Activity on the Sun is increasing. This can also be felt on earth. Most recently due to the increased occurrence of northern lights over northern Germany. But the solar storms could also destroy many important areas on Earth, such as the power supply.
After a solar storm, beautiful polar lights could also be seen in northern Germany recently. The solar flares underlying such storms can also result in the destruction of satellites and large-scale power failures on Earth. "There are also indirect effects, such as the extremely precise satellite time signal used in medical technology or in ultra-fast stock exchange trading," says Jens Berdermann from the German Aerospace Center (DLR) in Neustrelitz. Since satellite applications are now common in many areas, solar storms can lead to a variety of disruptions.
The number and strength of such events depend on the activity of the sun - which is once again approaching a maximum in a cycle of about eleven years. It could be achieved in the years 2024 to 2026. Predicting space weather, which is mainly due to radiation, particles and magnetized plasma from the sun, is therefore likely to become increasingly important in the coming period. But forecasts are considerably more difficult than with the weather on earth.
Despite scientific progress and large amounts of data, comparatively little is known about our central star, says Volker Bothmer from the University of Göttingen, who wrote his doctoral thesis on solar storms in the early 1990s and has since devoted himself to researching the sun and space weather.
"For example, we don't know why the temperatures in and on the sun are distributed in the way we model and measure them," explains Svetlana Berdyugina from the Leibniz Institute for Solar Physics in Freiburg. In the center there are about 15 million degrees, on the sun's surface just under 6000 degrees, while the sun's atmosphere, also called the corona, can be up to two million degrees hot.
Berdyugina's central research topic is the magnetic field of the sun and other stars. Local changes in the Sun's strong magnetic field are what cause solar flares to eject radiation and charged particles into space.
While the earth's magnetic field has fairly smooth transitions between the magnetic poles and the equator, the sun's magnetic field is much more complex. On the one hand, this is due to convection, i.e. the circulation of the hot plasma in the sun. On the other hand, different areas of the hot ball of gas rotate around their own axis at different speeds: at the equator, the full rotation is completed after around 25 days, near the poles it takes around 31 days. Depending on the latitude, deeper layers also rotate faster or slower than the surface. This leads to turbulent eddies in the solar magnetic field.
"It is very difficult to simulate the changes in the sun's magnetic field because you need large computing capacities for this," emphasizes Berdyugina. The computing capacity was far from sufficient for a simulation of the entire sun. Therefore, sections of the sun must be simulated in such a way that meaningful statements can be made.
The researcher dares not predict when solar storms can be reliably predicted. It may also be necessary to use artificial intelligence to search through existing data for patterns in order to find harbingers of solar storms. An early prediction would be important, among other things, in order to be able to protect at least part of the vulnerable infrastructure in good time.
In the past few decades, the sun has never shown its destructive potential to the full extent - but it can be guessed from the consequences of the so-called Carrington event. "The Carrington event was about three times as strong as the 30 strongest solar storms that we have recorded since 1932," says Volker Bothmer.
In early September 1859, the telegraphs in Northern Europe and North America went haywire: employees received electric shocks if they touched them. In some offices, sparks erupted from the device and ignited paper on which the telegrams were written. Even after the telegraphs were switched off, when they should have been dead, they were still charged enough for telegrams to be sent. The events triggered fear and horror - and severely affected the worldwide telegraph network, which was only built up in previous years. In addition, auroras, which usually only appear in the north or south polar regions, were suddenly visible even in the tropics - including the Bahamas, Hawaii and Jamaica.
Earlier, on September 1, the English astronomer Richard Carrington (1826-1875) had spotted two bright flashes of light on the Sun when he cast their telescopic image onto a screen to delineate sunspots. At that time nobody knew that all events were due to one cause: the strongest solar storm recorded by humans so far.
"If you consider how many electrical devices there are now, you can reasonably imagine what a Carrington event would trigger today," says DLR scientist Berdermann. The DLR team observes space weather and investigates its influence on important technologies such as navigation and communication via satellite and the power grid.
What exactly happens during solar bursts? When the sun's magnetic field lines break up, high-energy particles escape first, primarily protons. Some travel at about 15 percent of the speed of light and reach Earth in about an hour. Because the burst occurs in the solar corona, another portion of the particles impact the sun's surface, emitting X-rays -- called an X-ray flash or flare. This radiation travels at the speed of light and reaches Earth after about eight minutes.
An important occasional consequence of a solar flare is the so-called coronal mass ejection, which consists of electrons, protons and atomic nuclei. It can reach speeds of over 2000 kilometers per second and usually arrives on Earth after one or two days. The fastest solar storms reach Earth in less than a day, for example the Carrington event took 17 hours.
The plasma is mainly responsible for the effects of solar storms: Because the components are electrically charged, they interact with the earth's magnetic field and compress it, as it were. Magnetic short-circuits in the tail of the earth's magnetic field produce streams of particles in the polar regions, which stimulate the air particles to glow, which becomes visible as auroras.
The disturbance of the earth's magnetic field also produces a geomagnetically induced current in long lines. It is true that the strengths of the resulting electrical fields are considerably lower than the local fields from a lightning strike. However, high voltages and high currents can flow along the length of an overhead power line or pipeline, destroying transformers and causing blackouts.
Furthermore, the plasma heats the upper atmosphere, which extends to the orbits of satellites and slows them down due to the increased friction. In some cases, orbit corrections have to be made, but in other cases the operators can also lose control of their satellites, which eventually crash.
Even minor disturbances can have an impact: With satellite navigation, the device on the ground determines its location based on the propagation times of several satellite signals. If the orbits of the satellites change even slightly or signals are delayed in the ionosphere, this has consequences for the accuracy of the position determination.
Mankind is not completely helpless: Since the X-ray flash and the high-energy particles reach the earth much earlier than the plasma cloud of a coronal mass ejection, we can at least give a little advance warning before such a cloud arrives. But there is plenty of room for improvement.
In a joint contribution in 2022, Berdermann, the Göttingen researcher Bothmer and other space weather experts recommended, among other things, the establishment of a national space weather center, the establishment and expansion of ground-based and satellite-based observation systems and the preparation of a risk assessment for all affected systems and services. "Particular attention must be paid to the effects on affected systems, in particular ensuring the energy supply (substations, transformers) and emerging new developments such as in the field of autonomous driving and e-mobility," write the scientists.
Internationally, there are a number of efforts for improved solar observation and space weather warning capabilities. At the European Space Agency (ESA), for example, there is the "ESA Vigil" project: in a few years, the satellite is to be placed at the so-called Lagrange point 5, around 150 million kilometers from the sun and from the earth, and to enable early warnings.
Do solar storms also directly threaten human life? On Earth they are quite well protected by the magnetic field, but even when flying in the polar region they can get an increased dose of high-energy particles. It becomes even more dangerous for astronauts who are outside the earth's magnetic field. "That's why space weather is an important factor in moon and Mars missions," emphasizes Bothmer. For example, for a solar storm in 1972 during the US space agency NASA's "Apollo" moon flight program, data evaluations would have shown that it would have been life-threatening for the astronauts if a space flight had taken place at the time of the solar storm.