Generally seen in high-latitude regions such as Scandinavia or Canada, aurorae are colourful curtains of light that appear in the sky. Caused by the interaction of high-energy particles brought by the solar wind, with Earth’s magnetic field, they appear in many different shapes.
These substorms typically last one to two hours and are three-dimensional physical phenomena spread over altitudes from 100 to 150 000 kilometres. Trying to understand such complex physical processes with a single scientific spacecraft is like trying to predict the behaviour of a tsunami with a single buoy in an ocean. That is why, the simultaneous use of several satellites like the Cluster constellation is necessary to understand these events.
Currently, there are two competing theoretical models to describe these substorms or space tsunamis. The first one is called the ‘Current-Disruption’ model, while the second one is the ‘Near Earth Neutral Line Model’. Using data from the four Cluster spacecraft, a group of scientists from both sides of the Atlantic were able to confirm that the behaviour of some substorms is consistent with the Current Disruption model.
A substorm develops and builds up in different stages, and it is the detailed study of one of these stages that helps us to understand which of the two models apply. For example, in the late stage of substorm development, auroral disturbances move towards the poles, suggesting that the energy source for auroras and substorms moves away from Earth.
Previous satellite observations have found that, during this late stage, the flows of plasma (a gas of charged particles populating Earth’s magnetosphere) in the magnetotail exhibit a reversal in direction. In recent years it was generally thought that a flow reversal region is where magnetic reconnection takes place, that is where the energy of the magnetic field is converted into particle energy (dissipation effect), resulting in high-speed plasma flows that hurl towards Earth, like space tsunamis.
Detailed analysis of data obtained by the Cluster satellites while crossing such a region in the magnetotail, where flows of plasma exhibit a reversal in direction, has been reported by the team of Dr Tony Lui, a scientist of the Applied Physics Laboratory at the John Hopkins University, Maryland, USA, Co-Investigator of the Research with Adaptive Particle Imaging Detectors (RAPID) high-energy particles experiment on Cluster, and lead author of the study. Thanks to the unique capability of Cluster to perform simultaneous multipoint measurements, the scientists were able to derive several physical parameters never before estimated for such a flow reversal region.
By comparing the directions of the electric current and the electric field in the magnetosphere it is possible to understand whether the cause of the flow reversal is a dissipation effect (where magnetic field energy converted to particle energy) or a dynamo effect (where particle energy is converted to magnetic field energy). For this case study, the Cluster scientists observed that features associated with flow reversal are actually very complex, consisting of both dissipation and dynamo effects in localised sites.
This result shows that the plasma turbulence disrupts the local electric current. “The features we observed are consistent with the current disruption model. However, it is unclear how general these findings are. More events will be examined in the future," said Dr Lui.
"The magnetic substorm phenomenon is a hot topic of research,” added Philippe Escoubet, Cluster and Double Star project scientist for ESA. “This new Cluster result will certainly contribute to the on-going scientific debate and foster research cooperation with scientists involved in the newly launched NASA Time History of Events and Macroscale Interactions during Substorms (THEMIS), a mission specifically dedicated to studying substorms.”
Philippe Escoubet | alfa
Wandering greenhouse gas
16.03.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Unique Insights into the Antarctic Ice Shelf System
14.03.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...
On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...
The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...
At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.
When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...
At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.
Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...
16.03.2018 | Event News
13.03.2018 | Event News
08.03.2018 | Event News
16.03.2018 | Earth Sciences
16.03.2018 | Physics and Astronomy
16.03.2018 | Life Sciences