New research from DTU and partners from NASA's Jet Propulsion Laboratory and the University of New Brunswick shows that eruptions on the Sun's surface not only send bursts of energetic particles into Earth's atmosphere causing disturbances in our planet's magnetic field, they can also strangely decrease the number of free electrons over large areas in the polar region of the ionosphere.
Eruptions on the Sun's surface, also called solar storms, trigger geomagnetic storms and this usually causes disturbances globally in the ionosphere and the magnetosphere, which is the region of the atmosphere governed primarily by Earth's magnetic field.
Now new research shows that these eruptions on the sun's surface not only send bursts of energetic particles into Earth's atmosphere causing disturbances in the magnetic field, but they may also significantly decrease the number of free electrons over large areas in the polar region of the ionosphere -- the ionized part of the upper atmosphere.
"We have conducted extensive measurements associated with a specific geomagnetic storm over the Arctic in 2014, and here we have found that electrons in large quantities were almost vacuumed out from areas that extend over 500 to 1000 kilometres. It happens just south of an area with strong increases in electron density, called patches," said Professor Per Høeg from DTU Space.
The new research has been carried out by the National Space Research Institute at the Technical University of Denmark (DTU Space) and collaborating international partners from NASA's Jet Propulsion Laboratory (JPL) and the University of New Brunswick (UNB).
A surprising mechanism at play
The research indicates that there is a surprising and previously unknown mechanism at play in the geomagnetic storms.
Solar activity usually tends to increase the rate of ionization in the atmosphere and thus the density of free electrons in the ionosphere or to move electrons to the polar caps. The research show that the opposite, a depletion of electrons, can take place.
"It is a surprising discovery; one we had not expected. But now we can see it happening in other data sets from Canada, which indirectly support our new observations," said Per Høeg.
The new research also provides a host of other insights that increases the understanding of how such geomagnetic storms affect Earth's atmosphere and could possibly lead to improved radio communication and navigation throughout the Arctic.
The results of the research have been published in the American Geophysical Union's scientific journal Radio Science and featured on its cover.
The discovery is an important piece of the puzzle in understanding geomagnetic storms and their impact on Earth's ionosphere. Major geomagnetic storms can put astronauts on the International Space Station and those on future interplanetary space missions in danger, damage satellites, cause failing radio communications, and harm electricity grids and pipelines and so have extensive and costly consequences for society. Studying and understanding geomagnetic storms are hence fundamental for global public and financial safety.
Magnetic fields from Sun and Earth connect
The known phenomenon of adding electrons to the ionosphere also occurs at high latitudes.
It happens because the sun's magnetic field, carried along with the stream of particles following a solar eruption, interferes with Earth's own magnetic field, fundamentally connecting with it. Particles, including electrons, in the solar outburst can penetrate the ionosphere, following Earth's magnetic field lines, which converge at the poles.
The explanation for this phenomenon lies presumably in the processes taking place in Earth's magnetic field in the direction away from the sun. Massive changes take place in the magnetic field composition in the area between the solar wind -- the stream of energetic particles flowing from the sun -- and Earth's magnetic field and this triggers powerful energy transfers.
"The forerunner of the phenomenon is a violent eruption on the sun's surface, called a coronal mass ejection, or CME, where the sun bubbles up, and slings 'hot' magnetized plasma in the form of very energetic ions and electrons in the direction of Earth," said Per Høeg.
The geomagnetic storm in the ionosphere over the Arctic in February 2014 was measured via satellites and from terrestrial stations. Among other sensors the GPS network GNET in Greenland provided a wealth of data.
Critical factors in satellite navigation
The research goes beyond the discovery of electrons being sucked out of the ionosphere during solar storms.
"There are two aspects of the research. First, it can be used for practical purposes;, also there is a theoretical part, which is about fundamentally better understanding these phenomena," said Tibor Durgonics who is a Ph.D. student at DTU Space and the main author of the new article in Radio Science.
"Our work can help to make navigation safer during geomagnetic storms in the Arctic. Through the new research, we have identified some critical factors affecting the quality of satellite navigation, and looked at the likelihood of when these factors may occur. On a more theoretical level, we found out, that these kind of storms can remove electrons from the ionosphere, which is the opposite of what one would expect intuitively."
When the magnetic field in solar eruptions impacts Earth's magnetic field in the ionosphere, their force fields get merged and, through a series of complex physical processes, ultimately cause unstable areas in the ionosphere called patches. These patches extend over large areas of 500 to 1000 km near the pole and also give rise to strong northern lights displays.
Interferes with navigation and communication systems
Knowledge of geomagnetic storms is important as communications via satellites and terrestrial radio channels can be impacted. The storms can disrupt the signals from GPS and other satellites and can cause widespread electricity outages, as for example happened in Sweden in 2003 and Canada in 1989.
"It is becoming increasingly important to be able to manage the impact of geomagnetic storms in that more and more of our infrastructure relies on radio signals for communications and navigation. Therefore, we are working to be able to describe and predict the geophysical changes at high latitudes, more accurately, so that among other things they can be taken into account in the design and operation of future communications systems," explains Per Høeg.
Per Høeg hopes that the work at DTU Space in addition to ensuring better understanding of the phenomenon can help in the development and operation of communications and navigation systems, and account for the conditions during geomagnetic storms so that aircraft and shipping can operate efficiently and safely in the area.
"We are seeing great interest in this field. Our latest results in particular have attracted attention from U.S. and Canadian research institutions," he said.
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