The Sun’s Magnetic Field Is About to Reverse

The Sun is about to experience a crucial event: the reversal of its magnetic field. This event, which occurs approximately every eleven years, marks a significant step in the solar cycle and directly influences solar activity and space weather conditions. Understanding this phenomenon is therefore essential to assess its potential impact on our planet and beyond.

The solar cycle

The solar cycle is a periodic phenomenon of about eleven years during which the magnetic activity of the Sun varies. This cycle is mainly observed through sunspots which are areas of the solar surface where the intensity of the magnetic field is higher, which reduces the local temperature and makes these areas visible as dark spots. The solar cycle begins with a phase of solar minimum where the number of sunspots is relatively low. This phase is followed by a gradual increase in solar activity, culminating in the solar maximuma period when the number of sunspots is at its peak. Then, solar activity decreases again until the next solar minimum.

The Hale cycle and magnetic field reversal

THE Hale cycle is a longer solar magnetic cycle, about twenty-two years long, named after George Ellery Hale who discovered it in the early twentieth century. This cycle consists of two regular solar cycles (eleven years each). What distinguishes the Hale cycle is that during this period, the Sun’s magnetic field changes polarity and returns to its initial orientation. During the first half of the Hale cycle, the solar magnetic field behaves in such a way as to create a dipolewith a well-defined magnetic north and south pole, similar to the Earth’s magnetic field. This is a phase of solar minimum with a relatively stable state of magnetic field. As the Hale cycle progresses towards its maximum, the Sun’s internal magnetic interactions become more complex, leading to a decrease in the clear separation between the north and south poles. The Sun’s magnetic field eventually reverses completely at the end of the Hale cycle, switching from one dipole to another with opposite magnetic polarity. We are currently on a trajectory towards the next solar maximum, expected between end of 2024 and beginning of 2026. During this period, solar activity, measured by the number and complexity of sunspots as well as solar flares, should therefore reach its peak. Chronologically, this means that the reversal of the solar magnetic field will occur a few years later. The next polarity change will be from the north magnetic field to the south magnetic field in the northern hemisphere and vice versa in the southern hemisphere.
Loops of plasma wrap around the sun along magnetic field lines. Credits: Eduardo Schaberger Poupeau

The impact of inversion on Earth

The reversal of the solar magnetic field can have several impacts on Earth. First, the Earth’s magnetic field acts as a protective shield against cosmic radiation, high-energy particles from space. When the solar magnetic field reverses, the Earth’s magnetic field can then momentarily become weaker and less efficient to deflect this radiation. This can increase radiation exposure for living organisms on Earth as well as for electronic equipment in orbit. Reversals of the solar magnetic field also affect the formation of polar auroras by changing the configuration of the Earth’s magnetic field lines. This thus influences the location and intensity of the polar auroras. Disturbances in the Earth’s magnetic field during periods of inversion can also interfere with radio signals by disrupting their propagation through the Earth’s ionosphere. This can thus affect the accuracy of positioning and navigation systems used around the world. Finally, although the precise mechanisms are not fully understood, some studies suggest that variations in solar activity, including magnetic field reversals, could have implications for terrestrial climate models. Fluctuations in solar activity could indeed influence the distribution of solar energy reaching Earth, which could potentially play a role in long-term climate variations. Scientists are also closely monitoring the reversal of the solar magnetic field to understand its implications for the next solar cycle. How quickly the magnetic field returns to a dipole configuration will indeed give clues about the expected intensity of the next cycle. A rapid reversal could indicate an active cycle, while a slower reversal could predict a quieter cycle.