HR: 0800h
AN: SM41A-1167    [Abstracts]
TI: Study of structures observed in the CODIF-Cluster ion spectrograms during Cluster perigee passes
AU: * Vallat, C
EM: vallat@cesr.fr
AF: CESR/CNRS, 9 avenue du colonel Roche BP 4346, Toulouse, 31028 France
AU: Ganushkina, N
EM: Nataly.Ganushkina@fmi.fi
AF: FMI, Erik Palm‚nin aukio, HELSINKI, 00560 Finland
AU: Dandouras, I
EM: dandouras@cesr.fr
AF: CESR/CNRS, 9 avenue du colonel Roche BP 4346, Toulouse, 31028 France
AB: During the last 30 years, several magnetospheric missions have recorded the presence of narrow structures in the proton spectrograms in the ring current region. These structures have been referred as `nose-like' structures, due to the shape these structures were forming on the time energy spectrograms, characterized by a flux value increase for a narrow energy range. For energies above 10 keV, these structures have been interpreted as the result of substorm associated convection, together with adiabatic motion of particles in a stationary electric and magnetic fields. This structure has been referred as `substorm nose structure'. Another type of nose has also been observed during quiet periods at lower energy ranges. This latter type is formed by two simultaneous gaps, at lower and higher energy, and has been named `stationary nose structure'. Cluster's highly eccentric polar orbit at 4 Re perigee permits the sampling of the ring current region. The ion distribution functions obtained in situ by the CIS experiment (for energies of about 5eV/q to 40 keV/q) reveal, for the first time, the simultaneous presence of several narrow nose-like structures for all MLT sectors. 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, characteristic energy of the nose reveals a clear MLT dependence: a sharp transition in the energy range occurs in the noon sector for quiet events (Kpœ1) and in the morning sector for more disturbed events (Kp>1). Moreover, these multi-nose structures (up to 3 simultaneous noses) appear regardless of the magnetospheric activity level and/or the MLT sector crossed by the spacecraft. This work presents a statistical distribution of these `nose-like' structures and their main characteristics, using one year and a half of Cluster-CIS data. Numerical simulations of particles trajectories, using large-scale electric and magnetic field models, will also be presented. These are essential to understand which are the main magnetospheric parameters responsible for the formation of such structures.
DE: 2730 Magnetosphere: inner
DE: 2764 Plasma sheet
DE: 2778 Ring current
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005