Geomagnetic field protects Earth from electron showers

Tohoku University geophysicist Yuto Katoh led a study into the activity of high energy electrons and clarified the unexpected role of the geomagnetic field surrounding the Earth in protecting.

Understanding the ionosphere high in the Earth's atmosphere is important due to its effects on communications systems, satellites and crucial chemical features including the ozone layer. New insights into the activity of high energy electrons have come from a simulation study led by geophysicist Yuto Katoh at Tohoku University, reported in the journal Earth, Planets and Space.

"Our results clarify the unexpected role of the geomagnetic field surrounding the Earth in protecting the atmosphere from high energy electrons," says Katoh.

The ionosphere is a wide region between roughly 60 and more than 600 kilometers above the Earth's surface. It contains electrically charged particles that are a mixture of ions and free electrons generated by the interaction of the atmosphere with radiation from the sun.

Polar regions of the ionosphere are subjected to a particularly steady and energetic stream of incoming electrons in a process called electron precipitation. These 'relativistic' electrons move at close to the speed of light, where the effects of Einstein's relativity theory become ever more significant. They collide with gas molecules and contribute to many phenomena in the ionosphere, including colourful auroral displays. The processes are heavily influenced by the effects of the geomagnetic field on the charged particles involved.

The Tohoku team, with colleagues in Germany and other institutions in Japan, developed a sophisticated software code that focused particular attention on simulating the effects of a relatively unstudied 'mirror force' on the electron precipitation. This is caused by the magnetic force acting on charged particles under the influence of the geomagnetic field.

The simulations demonstrated how the mirror force causes relativistic electrons to bounce back upwards, to an extent dependent on the angles at which the electrons arrive. The predicted effects mean that electrons collide with other charged particles higher in the ionosphere than previously suspected.

Illustrating one example of the significance of this work, Katoh comments: "Precipitating electrons that manage to pass through the mirror force can reach the middle and lower atmosphere, contributing to chemical reactions related to variations in ozone levels." Decreased ozone levels at the poles caused by atmospheric pollution reduce the protection ozone offers living organisms from ultraviolet radiation.

Katoh emphasizes the key theoretical advance of the research is in revealing the surprising significance of the geomagnetic field and the mirror force in protecting the lower atmosphere from the effects of electron precipitation activities by keeping them further away.

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Scientists report 'benchmarks' for extreme space weather

High-energy 'relativistic' electrons -- so-called "killer" electrons -- are a major source of radiation damage to satellites and so understanding their patterns of activity is crucial. Bursts of charged particles and magnetic fields from the Sun can tear open the Earth's magnetic field, giving rise to geomagnetic storms. During these events the number of killer electrons in the outer radiation belt can increase by orders of magnitude and become a significant space weather hazard.

Dr Nigel Meredith of BAS led an international team who analysed 20 years of data from a US GPS satellite to determine the 1 in 10, 1 in 50, and 1 in 100-year event levels. A 1 in 100-year event is an event of a size that will be equalled or exceeded on average once every 100 years.

Satellite operators, manufacturers, insurers, and governments need to prepare and mitigate against the risks posed by these electrons. Society is increasingly reliant on satellites for a variety of applications including communication, navigation, Earth observation and defence. As of April 2022, there were 5,465 operational satellites in Earth orbit, and most are exposed to energetic electrons for at least some of their orbit. In 2021, the overall global space economy generated revenues of $386 billion, an increase of four percent compared to the previous year.

Dr Nigel Meredith, space weather scientist and lead author of the study says:

"The 1 in 100 year event levels reported in this study are important for industry and government. They serve as benchmarks against which to compare other extreme space weather events and to assess the potential impact of an extreme event."

These findings are vitally important to the satellite industry as engineers and operators require realistic estimates of the largest electron fluxes encountered in GPS orbit to prepare for the impacts of these extreme events and to improve the resilience of future satellites. The findings are essential for satellite insurers to help them ensure satellite operators are doing all they can to reduce risk and to evaluate realistic disaster scenarios

The difference between the 1 in 10 year and 1 in 100-year event varies depending on the energy of the electrons and the distance from Earth. These differences are largest at the highest energies furthest from the planet, varying between a factor of 3 and 10 for some of the highest electron energies over 35,000 km from the Earth's surface. Such substantial increases could pose a significant additional risk to satellites operating in this region.

Like weather on our planet, space weather can vary greatly over minutes, days, seasons and the 11-year solar cycle. The researchers found that the majority of these killer electron events occurred during the solar cycle's declining phases -- seen twice during the 20-year period they studied -- but the largest event was elsewhere, showing that extreme events can happen at any time.

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Biblical military campaigns reconstructed using geomagnetic field data

A joint study by Tel-Aviv University and the Hebrew University, involving 20 researchers from different countries and disciplines, has accurately dated 21 destruction layers at 17 archaeological sites in Israel by reconstructing the direction and/or intensity of the Earth's magnetic field recorded in burnt remnants. The new data verify the Biblical accounts of the Egyptian, Aramean, Assyrian, and Babylonian military campaigns against the Kingdoms of Israel and Judah.

Findings indicate, for example, that the army of Hazael, King of Aram-Damascus, was responsible for the destruction of several cities -- Tel Rehov, Tel Zayit, and Horvat Tevet, in addition to Gath of the Philistines, whose destruction is noted in the Hebrew Bible. At the same time, the study refutes the prevailing theory that Hazael was the conqueror who destroyed Tel Beth-Shean. Other geomagnetic findings reveal that the cities in the Negev were destroyed by the Edomites, who took advantage of the destruction of Jerusalem and the Kingdom of Judah by the Babylonians.

The groundbreaking interdisciplinary study was published in the Proceedings of the National Academy of Sciences (PNAS) and is based on the doctoral thesis of Yoav Vaknin, supervised by Prof. Erez Ben-Yosef and Prof. Oded Lipschits of TAU's Institute of Archaeology and Prof. Ron Shaar from the Institute of Earth Sciences at the Hebrew University.

The researchers explain that geophysicists, attempting to understand the mechanism of earth's magnetic field, track changes in this field throughout history. To this end they use archaeological findings containing magnetic minerals which, when heated or burned, record the magnetic field at the time of the fire. Thus, in a 2020 study, researchers reconstructed the magnetic field as it was on the 9th of the month of Av, 586 BCE, the Hebrew date of the destruction of the First Temple and the City of Jerusalem by Nebuchadnezzar and his Babylonian army. Now, using archaeological findings unearthed over several decades at 17 sites throughout Israel, alongside historical information from ancient inscriptions and Biblical accounts, the researchers were able to reconstruct the magnetic fields recorded in 21 destruction layers. They used the data to develop a reliable new scientific tool for archaeological dating.

Yoav Vaknin explains: "Based on the similarity or difference in intensity and direction of the magnetic field, we can either corroborate or disprove hypotheses claiming that specific sites were burned during the same military campaign. Moreover, we have constructed a variation curve of field intensity over time which can serve as a scientific dating tool, similar to the radiocarbon dating method."

One example given by the researchers is the destruction of Gath of the Philistines (identified today as Tel Tzafit in the Judean foothills) by Hazael, King of Aram-Damascus. Various dating methods have placed this event at around 830 BCE, but were unable to verify that Hazael was also responsible for the destruction of Tel Rehov, Tel Zayit and Horvat Tevet. Now the new study, identifying full statistical synchronization between the magnetic fields recorded at all of these four sites at the time of destruction, makes a very strong case for their destruction during the same campaign. A destruction level at Tel Beth-Shean, on the other hand, recording a totally different magnetic field, refutes the prevailing hypothesis that it too was destroyed by Hazael. Instead, the magnetic data from Beth-Shean indicate that this city, along with two other sites in northern Israel, was probably destroyed 70-100 years earlier, a date which could correspond with the military campaign of the Egyptian Pharaoh Shoshenq. Shoshenq's campaign is described in the Hebrew Bible and in an inscription on a wall of the Temple of Amun in Karnak, Egypt, which mentions Beth-Shean as one of his conquests.

One of the most interesting findings revealed by the new dating method has to do with the end of the Kingdom of Judah. Prof. Erez Ben Yosef: "The last days of the Kingdom of Judah are widely debated. Some researchers, relying on archaeological evidence, argue that Judah was not completely destroyed by the Babylonians. While Jerusalem and frontier cities in the Judean foothills ceased to exist, other towns in the Negev, the southern Judean Mountains and the southern Judean foothills remained almost unaffected. Now, the magnetic results support this hypothesis, indicating that the Babylonians were not solely responsible for Judah's ultimate demise. Several decades after they had destroyed Jerusalem and the First Temple, sites in the Negev, which had survived the Babylonian campaign, were destroyed -- probably by the Edomites who took advantage of the fall of Jerusalem. This betrayal and participation in the destruction of the surviving cities may explain why the Hebrew Bible expresses so much hatred for the Edomites -- for example, in the prophecy of Obadiah."

Prof. Oded Lipschits adds: "The new dating tool is unique because it is based on geomagnetic data from sites, whose exact destruction dates are known from historical sources. By combining precise historical information with advanced, comprehensive archaeological research, we were able to base the magnetic method on reliably anchored chronology."

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Earth's magnetic poles not likely to flip anytime soon

The emergence of a mysterious area in the South Atlantic where the geomagnetic field strength is decreasing rapidly, has led to speculation that Earth is heading towards a magnetic polarity reversal. However, a new study that pieces together evidence stretching back 9,000 years, suggests that the current changes aren't unique, and that a reversal may not be in the cards after all. The study is published in PNAS.

The Earth's magnetic field acts as an invisible shield against the life-threatening environment in space, and solar winds that would otherwise sweep away the atmosphere. However, the magnetic field is not stable, and at irregular intervals at an average of every 200,000 years polarity reversals happen. This means that the magnetic North and South poles swap places.

During the past 180 years, Earth's magnetic field strength has decreased by about 10 percent. Simultaneously, an area with an unusually weak magnetic field has grown in the South Atlantic off the coast of South America. This area, where satellites have malfunctioned several times due to exposure to highly charged particles from the sun, is called the South Atlantic Anomaly. These developments have led to speculation that we may be heading for a polarity reversal. However, the new study suggests this may not be the case.

"We have mapped changes in the Earth's magnetic field over the past 9,000 years, and anomalies like the one in the South Atlantic are probably recurring phenomena linked to corresponding variations in the strength of the Earth's magnetic field," says Andreas Nilsson, geologist at Lund University.

The results are based on analyzes of burnt archaeological artefacts, volcanic samples and sediment drill cores, all of which carry information about the Earth's magnetic field. These include clay pots that have been heated up to over 580 degrees Celsius, volcanic lava that has solidified, and sediments that have been deposited in lakes or in the sea. The objects act as time capsules, and carry information about the magnetic field in the past. Using sensitive instruments, the researchers have been able to measure these magnetizations and recreate the direction and strength of the magnetic field at specific places and times.

"We have developed a new modeling technique that connects these indirect observations from different time periods and locations into one global reconstruction of the magnetic field over the past 9,000 years," says Andreas Nilsson.

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