Artist's impression of the oscillations of the magnetic field lines (www.futura-sciences.com)
Science Nuggets: Magnetospheric physics
Determining the shape and the motion of the plasmapause
Non-thermal continuum radiation (NTC) is electromagnetic waves generated in plasma density gradients and that is present at all magnetised planets. Terrestrial NTC is widely believed to be generated in the equatorial region of the boundary that separates the dense inner magnetosphere and less dense magnetotail known as the plasmapause. The region in which the NTC is generated is very small, making it almost impossible to directly observe due to limitations in spacecraft and their instrumentation. However, the study of the NTC frequency allows us to determine the shape and the motion of the plasmapause in this source region.
Oscillations observed on the NTC bands at the perigee pass with Cluster 4 WHISPER's spectrogram. Image adapted from Grimald et al. (2009)
In a recent paper, Grimald et al. (2009) presented an NTC event in which the spectral signature showed oscillating bands. The magnetic field data from the same interval showed that the NTC oscillations were correlated with oscillations in the magnetic field data. By locating the NTC source position, studying the NTC source motion and the period of oscillations observed in the NTC bands and in the magnetic field lines, they showed the two phenomenon are linked. This allowed Grimald et al. to determine the propagation mode of the wave responsible of the oscillations of the magnetic field lines and to determine the shape of the plasmapause in the NTC source region.
For more details, see:
S. Grimald, C. Foullon, P. M. E. Décréau, G. Le Rouzic, X. Suraud, X. Vallières
Modulation of NTC frequencies by Pc5 ULF pulsations: experimental test of the generation mechanism and magnetoseismology of the emitting surface
J. Geophys. Res., in press (2009), [Online]