Such colourful aurorae regularly light the higher latitudes in the northern and southern hemisphere. They are caused mostly by energetic electrons spiralling down the Earth's magnetic field lines and colliding with atmospheric atoms at about 100 kilometres altitude. These electrons come from the magnetotail, a region of space on the night-side of Earth where the Sun's wind of particles pushes the Earth’s magnetic field into a long tail.
At the tail's centre is a denser region known as the plasmasheet. Violent changes of the plasmasheet are known as magnetic substorms. They last up to a couple of hours and somehow hurl electrons and other charged particles earthwards. Apart from the beautiful light show, substorms also excite the Earth's ionosphere, perturbing the reception of GPS signals and communications between the Earth and orbiting satellites.
A key issue about substorms has been to determine how they fling material earthwards. The so called 'Bursty Bulk Flows' (BBFs), flows of gas that travel at over 300 kilometres per second through the plasmasheet, were discovered in the 1980s and became a candidate mechanism.
Observations suggested that BBFs were relatively small and typically lasted only 10 minutes, casting doubt on whether BBFs could play a major role in the magnetic substorm phenomenon. There was also doubt as to whether BBFs took place for all substorms.
Now these doubts are challenged by a statistical study of BBFs and magnetic substorms by Dr Jinbin Cao, Key Laboratory of Space Weather, CSSAR, Beijing, China, together with American and European colleagues.
Using observations of the central plasmasheet collected by three satellites of ESA's Cluster mission during July – October of 2001 and 2002, Cao and colleagues found 67 substorms and 209 BBFs. When they used the observations of only one spacecraft, they found that 78 percent of substorms are accompanied by at least one BBF. However, by combined observations from three out of the four Cluster spacecraft, they discovered that 95.5 percent of substorms are accompanied by BBFs. "For the first time, it seems possible that all substorms are accompanied by BBFs", says Cao.
Another key result of this work is that the average BBF duration is longer than previously estimated. Single satellite observations confirmed past results that the BBF duration was around 10 minutes.
However, by combining the data from three of the Cluster spacecraft, the observations reveal an average duration almost twice as long: 18 minutes and 25 seconds. So again, the multiple spacecraft data offered by Cluster was found to reveal more about the Earth's magnetic environment than data collected by single spacecraft.
"These new results by the Cluster mission clearly show that multi-point observations are the key to understanding the magnetic substorm phenomenon," says Philippe Escoubet, Cluster and Double Star Project Scientist of the European Space Agency.
Philippe Escoubet | alfa
Physicists discover that lithium oxide on tokamak walls can improve plasma performance
22.05.2017 | DOE/Princeton Plasma Physics Laboratory
Experts explain origins of topographic relief on Earth, Mars and Titan
22.05.2017 | City College of New York
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
Dental plaque and the viscous brown slime in drainpipes are two familiar examples of bacterial biofilms. Removing such bacterial depositions from surfaces is...
For the first time, scientists have succeeded in studying the strength of hydrogen bonds in a single molecule using an atomic force microscope. Researchers from the University of Basel’s Swiss Nanoscience Institute network have reported the results in the journal Science Advances.
Hydrogen is the most common element in the universe and is an integral part of almost all organic compounds. Molecules and sections of macromolecules are...
22.05.2017 | Event News
17.05.2017 | Event News
16.05.2017 | Event News
22.05.2017 | Materials Sciences
22.05.2017 | Life Sciences
22.05.2017 | Physics and Astronomy