences (2022). DOI: 10.3389/fspas.2022.886670
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