Formation of intense nose structures

Ganushkina, N. Y.; Pulkkinen, Tuija; Bashkirov, Vladimir F.; Baker, D. N.; Li, Xinlin

doi:10.1029/2000gl011955

Cited by 59 publications

(72 citation statements)

References 11 publications

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“…Ganushkina et al (2000Ganushkina et al ( , 2001) studied the penetration of the plasma sheet ions into the inner magnetosphere using the Li et al (1998) model, together with stationary electric and magnetic fields for particle tracing. They concluded that the inward displacement of these intense nose structures can occur under short-lived impulsive electric fields, combined with the convection electric field.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Role of substorm-associated impulsive electric fields in the ring current development during storms

2005

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Abstract.Particles with different energies produce varying contributions to the total ring current energy density as the storm progresses. Ring current energy densities and total ring current energies were obtained using particle data from the Polar CAMMICE/MICS instrument during several storms observed during the years 1996-1998. Four different energy ranges for particles are considered: total (1-200 keV), low (1-20 keV), medium (20-80 keV) and high (80-200 keV). Evolution of contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases is followed. To model this evolution we trace protons with arbitrary pitch angles numerically in the drift approximation. Tracing is performed in the large-scale and small-scale stationary and time-dependent magnetic and electric field models. Small-scale time-dependent electric field is given by a Gaussian electric field pulse with an azimuthal field component propagating inward with a velocity dependent on radial distance. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during storm events. We demonstrate that such fluctuating fields in the form of localized electromagnetic pulses can effectively energize the plasma sheet particles to higher energies (>80 keV) and transport them inward to closed drift shells. The contribution from these high energy particles dominates the total ring current energy during storm recovery phase. We analyse the model contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases. By comparing these results with observations we show that the formation of the ring current is a combination of large-scale convection and pulsed inward shift and consequent energization of the ring current particles.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Role of substorm-associated impulsive electric fields in the ring current development during storms

2005

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“…They only considered as nose the structures presenting flux values above 10 6 (cm 2 s sr keV) −1 , whereas CODIF reveals nose structures with smaller fluxes. As a consequence, and if we assume that the absolute flux values increase with increasing activity, it is not surprising that the number of intense events increases with increasing K p , and that the flux threshold defined by Ganushkina et al (2001) is more often reached during more active periods.…”

Section: Statisticsmentioning

confidence: 99%

“…Ganushkina et al (2001) demonstrated that large-scale electric field changes are not sufficient to explain the fast formation (less than one hour) of these "intense nose events", as named by the authors. They showed that local pulses in the electric field (up to 4 mV/m) associated with substorm dipolarization are necessary to explain such rapid formation time and radial location of the observed features.…”

Section: Introductionmentioning

confidence: 99%

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

Vallat

Ganushkina

Dandouras³

et al. 2007

Ann. Geophys.

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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 R E 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 (K p <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.

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“…Birn (1987) traced particles in three-dimensional MHD simulations of dipolarization in the magnetotail and showed that particles are mainly accelerated by the betatron mechanism as they are transported by a time-dependent dawn-dusk electric field from the region of a weak magnetic field downtail to a stronger magnetic field at a geosynchronous orbit. Other simulations used an azimuthally wide earthward-propagating electromagnetic pulse to explain geosynchronous injections (e.g., Zaharia et al, 2000;Ganushkina et al, 2001Ganushkina et al, , 2005Ganushkina et al, , 2013Sarris et al, 2002;Li et al, 2003). Authors concluded that injections can be caused by the earthward compression magnetic field perturbation and its associated electric field corresponding to a global magnetotail dipolarization.…”

Section: Introductionmentioning

confidence: 99%

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

et al. 2018

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Abstract. The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X ∼ −7-−9 R E ) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the B Z magnetic field lasted ∼ 13 min and it was comprised of several B Z pulses or dipolarization fronts (DFs) with duration ≤ 1 min. Multipoint observations have shown that the beginning of the increase in suprathermal (> 50 keV) electron fluxes -the injection boundary -was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the B Z field, and it was comprised of multiple short (∼ few minutes) electron injections associated with the B Z pulses. This behavior can be explained by the combined action of local betatron acceleration at the B Z pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization.On the contrary, proton injections were detected only in the vicinity of the strongest B Z pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a finite energy range ∼ 70-90 keV. This feature can be explained by the nonadiabatic resonant acceleration of protons by the bursts of the dawn-dusk electric field associated with the B Z pulses.

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Formation of intense nose structures

Cited by 59 publications

References 11 publications

Role of substorm-associated impulsive electric fields in the ring current development during storms

Role of substorm-associated impulsive electric fields in the ring current development during storms

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

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

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