Subscribe to our free daily newsletters
. 24/7 Space News .

Subscribe to our free daily newsletters

Cluster Discovers Internal Origin Of The Plasma Sheet Oscillations

illustration only
Paris (ESA) Jun 28, 2004
The plasma sheet oscillations have their source localized in the magnetotail centre and their excitation might be linked to the substorm process, according to a statistical study based on Cluster data. Published 06 March 2004, in Geophysical Research Letters, this study presents observational evidence not explained by any previous theoretical model and has triggered a burst of numerical modeling activity.

The flapping motions of the Earth’s plasma sheet are of internal origin, according to a large set of observations from the Cluster satellites. This dataset includes 58 rapid plasma sheet crossings, observed by Cluster near the magnetotail flanks.

Rapid large-amplitude magnetic variations are frequently observed in the centre of the magnetotail. These variations indicate up and down (north-south) oscillating current sheet motions, known as current sheet flapping motions.

Two possible origins of these motions have been proposed in the past: external (inhomogeneous solar wind) or internal (large–scale wave, emitted in the current sheet and/or propagating in the tail).

Before Cluster, no final conclusion could be drawn, due to the difficulties of separating spatial and temporal effects. This time, a systematic analysis of tens of rapid plasma sheet crossings suggests that the flapping motions are of internal origin.

Waves, called kink-like waves, are emitted in the centre of the tail and propagate toward the tail flanks. The properties of these waves (phase velocity, direction of propagation) differ from any local excitation mechanism, discussed so far in the literature. The FluxGate Magnetometer (PI: Prof. André Balogh) has been the primary experiment used for this data analysis.

"Previous studies […] suggested that substorms* play some role in the excitation of the flapping waves", reminds Prof. Victor Sergeev, lead author on this research, performed in close collaboration with the Space Research Institute /Austrian Academy of Sciences, Graz, and the Centre d'Etude Spatiale des Rayonnements (CNRS/Université Paul Sabatier), Toulouse, published 06 March 2004, in Geophysical Research Letters.

"This new finding not only supports this view, it also provides some constraints to the (yet) unknown mechanisms which destabilize the tail sheet in the substorm process and launch the kink waves", he added.

This new result is far from being the only one found by Cluster in the Earth’s magnetotail. In particular, Cluster has provided the first observational evidence of a very thin current sheet (few thermal ion gyroradii) [Nakamura et al., 2002], at times split into two layers, also called bifurcated current sheets [Runov et al., 2003]. In the latter case study, the two current sheets were also vertically flapping in the north-south direction.

"Finding bifurcated current sheets (BCSs) in the Earth’s magnetotail and the detailed description of their 3D spatial structure and flapping motions has become one of the most significant accomplishments of the unique four-spacecraft Cluster mission", underlined Dr. Mikhail Sitnov in a recent paper, published 8 May 2004 in Geophysical Research Letters.

Due to these new Cluster findings, this paper presents numerical simulation results, modeling the behaviour of the current sheet flapping motions. And there is more to come: "the new observations [performed by Cluster] triggered a burst of modeling activity", he added.

* Substorms: violent reconfigurations of the Earth's magnetic tail which, by change in the magnetic topology, convert magnetic energy to energize ions and electrons, inject some of them into the ring current, and greatly increase the rate at which energy is released in the magnetosphere.

Related Links
Search SpaceDaily
Subscribe To SpaceDaily Express

NCAR Instrument Gets Breakthrough View of Sun's Magnetic Halo
Boulder (SPX) Jun 02, 2004
A new instrument developed at the National Center for Atmospheric Research (NCAR) has captured landmark imagery of fast-evolving magnetic structures in the solar atmosphere. Steven Tomczyk (NCAR High Altitude Observatory) presented the images on Monday, May 31, at the annual meeting of the American Astronomical Society (AAS) in Denver.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.