Articles | Volume 25, issue 1
01 Feb 2007
 | 01 Feb 2007

Ion multi-nose structures observed by Cluster in the inner Magnetosphere

C. Vallat, N. Ganushkina, I. Dandouras, C. P. Escoubet, M. G. G. T. Taylor, H. Laakso, A. Masson, J.-A. Sauvaud, H. Rème, and P. Daly

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.