Multiple discrete-energy ion features in the inner magnetosphere: 9 February 1998, event

Abstract

Abstract. Multiple discrete-energy ion bands observed by the Polar satellite in the inner magnetosphere on 9 February 1998 were investigated by means of particle simulation with a realistic model of the convection electric field. The multiple bands appeared in the energy vs. L spectrum in the 1-100 keV range when Polar traveled in the heart of the ring current along the outbound and inbound paths. We performed particle tracing, and simulated the energy vs. L spectra of proton fluxes under the dipole magnetic field, the corotation electric field, and the realistic convection electric field model with its parameters depending on the solar wind data. Simulated spectra are shown to agree well with the observed ones. A better agreement is achieved when we rotate the convection electric potential eastward by 2 h in MLT and we change the distribution function in time in the nearEarth magnetotail. It is concluded that the multiple bands are likely produced by two processes for this particular event, that is, changes in the convection electric field (for >3 keV protons) and changes in the distribution function in the nearEarth magnetotail (for <3 keV protons).

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

“…However, this interpretation is unlikely to explain the bands observed by CODIF on the 11 April 2002, since no dipolarization signature is observed during the 8 h prior to the event (AE index very low). Using a realistic electric and magnetic field model (with solar wind data as input), Ebihara et al (2004) simulated the same event as Li et al (2000). They were thus able to conclude that these bands were most likely to be produced by two combined process, i.e.…”

“…However, using a realistic large scale electric field model, our simulations couldn't reproduce the bands observed by CODIF during the 11 April 2002 event. As a consequence, the interpretation made by Ebihara et al (2004) is unlikely to explain CODIF structures in that case. Moreover, using real LANL/MPA data as input in our model, no change in the source distribution function was able to explain the creation of low energy structures.…”

“…First, variations in the azimuthal location of the source: the drift path of particles from the source to the evening sector would be longer, leading to the creation of a gap, and hence split nose in that sector. They could also be due to a change of the global electric field, affecting the nose energy, and leading to the appearance of a nose at different energy, coexisting locally with the one previous to the change (Ebihara et al, 2004). Finally, a modification of the ionospheric conductivity could also lead to a new distribution of the current closure, thus affecting the resulting electric field (Fok et al, 2001).…”

“…decrease in the number density) in the near Earth magnetotail (for <3 keV protons). According to Ebihara et al (2004), a change in the electric field leads to the drift of the stagnation point (i.e. where the sum of the ion drift velocities is zero), and a satellite placed on the closed orbit will detect the gap periodically.…”

“…Particles are injected deeply inward, following the electric field increase, and they start to disperse, high energy particles drifting faster around the Earth than low energy ones, their population superposing the slower one locally. On the other hand, Ebihara et al (2004) interpreted this feature as the result of two combined processes: a change in the convection electric field together with a change in the distribution function of the source to explain the low energy particles features. They showed that a change in the convection electric field can move the nose energy range to higher or lower energies, leading to the simultaneous observation of the "old" nose (created before the convection electric field change) together with a new one.…”