In recent weeks, solar activity and the auroras that are also visible in our region have been in the headlines again and again. In the coming months, the sun's activity will continue to increase and "space weather" will remain a topic. The sun is the source of all life, but it also poses a certain threat to our now highly technological world.
Danger from outer space
Most of us probably intuitively think of an asteroid impact, which has also been the subject of a number of films. However, another danger also comes from our sun. Its activity is subject to certain cycles, it has its own rhythm and pulse. We are currently in the ascending branch of the 25th solar cycle. At the beginning of this cycle, forecasts predicted a maximum between November 2024 and March 2026. However, solar activity in recent months has always been slightly above the modeled course, which is why the forecasts have now been adjusted slightly. The maximum of the current cycle is now expected between January and October 2024, which has been brought forward. The expected maximum number of sunspots has also been adjusted slightly upwards and is now between 137 and 173. The maximum number of spots during the maximum of the 24th cycle was only 119; the long-term average number of spots during such a maximum is 179. The sun's behavior is permanently monitored from Earth and with a number of space probes. If a coronal mass ejection (CME) occurs, it can now be easily categorized.
Fig. 1: Coronal mass ejection on August 31, 2012; Source: Wikipedia
There is then a warning time of a few hours to a few days, depending on the direction and speed of the plasma cloud. Stronger events cause disruption to radio traffic and satellites are at risk. However, extreme solar storms have also occurred in the past; statistically, they happen about once every 500 years. Would our modern world be prepared for something like this?
Carrington event
This was the strongest geomagnetic storm observed and documented to date. It took place between August 28 and September 4, 1859 and was a combination of several individual events. On the morning of August 28, the first strong coronal mass ejection occurred. It initially went unnoticed, as the sun was below the horizon for the magnetometer at Kew Observatory in London (probably the only one in the world at the time). In the late evening of August 28, there were massive auroras in the northern hemisphere, which could even be seen in the Caribbean. There were also severe disruptions to telegraph traffic.
Another event occurred on September 1 at around 11:20 UTC . A large group of spots was centered on the sun and was observed and documented at this time by astronomer Richard Carrington (1826-1875) . He saw a strong burst of white light within the group of spots, a super-flare. This event was also recorded by the magnetometer mentioned above. The plasma cloud moved towards the Earth at 2000 km/s and reached it after just over 17 hours. This second event surpassed the first one on August 28, and auroras could be observed in regions far to the south. The Earth's magnetic field was massively disturbed, and the currents induced in the telegraph lines caused sparks – and some of the paper strips were set on fire.
Fig. 2: Sunspots and flares on September 1, 1859, drawn by Richard Carrington; Source: Wikipedia
Extreme solar storm 2012
According to a report published by NASA in 2014, there was an eruption on the sun on July 23, 2012, which was comparable in intensity to that of 1859. Daniel Baker from the University of Colorado describes the storm as "at least as strong". However, the Earth was lucky! Although the plasma cloud hit the Earth's orbit, the Earth itself had already moved out of the actual line of fire. A few days earlier and the Earth's magnetic field and our civilization would have been severely tested. However, the cloud of charged particles hit the solar observation probe STEREO-A(Solar TErrestrial RElations Observatory), which was able to record data and survived the event unscathed.
Fig. 3: Three-dimensional observation of solar flares by the STEREO A and B probes; Source: Wikipedia
Possible effects
Auroras are one of the beautiful effects of the omnipresent solar wind. During strong solar storms, the Earth's magnetic field is compressed on the side facing the sun. In extreme events, it can be severely weakened, and currents would be induced in cables and other long metal bodies such as pipelines. Models and simulations now exist for such scenarios. The induced currents would cause fires in transformers, resulting in large-scale power outages. Telecommunications would collapse after a certain period of time. Large transformers are not easy to repair or replace, their construction and transportation is costly and also requires electricity. In any case, such an extreme solar storm would hit our technologized world hard, and the next"super flare" is only a matter of time. Will it happen in this cycle or in the next one?
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