From ESA: “Swarm details energetic coupling”

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European Space Agency

15 February 2018

ESA/Swarm

The Sun bathes our planet in the light and heat it needs to sustain life, but it also bombards us with dangerous charged particles in solar wind. Our magnetic field largely shields from this onslaught, but like many a relationship, it’s somewhat complicated. Thanks to ESA’s Swarm mission the nature of this Earth–Sun coupling has been revealed in more detail than ever before.

Earth’s magnetic field is like a huge bubble, protecting us from cosmic radiation and charged particles carried by powerful winds that escape the Sun’s gravitational pull and sweep across the Solar System.

Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

The trio of Swarm satellites were launched in 2013 to improve our understanding of how the field is generated and how it protects us from this barrage of charged particles.

Since our magnetic field is generated mainly by an ocean of liquid iron that makes up the planet’s outer core, it resembles a bar magnet with field lines emerging from near the poles.

The field is highly conductive and carries charged particles that flow along these field lines, giving rise to field-aligned currents.

Carrying up to 1 TW of electrical power – about six times the amount of energy produced every year by wind turbines in Europe – these currents are the dominant form of energy transfer between the magnetosphere and ionosphere.

The shimmering green and purple light displays of the auroras in the skies above the polar regions are a visible manifestation of energy and particles travelling along magnetic field lines.

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Aurora borealis
Released 21/04/2017
Copyright Sherwin Calaluan
The aurora borealis is a visible display of electrically charged atomic particles from the Sun interacting with Earth’s magnetic field.

The theory about the exchange and momentum between solar wind and our magnetic field actually goes back more than 100 years, and more recently the Active Magnetosphere and Planetary Electrodynamics Response Experiment satellite network has allowed scientists to study large-scale field-aligned currents.

However, the Swarm mission is leading to exciting new wave of discoveries. A new paper [Journal of Geophysical Research] explores the dynamics of this energetic coupling across different spatial scales – and finds that it’s all in the detail.

Ryan McGranaghan from NASA’s Jet Propulsion Laboratory said, “We have a good understanding of how these currents exchange energy between the ionosphere and the magnetosphere at large scales so we assumed that smaller-scale currents behaved in the same way, but carried proportionally less energy.”

“Swarm has allowed us to effectively zoom in on these smaller currents and we see that, under certain conditions, this is not the case.

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Solar corona viewed by Proba-2
Released 16/03/2015
Copyright ESA/ROB
This snapshot of our constantly changing Sun catches looping filaments and energetic eruptions on their outward journey from our star’s turbulent surface.

The disc of our star is a rippling mass of bright, hot active areas, interspersed with dark, cool snaking filaments that wrap around the star. Surrounding the tumultuous solar surface is the chaotic corona, a rarified atmosphere of super-heated plasma that blankets the Sun and extends out into space for millions of kilometres.

This coronal plasma reaches temperatures of several million degrees in some regions – significantly hotter than the surface of the Sun, which reaches comparatively paltry temperatures of around 6000ºC – and glows in ultraviolet and extreme-ultraviolet light owing to its extremely high temperature. By picking one particular wavelength, ESA’s Proba-2 SWAP (Sun Watcher with APS detector and Image Processing) camera is able to single out structures with temperatures of around a million degrees.

ESA Proba 2

As seen in the above image, taken on 25 July 2014, the hot plasma forms large loops and fan-shaped structures, both of which are kept in check by the Sun’s intense magnetic field. While some of these loops stay close to the surface of the Sun, some can stretch far out into space, eventually being swept up into the solar wind – an outpouring of energetic particles that constantly streams out into the Solar System and flows past the planets, including Earth.

Even loops that initially appear to be quite docile can become tightly wrapped and tangled over time, storing energy until they eventually snap and throw off intense flares and eruptions known as coronal mass ejections. These eruptions, made up of massive amounts of gas embedded in magnetic field lines, can be dangerous to satellites, interfere with communication equipment and damage vital infrastructure on Earth.

Despite the Sun being the most important star in our sky, much is still unknown about its behaviour. Studying its corona in detail could help us to understand the internal workings of the Sun, the erratic motions of its outer layers, and the highly energetic bursts of material that it throws off into space.

Two new ESA missions will soon contribute to this field of study: Solar Orbiter is designed to study the solar wind and region of space dominated by the Sun and also to closely observe the star’s polar regions, and the Proba-3 mission will study the Sun’s faint corona closer to the solar rim than has ever before been achieved.

NASA/ESA Solar Orbiter

ESA Proba 3

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“Our findings show that these smaller currents carry significant energy and that their relationship with the larger currents is very complex. Moreover, large and small currents affect the magnetosphere–ionosphere differently.”

Colin Forsyth from University College London noted, “Since electric currents around Earth can interfere with navigation and telecommunication systems, this is an important discovery.

“It also gives us a greater understanding of how the Sun and Earth are linked and how this coupling can ultimately add energy to our atmosphere.

“This new knowledge can be used to improve models so that we can better understand, and therefore, ultimately, prepare for the potential consequences of solar storms.”

ESA’s Swarm mission manager, Rune Floberghagen, added, “Since the beginning of the mission we have carried out projects to address the energy exchange between the magnetosphere, ionosphere and the thermosphere.

“But what we are witnessing now is nothing short of a complete overhaul of the understanding of how Earth responds to and interacts with output from the Sun.

“In fact, this scientific investigation is becoming a fundamental pillar for the extended Swarm mission, precisely because it is breaking new ground and at the same time has strong societal relevance. We now wish to explore this potential of Swarm to the fullest.”

See the full article here .

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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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