Abstract
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.
Highlights
During the last 30 years, several inner magnetospheric missions have recorded the presence of various fine structures in the proton spectrograms, which have been referred as “noselike” structures due to the shape of the created features in the energy-time spectrograms
In this paper we present a study of the narrow energy structures observed in the ion spectrograms at medium energies by Cluster/CODIF at 4 RE, and their main characteristics were deduced from a statistical study (163 perigee passes of Cluster)
– The detailed analysis of CODIF spectrograms during Cluster perigee pass revealed that several different types of structures are observed at 4 RE by CODIF
Summary
During the last 30 years, several inner magnetospheric missions have recorded the presence of various fine structures in the proton spectrograms, which have been referred as “noselike” structures due to the shape of the created features in the energy-time spectrograms These features are characterized by a deeper inward penetration of particles coming from the tail at a given energy. Using the same data, Ejiri et al (1980) described the phenomenon responsible for these structures as a two steps process: first plasma issued from the plasma sheet is injected inward by a relatively weak convective electric field This field increases suddenly, leading to an energy dispersion of the ions. These nose-like structures were referred as “substorm nose structures”. Ejiri et al (1980) observed that a minimum AE threshold of 250 nT was necessary to observe substorm nose structures at these distances
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