Rapid changes between solar seasons solved by the new solar clock

Violent activity on our Sun results in some of the most extreme space weather events on Earth, affecting systems such as satellites, communications systems, power distribution, and aviation. The approximately 11-year solar activity cycle has three “seasons”, each of which affects the space weather experienced on Earth differently: (i) solar maximum, the sun is active and disordered, when space weather is stormy and events are irregular (ii) the decline phase, when the sun and solar wind become ordered, and space weather is more moderate and (iii) the solar minimum, when activity is calm.

In a new study conducted by the University of Warwick and published in The Journal of Astrophysics, scientists found that the transition from the solar maximum to the waning phase is rapid, occurring within a few solar rotations (27 days). They also showed that the waning phase is twice as long in even solar cycles than in odd cycles.

No two solar cycles are identical in amplitude or duration. To study the solar seasons, scientists built a solar clock from the daily record of the number of sunspots available since 1818. This maps irregular solar cycles to a regular clock. The sun’s magnetic polarity reverses after each solar cycle of about 11 years, resulting in a magnetic cycle of about 22 years (named after George Ellery Hale) and to explore this a 22-year clock was built . The effect on space weather on Earth can be tracked using the longest continuous records of geomagnetic activity over the past 150 years, and once the clock is built, it can be used to study multiple observations of the activity. seasonal solar effects that affect the Earth.

With the greater detail provided by the solar clock, scientists were able to see that the transition from the solar maximum to the waning phase is rapid, occurring within a few solar rotations (27 days). There was also a marked difference in the duration of the waning phase when the sun’s magnetic polarity is “high” versus “low”: in even cycles, it is about twice as long as odd cycles. As we are about to enter Cycle 25, scientists predict that the next phase of decline will be short.

Lead author Professor Sandra Chapman from the Department of Physics at the University of Warwick said that “by combining well-known methods in a new way, our clock resolves changes in the Sun’s climate to within a few rotations. Then you find that the changes between certain phases can be really sharp.

“If you know you’ve had one long cycle, you know the next one will be short, we can estimate how long it’s going to be. Knowing the calendar of climatic seasons helps plan space weather. Operationally, it is. is useful for knowing when conditions will be active or calm, for satellites, power grids, communications. “

The results also provide a clue to understanding how the Sun reverses polarity after each cycle.

Professor Chapman adds that “I also think it’s remarkable that an object the size of the sun can shift its magnetic field every 11 years, and going up is different from going down. ‘, and it’s an intriguing problem, at the heart of how the sun generates its magnetic field. ”