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Zelenyi, Lev M.

Publications and source records attributed to Zelenyi, Lev M..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

The Influence of Convection on Magnetotail Variability

This study investigates the evolution of the magnetotail's magnetic field with the aid of a self-consistent two-dimensional model. In this model the plasma mantle continuously supplies particles to the magnetotail, the ion current periodically updates the magnetic field using the Biot-Savart law. The simulated magnetotail evolves into a quasi-steady state, characterized by the periodic motion of the model's near-Earth X-line. This variability results from the nonadiabatic acceleration of ions in the current sheet and their rapid loss from the tail. The characteristic time scale of variability in the magnetotail is on the order of 4 - 5 minutes. We also investigate how the magnetotail's topology responds to increased convection electric fields, and show examples of observations of variability in the magnetotail.

Peroomian, Vahe↗
NASA NTRS1999

Intrinsic Variability in the Quiet-Time Magnetotail

This study investigates the evolution of the magnetotail's magnetic field with the aid of a self-consistent two-dimensional model in which the ion current periodically updates the magnetic field. The plasma mantle supplies particles continuously to the magnetotail, and the perturbation magnetic field is calculated from the ion current using the Biot-Savart law. The simulated magnetotail evolves into a quasi-steady state, characterized by the periodic motion of the near-Earth X-line in the model. This variability is caused by the nonadiabatic acceleration of ions in the current sheet and their rapid loss from the tail. Particularly noteworthy is the value found for the characteristic time scale of variability in the magnetotail. on the order of 4 - 5 minutes.

Peroomian, Vahe↗
NASA NTRS1998

Self-Consistent Simulation of the Magnetotail

Kinetic effects may be critically important at various stages of magnetotail evolution prior to and after the break up of substorms. The quasi-adiabaticity of ion dynamics results in the appearance of pronounced off diagonal terms in the pressure tensor (an effect that cannot be reproduced using the standard MHD (magnetohydrodynamic) approach). Only the appearance of these terms could support the formation of thin current sheets that recent experimental data have repeatedly indicated. We present in this paper the results of a self-consistent large-scale kinetic simulation of the Earth's magnetotail. We launch ions from the plasma mantle and self-consistently adjust the background magnetic field by computing the perturbations magnetic field from the particle current. We find that a thin current sheet with a half-thickness of approximately 0.3 R(sub E) quickly develops in the simulation. Also, the magnetotail evolves into a periodic state where the location of the X-line in the tail oscillates between x approximately 40 R(sub E) and x approximately 70 R(sub E) on a 5-minute time scale. Evidence of this periodic motion is also seen in the auroral precipitation profile of ions.

Peroomian, Vahe↗
NASA NTRS1994

Consequences of magnetotail ion dynamics

The trajectories of a large ensemble of particles are calculated in a modified Tsyganenko magnetic field model with a uniform cross-tail electric field. The model magnetotail can be divided into several distinct dynamical regimes of ion motion. Near Earth, where the field lines are dipolar the adiabatic formalism is adequate. In the mid-tail and distant tail, guiding-center theory breaks down and must be replaced by a quasi-adiabatic formalism. There is an important transition region between the adiabatic and quasi-adiabatic regions where ion trajectories become more complicated and no simple analytical description holds. This wall region is characterized by rapid ion acceleration and a major loss of particles to the dusk flank. The moments of the ion distribution function are constructued from the ion trajectories, including density, temperature, and pressure in the x-z and x-y planes. In the noon-midnight meridian plane, parameters are relatively constant except near the Earth, while the x-y plots show strong gradients across the magnetotail. Magnetotail plasma convects earthward, drifts toward dusk, and is squeezed out of the tail in the near-Earth region. A thin current sheet forms in the quasi-adiabatic region, and the pressure tensor has significant off-diagonal terms at its edges. These terms are the result of quasi-adiabatic ion trajectories which lead to azimuthally asymmetric distribution functions capable of maintaining approximate stress balance across the current sheet. Simplified analytical descriptions provide further physical insight into ion dynamics that are observed.

Ashour-Abdalla, Maha↗
NASA NTRS1993

Shaping of the magnetotail from the mantle - Global and local structuring

Kinetic modeling of the properties of magnetotail formation from a plasma mantle source are discussed, and a unified view of the structure of the central part of the magnetotail plasma sheet as well as the structure of its boundary layer is developed. The Tsyganenko magnetic field model for quiet periods of magnetospheric activity is used to trace trajectories of mantle protons in the presence of a uniform dawn-dusk electric field. The present model shows the evolution of the global structure of the tail with a clearly defined central plasma sheet and plasma sheet boundary layer developing from its beginnings as a plasma 'nucleus' in the distant tail current sheet. This large-scale restructuring is accompanied by the creation of small-scale features in the particle distribution functions. It is also shown that complementary ring distribution structures should also exist in the central plasma sheet. The ion distribution functions in the central plasma sheet should take a rather specific form in velocity space with loss regions oriented predominantly orthogonal to the magnetic field.

Ashour-Abdalla, Maha↗
NASA NTRS1992

The formation of the wall region - Consequences in the near earth magnetotail

This paper discusses important new findings obtained from global kinetic simulations of magnetotail plasma. A region of strongly nonadiabatic ion acceleration (known as the wall region) exists in the near earth tail and demarcates two very different regimes of ion motion: adiabatic and quasi-adiabatic. A strong enhancement of the cross-tail current occurs on the tailward side of the wall. A comparison of numerical and adiabatic pressure profiles indicates that nonadiabatic processes operating in this region may contribute significantly to a pressure balance relief in the course of quasi-steady magnetospheric convection.

Ashour-Abdalla, Maha↗