Outstanding Swedish research results from the Cluster satellites in the Earth’s magnetosphere

Scientists from the Swedish Institute of Space Physics (IRF) in Uppsala have published two articles in the September issue of Physical Review Letters , a leading journal for short communications in physics. Both articles are based on data from instruments on board the Cluster satellites. The four satellites were launched in 2000 and are orbiting the Earth in formation to study phenomena in the magnetosphere, the protective magnetic field round our planet. The new results deal with (1) magnetic reconnection – a long-debated process whereby magnetic field energy is converted into particle energy, and (2) a theory of large amplitude nonlinear structures in collisonless plasma that has been verified with measurements from Cluster.

The two articles are described below:

“Structure of the Magnetic Reconnection Diffusion Region from Four-Spacecraft Observations” by A. Vaivads, Y. Khotyaintsev, M. Andre, A. Retino, S.C. Buchert (all at IRF in Uppsala), B. Rogers, P. Decreau, G. Paschmann, T. Phan.

Magnetic reconnection is a physical process that in astrophysical plasma environements allows an efficient conversion of magnetic field energy into the energy of ions and electrons. While energy conversion takes place in a large volume, the reconnection is initiated in small regions, so-called diffusion regions. So far the best experimental observations of the reconnection are from the Earth’s magnetosphere. The Cluster mission has for the first time allowed observation of the diffusion regions using multi-spacecraft data. This paper presents the first such observations and shows that the diffusion region is dominated by the Hall physics, that reconnection rate is fast and that there are strong parallel currents across the edges (separatrices) of the diffusion region. The results are of importance to space, astrophysical and laboratory plasma environments.

The article is available online from the American Physical Society:
http://link.aps.org/abstract/PRL/v93/e105001

“Theory and Observations of Slow-mode Solitons in Space Plasmas” by K. Stasiewicz (Swedish Institute of Space Physics in Uppsala)

When the supersonic solar wind flow is retarded at the collisonless bow shock in front of the magnetosphere, large numbers of nonlinear plasma structures are formed downstream in the magnetosheath: solitons, magnetic holes and mirror-mode waves. The nonlinearity of these structures expressed as dB/B may reach 200% or even more. This paper provides a quantitative model of these structures, a model which explains amplitudes, spatial scales, polarization, propagation properties and parameter space for their occurrence. The model is verified with the multipoint measurements obtained with the ESA/NASA Cluster mission and may be of general interest for other disciplines where strong turbulence and transition between chaos and structure formation are significant.

The article is available online from the American Physical Society:
http://link.aps.org/abstract/PRL/v93/e125004

**More information:
** Rick McGregor, Information Officer, IRF, tel. +46-980-79178, rick.mcgregor@irf.se