From ESA: “Swarm detects asymmetry”

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European Space Agency

22 March 2017

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Title Swarm
Released 23/03/2012 1:18 pm
Copyright ESA/AOES Medialab
Swarm is ESA’s first constellation of Earth observation satellites designed to measure the magnetic signals from Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere, providing data that will allow scientists to study the complexities of our protective magnetic field.

Strong electric currents in the upper atmosphere are known to vary according to the season, but ESA’s Swarm mission has discovered that this seasonal variation is not the same in the north and south polar regions.

Named after Kristian Birkeland, the scientist a century ago who first postulated that the ‘northern lights’ were linked to electrically charged particles in the solar wind, these currents flow along Earth’s magnetic field lines in the polar regions.

Magnetic field measurements from ESA’s Swarm satellite constellation are allowing scientists to understand more about these powerful currents, which carry up to 1 TW of electric power to the upper atmosphere. This is about 30 times the energy consumed in New York during a heatwave.

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Title Seasonal asymmetry
Released 22/03/2017 10:24 am
Copyright DTU/BCSS
Three years of measurements from ESA’s Swarm mission have be combined with measurements from Germany’s earlier Champ satellite to produce global climatological maps of Birkeland currents. These currents tend to be weak for a northwards interplanetary field and strong for a southwards field. Importantly, these new results also reveal that the strength of the currents is not the same in both hemispheres. These hemispheric differences may relate to asymmetry in Earth’s main magnetic field.

It is important to understand the interplay between these Birkeland currents and the solar wind that bombards our planet and that can potentially cause power and communication blackouts.

New findings, presented this week at the Swarm science meeting in Canada, show how three years of measurements from the mission were combined with measurements from Germany’s earlier Champ satellite to produce global climatological maps of these currents.

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Title Earth’s protective shield
Released 06/02/2014 2:09 pm
Copyright ESA/ATG medialab
The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds.

Moreover, these results show differences between currents in the northern and southern hemisphere, how they change with the season and how they vary according to the strength of the solar wind.

Karl Laundal, from the Birkeland Centre for Space Science, explained, “Interaction between Earth’s magnetic field and the interplanetary magnetic field – meaning part of the Sun’s magnetic field carried by solar wind – depends on how the interplanetary field is orientated.

“While this sounds complicated, it means that hardly any solar wind can enter the magnetosphere and arrive at Earth if the interplanetary magnetic field points north, parallel to Earth’s magnetic field.

“On the other hand, if the interplanetary field points south, the opposite is true and this allows a connection to be made with Earth’s magnetic field.

“Part of the energy in solar wind then further energises the charged particles that are responsible for the visible light displays of the auroras.”

Birkeland currents therefore tend to be weak for a northwards interplanetary field and strong for a southwards field.

Importantly, these new results also reveal that the strength of the currents is not the same in both hemispheres. These hemispheric differences may relate to asymmetry in Earth’s main magnetic field.

In fact, the two geomagnetic poles are not geometrically opposite to one another, and the magnetic field intensity is also not the same in the north as in the south.

Dr Laundal said, “The main reason for this probably has to do with differences in Earth’s main field. Such differences imply that the ionosphere–magnetosphere coupling is different in the two hemispheres.

“In particular, the magnetic pole is more offset with respect to the geographic pole in the south compared to north, which leads to different variations in sunlight in the ‘magnetic hemispheres’. Because of these differences, the two hemispheres do not respond symmetrically to solar wind driving or changing seasons.

“Swarm is a fantastic tool for space science studies. The high-quality measurements and the fact that there are three satellites working in concert hold many new clues about how our home planet interacts with the space around it. It’s a fascinating time.”

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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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