Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cluster – new insights into the electric circuits of polar lights

12.02.2007
Giant electrical circuits power the magical open-air light show of the auroras, forming arcs in high-latitude regions like Scandinavia. New results obtained thanks to ESA's Cluster satellites provide a new insight into the source of the difference between the two types of electrical circuits currently known to be associated to the auroral arcs.

The deep mechanisms that rule the creation of the beautiful auroras, or polar lights, have been the subject of studies that have kept solar and plasma scientists busy for many years. While early rockets and ground-observations have already provided a few important clues for the understanding of these phenomena, the real breakthroughs in our knowledge have started with dedicated auroral satellites, such as S3-3, Dynamics Explorer, Viking, Freja and FAST, and have now come to full fruition with ESA's multi-point mission Cluster.

The basic process generating auroras is similar to what happens in an old TV tube. In the TV tube, accelerated electrons hit the screen and make its phosphore glow; electrons in the atmosphere get accelerated in an 'acceleration region' situated between about 5000 and 8000 kilometres altitude, and rush down to the Earth's ionosphere – a region of the upper atmosphere. Here, they crash into ionospheric atoms and molecules, transfer to them some of their energy and so cause them to glow, creating aurorae.

It is today well established that almost-static electric fields, parallel to the Earth's magnetic fields, play an important role in the acceleration of the electrons that cause the auroras to shine. The auroral electric circuits in the near-Earth space involve almost-static 'electric potential' structures through which electrons and ions are accelerated in opposite directions - towards and away from Earth's atmosphere -at high latitudes.

It had been observed that these electric potential structures are mainly of two types - symmetric (U-shaped) or asymmetric (S-shaped). In 2004, Prof. Göran Marklund from the Alfvén Laboratory, at the Royal Institute of Technology, Stockholm (Sweden), noted that the U-shaped and the S-shaped structures typically occurred at the boundaries between magnetospheric regions with different properties.

The former type (U-shaped) was found at a plasma boundary between the so-called ‘central plasma sheet’, situated in the magnetotail at equatorial latitudes, and the ‘plasma sheet boundary layer’, an adjacent area located at higher latitudes. The latter type (S-shaped) was found at the boundary between the ‘plasma sheet boundary layer’ and the polar cap, further up in latitude.

Marklund was then in the condition to propose a model to explain this difference. The model suggested that both the asymmetric and symmetric shape of the potential structures, observed at the different plasma boundaries, depended on the specific conditions of the plasma (such as differences in plasma density) in the two regions surrounding the boundary. According to the 2001 observations, he concluded that the plasma conditions at the lower-latitude boundary (where U-shaped structures were observed) are in general more symmetric, while the ones at the polar cap boundary (where the S-shaped structures were observed) are more asymmetric.

However, new Cluster measurements did not seem to be consistent with this picture. On 1 May 2003, one of the Cluster spacecraft crossed the auroral arc at high altitude in the Earth’s magnetotail. As expected, it detected the presence of a U-shaped, symmetric potential structure when crossing the boundary between the 'central plasma sheet' and the 'plasma sheet boundary layer'. Only 16 minutes later a second Cluster spacecraft, moving roughly along the same orbit and crossing the same boundary, detected an asymmetric, S-shaped potential structure, 'typical' of the polar cap boundary and therefore unexpected in that region.

However, within the 16-minute time frame between the crossing of the two spacecraft, the plasma density and the associated currents and fluxes of particles decreased significantly in the plasma sheet boundary layer. In this way this boundary ended up in resmbling the asymmetric conditions typical of the polar cap boundary.

So, the scientists interpreted that the 'reconfiguration' from a U-shaped to a S-shaped potential structure, and of the associated electric circuits that sustain the auroral arcs, reveal the change in the plasma conditions on the two sides of the boundary.

The results represent a major step forward in understanding the auroral electrical circuits, but important questions still remain open, such as: how do the process that accelerate the electrons to form auroras get triggered and maintained? Cluster measurements in the 'acceleration' area to be performed in 2008 and 2009 should help us to find out.

Philippe Escoubet | alfa
Further information:
http://www.esa.int/esaSC/SEM0EZN2UXE_index_0.html

More articles from Earth Sciences:

nachricht A promising target in the quest for a 1-million-year-old Antarctic ice core
24.05.2018 | University of Washington

nachricht Tropical Peat Swamps: Restoration of Endangered Carbon Reservoirs
24.05.2018 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Powerful IT security for the car of the future – research alliance develops new approaches

The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.

Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...

Im Focus: Molecular switch will facilitate the development of pioneering electro-optical devices

A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.

The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...

Im Focus: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

In focus: Climate adapted plants

25.05.2018 | Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

 
Latest News

In focus: Climate adapted plants

25.05.2018 | Event News

Flow probes from the 3D printer

25.05.2018 | Machine Engineering

Less is more? Gene switch for healthy aging found

25.05.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>