Chen and Wolf (1999) used a thin‐filament theory to construct a 2D model of a bursty bulk flow (BBF) motion inside the plasma sheet. The modeling revealed that the low‐entropy filament overshoots its equilibrium position and executes a heavily damped oscillation about that position. In this letter we demonstrate, for the first time, the multiple overshoot and rebound of a BBF observed by the five THEMIS probes on 17 March 2008 just after 10:22 UT. We found that the BBF oscillatory braking was accompanied by interlaced enhancements and depletions of radial pressure gradients. The earthward and tailward flow bursts caused formation of vortices with opposite sense of rotation.

[1] We study a substorm with two onsets (at 0220 and 0243 UT) that occurred during a gradual northward interplanetary magnetic field (IMF) turning on 16 February 2008. At these times, Time History of Events and Macroscale Interactions during Substorms (THEMIS) and GOES spacecraft were distributed between 6.6 and 18 R E downtail. Prior to the weak auroral electrojet onset at 0220 UT, a thin current sheet was extended near 10-11 R E . After the onset, Earthward fast flows with dipolarization fronts followed by signatures of magnetic flux pileup were detected in this region. The 0243 UT onset disturbances were more intense and centered at higher latitudes. The reconnection region tailward of 18 R E became activated and reached the lobe flux. We suggest that activations of reconnection Earthward of 18 R E associated with the 0220 UT event led to pileup of flux and redistribution of B Z to form a thin current sheet with small B Z in the midtail region. This made conditions favorable for reconnection tailward of 18 R E involving lobe flux for the 0243 UT onset. The reconfiguration process in the current sheet between the two onsets possibly enabled a relatively strong, high-latitude substorm despite the rather weak IMF driver. The near-Earth dipolarization observed after the 0243 UT onset was accompanied by more localized Earthward flows and flow reversals. Differences in dipolarization signatures could be caused by ambient plasma condition and field configuration between these two events. Our observations of the double-onset substorm suggest that the plasma sheet can be preconditioned by both the IMF driver and internal magnetotail processes.Citation: Nakamura, R., et al. (2011), Flux transport, dipolarization, and current sheet evolution during a double-onset substorm,

Flapping motion of the current sheets of planetary magnetotails is a common dynamic phenomenon. Previous studies of the Earth's magnetotail suggest that its flapping motion has two forms, that is, kink‐like flapping that can propagate as waves toward both flanks and steady flapping that moves up and down but does not propagate. Although some models have been proposed to explain the kink‐like flapping, its mechanism remains unclear. This paper surveys 87 flapping events statistically with respect to their flapping types, using the multipoint measurements of Cluster. The statistical results show that the up‐down steady flapping events tend to occur around the midnight region, and the kink‐like flapping events tend to occur near both flanks of the magnetotail. Thus, we propose that kink‐like flapping motion is causally related to steady flapping motion; that is, the up and down motion of steady flapping around the midnight region induces kink‐like flapping waves, which propagate toward both flanks of the magnetotail.

A kink‐like flapping event of Earth magnetotail current sheet, which consists of two frequency bands successively, is studied by the multipoint observations of Cluster. The multipoint analysis of Cluster observations demonstrates that the higher frequency band (period is about 10 min) has faster propagation velocity (about 30 km/s), shorter wavelength (about 3 RE), and smaller amplitude (1–1.5 RE). In contrast, the lower frequency band (period is about 22 min) shows slower propagation velocity (about 21 km/s), longer wavelength (about 4.4 RE), and larger amplitude (2–3 RE). Comparison with the flapping models demonstrates that the dispersion of theoretical models does not show consistency with the results of this event, which suggests that new or more advanced kink‐like flapping theories or models in the future have to consider the constraints of the dispersive properties demonstrated by this event.

Long-term simulations of energetic electron fluxes in many space plasma systems require accounting for two groups of processes with well separated time-scales: a microphysics of electron resonant scattering by electromagnetic waves and a macrophysics of electron adiabatic heating/transport by mesoscale plasma flows. Examples of such systems are Earth's radiation belts and Earth's bow shock, where ion-scale plasma injections and cross-shock electric fields determine a general electron energization, whereas electron scattering by waves relaxes anisotropy of electron distributions and produces small populations of high-energy electrons. The application of stochastic differential equations is a promising approach for including effects of resonant wave–particle interaction into codes tracing electrons in models of large-scale electromagnetic fields. This study proposes and verifies such equations for the system with non-diffusive wave–particle interactions, i.e., the system with nonlinear effects of phase trapping and bunching. We consider electron resonances with intense electrostatic whistler-mode waves often observed in the Earth's radiation belts. We demonstrate that nonlinear resonant effects can be described by stochastic differential equations with the non-Gaussian probability distribution of random variations of electron energies.

No abstract

No abstract

No abstract