|
|
 |
|
|
Ann. Geophys., 25, 171-190, 2007
www.ann-geophys.net/25/171/2007/
© European Geosciences Union 2007
Ion multi-nose structures observed by Cluster in the inner Magnetosphere
C. Vallat1,3, N. Ganushkina2, I. Dandouras3, C. P. Escoubet1, M. G. G. T. Taylor1, H. Laakso1, A. Masson1, J.-A. Sauvaud3, H. Rème3, and P. Daly4
1ESTEC, European Space Agency, 2201 AZ Noordwijk, The Netherlands
2Finnish Meteorological Institute, 11010 Helsinki, Finland
3Centre d'Etude Spatiale des Rayonnements, Systeme Solaire, Toulouse, France
4Max Planck Institue for Solar System Research, Katlenburg-Lindau, Germany
Abstract. During the last 30 years, several magnetospheric missions have recorded the
presence of narrow proton structures in the ring current region. These
structures have been referred as "nose-like" structures, due to their
appearance when represented in energy-time spectrograms, characterized by a
flux value increase for a narrow energy range.
Cluster's polar orbit, with a 4 RE perigee, samples the ring current
region. The ion distribution functions obtained in-situ by the CIS
experiment (for energies of ~5 eV/q to 40 keV/q) reveal the
simultaneous presence of several (up to 3) narrow nose-like structures. A
statistical study (over one year and a half of CIS data) reveals that double
nose structures are preferentially observed in the post-midnight sector.
Also, the characteristic energy of the nose (the one observed at the lower
energy range when several noses occur simultaneously) reveals a clear MLT
dependence during quiet events (Kp<2): a sharp transition in the energy
range occurs in the pre-noon sector. Moreover, the multi-nose structures (up
to 3 simultaneous noses) appear regardless of the magnetospheric activity
level and/or the MLT sector crossed by the spacecraft.
Numerical simulations of particles trajectories, using large-scale electric
and magnetic field models are also presented. Most of the features have been
accurately reproduced (namely the single and double noses), but the triple
noses cannot be produced under these conditions and require to consider a
more complex electric field model.
Full Article in PDF (2581 KB) |
|
|
