Dynamic Sun - Magnetic Forces Shaping Solar Phenomena

In drawings and paintings the sun often appears as a perfect circle of light, projecting its energy equally in all directions. However, if we look closer we observe occasional eruptions in specific directions. Solar eruptions occur when the energy stored in the sun’s magnetic field discharges suddenly, rapidly heating matter in its vicinity to a temperature of millions of degrees. This results in a release of a vast amount of energy across the entire electromagnetic spectrum: from gamma rays to x-rays and to radio waves. While our atmosphere shields us from harmful radiation, when these emissions of radiation reach Earth, they can disrupt media broadcasts. But this brings us to an intriguing question - why does the sun have a magnetic field?  

Solar eruptions occur when energy stored in the sun’s magnetic field is suddenly discharged. A solar eruption documented in July 2022 | Miguel Claro / Science Photo Library

The sun is a giant plasma sphere that rotates on its axis. The surface temperature on the sun is lower than the temperature within it. The temperature differences cause hot matter from deeper layers to rise while colder matter from the outer layers descends - a process known as convection, which is also responsible for the swirling motion of boiling water in a kettle. The complex motion of the charged plasma particles, driven by convection and the sun’s axial rotation generates magnetic fields, which in turn have an effect on the motion of the charged particles. The complex motion that is caused by the combination of convection, the sun’s spin - which is different at varying speeds across latitude lines on its surface - and the local magnetic fields contribute to the intricate dynamics of the sun's magnetic field. In fact, the depth at which the sun's magnetic field originates remains a subject of ongoing research.

The complex motion that is caused by the intricate interplay of convection, the sun’s differential rotation - varying at different latitude lines on the sub's surface - and local magnetic fields creates the highly complex magnetic field of the sun. A model illustrating the sun’s magnetic field | NASA's Scientific Visualization Studio - 

 A video by NASA detailing the changes in the sun’s magnetic field:

Three Millenia Of Sun Monitoring 

The first documented observation of sunspots dates back to the Chinese  “Book of Changes” ( I Ching), written over 2,800 years ago. Starting from the 28th century B.C. Chinese astronomers methodically documented sunspots. 

The first recorded report of sunspots in the Western world was by the Greek philosopher Theophrastus, around 300 B.C. The first to observe sunspots through a telescope - or atleast, the first to document it, was English astronomer Tomas Harriot in December 1610. In 1775, Danish astronomer Christian Horrebow noticed that sunspot numbers and sizes change in a cycle of a few years. In an article published in 1801, British astronomer William Herschel claimed to have found a link between the number and shape of sunspots and the temperature measured on the surface of the Earth, and even between the number of sunspots and wheat prices in Britain. However, these claims were later disproven. In 1843 German astronomer Heinrich Schwabe presented a clear cycle in the average number of sunspots, while in 1852 Swiss astronomer Rudolf Wolf established a numbering system for solar cycles, dating back to mid-18th century, with the cycle that began in 1755 considered as the first cycle in the count. The average duration of a solar cycle is approximately eleven years and it is defined as the period between two periods of low solar activity.   

The first documented observation of a sunspot appears in the Chinese “Book of Changes”, written over 2,800 years ago. A photo of sunspots | Claus Lunau / Science Photo Library

By analyzing the frequency of the carbon 14 isotope in tree rings, in 2004 scientists successfully reconstructed solar activity levels for the past 11,400 years, since the last ice age. The researchers found that during ninety percent of this prolonged period, the level of solar activity was lower than that observed between the 1940’s and the early 2000’s, and nearly all previous periods of enhanced activity were shorter than this period. In the last solar cycle, cycle number twenty four, that lasted from December 2008 to December 2019, solar activity was significantly lower than what was considered usual in recent decades, similar to the levels documented between the late 19th century and the early 20th century. 

Is there a link between solar activity levels and global warming on Earth? Most researchers believe that the sun’s contribution to the observed warming trend in recent decades is insignificant.  For instance, despite Earth experiencing a gradual warming since the mid-20th century, the intensity of solar radiation reaching us has remained relatively stable since at least the mid-19th century. Moreover, if solar activity were the main driver of global warming, we would expect warming across all layers of the atmosphere, whereas the upper atmosphere is actually exhibiting a cooling trend.

The average duration of a solar cycle is eleven years, defined as the period of time between two periods of low solar activity. A graph illustrating the cyclical nature of sunspots 

When charged particles from solar wind collide with molecules in the upper layers of the atmosphere, they emit light, known as the “northern lights”. A spectacular display of northern lights over Alaska | Wikipedia, United States Air Force.