Robert Rankin

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Low‐Energy (<200 eV) Electron Acceleration by ULF Waves in the Plasmaspheric Boundary Layer: Van Allen Probes Observation

Journal of Geophysical Research: Space Physics, 2017

We report observational evidence of cold plasmaspheric electron (<200 eV) acceleration by ultr... more We report observational evidence of cold plasmaspheric electron (<200 eV) acceleration by ultralow frequency (ULF) waves in the plasmaspheric boundary layer on 10 September 2015. Strongly enhanced cold electron fluxes in the energy spectrogram were observed along with second harmonic mode waves with a period of about 1 min which lasted several hours during two consecutive Van Allen Probe B orbits. Cold electron (<200 eV) and energetic proton (10–20 keV) bidirectional pitch angle signatures observed during the event are suggestive of the drift‐bounce resonance mechanism. The correlation between enhanced energy fluxes and ULF waves leads to the conclusions that plasmaspheric dynamics is strongly affected by ULF waves. Van Allen Probe A and B, GOES 13, GOES 15, and MMS 1 observations suggest that ULF waves in the event were strongest on the duskside magnetosphere. Measurements from MMS 1 contain no evidence of an external wave source during the period when ULF waves and injected ...

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Role of ionospheric effects and plasma sheet dynamics in the formation of auroral arcs

Space Science Reviews

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Alternating Direction Implicit Methods on Distributed and Shared Memory Parallel Computers

High Performance Computing Systems and Applications, 1998

Global scale simulation codes capable of modeling the interaction of the solar wind with the Eart... more Global scale simulation codes capable of modeling the interaction of the solar wind with the Earth’s magnetosphere are being developed by the international space community. We shall describe different implementations of a 3D alternating direction implicit (ADI) magnetohydrodynamic (MHD) simulation code on distributed and shared memory parallel and parallel/vector computers. The specific architectures considered are the IBM SP and Silicon Graphics Origin, and techniques appropriate to Cray-class computers. On the distributed memory IBM SP, the ADI code was run under PVMe and MPI, and gave good scalability under a single program multiple data (SPMD) implementation. Scalability on the SGI Origin was approximately linear up to the available configuration size of 128 processors, with a change in slope at 32 processors. On Cray-class computers, very high efficiencies are possible when vectorization is combined with parallel processing. It is shown that while this leads to near optimum performance, it is achieved at the expense of increased memory requirements.

Drift-resonant acceleration of electrons in response to impulse-excited ULF waves

Auroral substorm dynamics and field line resonances

Earth, Planets and Space, 2002

Magnetospheric substorms frequently have oscillating auroral phenomena associated with them, and ... more Magnetospheric substorms frequently have oscillating auroral phenomena associated with them, and which may be related to field line resonances. In this paper we present an analysis of photometer data which displays such oscillations in luminosity. We use data from the Gillam station in the CANOPUS array for April 1, 2000. Clear pulsations in magnetometer and photometer data are observed at 2.2 mHz. The latitudinal distribution of the photometer pulsations indicates that the auroral luminosity variations, caused by precipitating electrons and protons, are modulated by large scale global compressional modes (field line resonances). The proton and electron auroras were found to oscillate essentially out of phase. As well, the variation of phase across the peak in the luminosity resonance follows the pattern expected for the coupling of resonant Alfvén modes by normal compressional modes in the magnetotail.

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Dayside Aurora and Auroral Conjugacy

nationalacademies.org

This white paper discusses the scientific significance of dayside and conjugate auroras. The days... more

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Stability of electron inertia Alfvén solitons

Journal of Plasma Physics, 1992

Das, Kamp and Sluijter have proposed equations describing three-dimensional electron inertia Alfv... more Das, Kamp and Sluijter have proposed equations describing three-dimensional electron inertia Alfvén waves for which the characteristic length scales in directions parallel and perpendicular to the ambient magnetic field are of the same order. Planar, obliquely propagating soliton solutions of these equations are known to be linearly unstable. Numerical simulations reveal the nonlinear phase of the evolution of these solitons: a transition from flat to cylindrical solitons is observed, followed by breaking-up into three-dimensional localized cavities. The final stage corresponds to wave breaking; no final stable structure is achieved within the model.

Modeling the relationship between substorm dipolarization and dispersionless injection

Journal of Geophysical Research: Space Physics, 2011

Significant populations of electrons with energies of tens of keV appear in the Earth's inner cen... more Significant populations of electrons with energies of tens of keV appear in the Earth's inner central plasma sheet during the substorm expansion phase. Increasing observational evidence indicates that these injections begin at a radially narrow but azimuthally extended transition between very stretched and less stretched field lines around 8 R E . In this work we suggest that the tailward retreat of this transition region can be responsible for adiabatic acceleration of electrons which is sufficient to cause ionospheric signatures of the dispersionless injections observed by riometers. To support this mechanism we develop a novel conceptual magnetotail magnetic field model with a few adjustable parameters which can be easily constrained by observations. Our calculations show that a tailward motion of the transition region at the speed of 0.8 R E /min is required to achieve good agreement with riometer observations.

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Electrodynamics of magnetosphere-ionosphere coupling and feedback on magnetospheric field line resonances

Journal of Geophysical Research: Space Physics, 2007

We present a new dynamic model that describes coupling between standing inertial or ion-acoustic-... more We present a new dynamic model that describes coupling between standing inertial or ion-acoustic-gyroradius-scale shear Alfve ´n waves, compressional modes, and auroral density disturbances. The model is applied to the excitation of field line resonances (FLRs) in dipolar and stretched geomagnetic fields in Earth's magnetosphere. Magnetosphereionosphere coupling is included by accounting for the closure of magnetospheric fieldaligned currents (FACs) through Pedersen currents in the ionosphere. A second new aspect is that the height-integrated Pedersen conductivity is treated as a dynamic parameter by electrodynamically coupling the two-dimensional finite element wave model ''Topo'' to the ionospheric ionization model ''Global Airglow Model (GLOW).'' We demonstrate that field line stretching brings the equatorial plasma b above unity, where the reduced MHD formulism for low-frequency plasma breaks down. As an application of our model, we study a specific FLR event observed on 31 January 1997, when the NASA FAST satellite was over the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) Gillam station. Using geomagnetic fields computed from the T96 magnetic field model, we show that auroral electron precipitation produces strong Pedersen conductivity enhancements that control the final amplitude and width of the excited FLR, along with the amplitude of associated density fluctuations. The predictions of the model are generally consistent with observations of this event.

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Effects of shock parameters on upstream energetic electron burst events

Journal of Geophysical Research: Space Physics, 2008

Recent simulation results have revealed that energetic electron bursts are produced cyclically at... more Recent simulation results have revealed that energetic electron bursts are produced cyclically at the shock reformation period upstream of reforming shocks and are qualitatively very different from the continuous beam expected from time‐stationary shocks (Yuan et al., 2007a). This paper extends our previous studies by numerically investigating the dependence of electron burst events on shock parameters (the upstream plasma β and Mach number MA). The test particle approximation is made for electrons, and the electron trajectories are traced exactly in the time‐dependent electromagnetic field profiles, generated by one‐dimensional hybrid simulation code. Simulation results indicate that the upstream incoming electrons can be reflected nonuniformly or continuously depending on the shock parameters. Bursty energetic electron events take place when the plasma beta is low (β ≤ 0.4) and the shock Mach number is high (MA ≥ 6). Time‐varying loss cone, beam, and ring beam features are observe...

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Electromagnetic waves generated by ionospheric feedback instability

Journal of Geophysical Research: Space Physics, 2008

A new interactive M‐I coupling model that describes the dynamic interaction between magnetospheri... more A new interactive M‐I coupling model that describes the dynamic interaction between magnetospheric dispersive waves, compressional modes, and auroral electron precipitations is applied to investigate the geomagnetic electromagnetic pulsations observed in Earth's magnetosphere in terms of magnetospheric waves triggered by ionospheric feedback instability. Two new aspects of this work are that (1) we treat the full nonlinear MHD equations, i.e., include the full compressional modes and their coupling with shear Alfvén waves in the magnetosphere; and (2) the height‐integrated Pedersen conductivity is treated as a dynamic parameter by electrodynamically coupling the 2D finite element wave model “TOPO” to the ionospheric ionization model “GLOW”. It is shown that the feedback instability can be triggered by a very small‐scale, small amplitude density perturbation; and the small‐scale electromagnetic oscillations and their associated density fluctuations observed in magnetosphere can b...

Do magnetospheric shear Alfvén waves generate sufficient electron energy flux to power the aurora?

Journal of Geophysical Research: Space Physics, 2010

Using a self‐consistent drift‐kinetic simulation code, we investigate whether electron accelerati... more Using a self‐consistent drift‐kinetic simulation code, we investigate whether electron acceleration owing to shear Alfvén waves in the plasma sheet boundary layer is sufficient to cause auroral brightening in the ionosphere. The free parameters used in the simulation code are guided by in situ observations of wave and plasma parameters in the magnetosphere at distances >4 RE from the Earth. For the perpendicular wavelength used in the study, which maps to ∼4 km at 110 km altitude, there is a clear amplitude threshold which determines whether magnetospheric shear Alfvén waves above the classical auroral acceleration region can excite sufficient electrons to create the aurora. Previous studies reported wave amplitudes that easily exceed this threshold; hence, the results reported in this paper demonstrate that auroral acceleration owing to shear Alfvén waves can occur in the magnetosphere at distances >4 RE from the Earth.

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Open‐closed field line boundary position: A parametric study using an MHD model

Journal of Geophysical Research: Space Physics, 2004

In this paper we investigate the effect of changes in the interplanetary magnetic field (IMF), so... more In this paper we investigate the effect of changes in the interplanetary magnetic field (IMF), solar wind dynamic pressure, and dipole tilt angle on the position of the ionospheric projection of the open‐closed field line boundary (OCB) in a magnetohydrodynamic (MHD) model. We carry out a large number of steady state global MHD simulations in order to parameterize the OCB as a function of the solar wind By and Bz which we find to have the largest effect on the OCB location. We interpolate between the values produced by the simulations, which allows us to evaluate the location of the OCB projection into the ionosphere for any values of ∣By∣ < 10 nT and ∣Bz∣ < 10 nT. It is found that, particularly on the nightside, the OCB position is very sensitive to changes in the northward IMF component Bz, but it is much less sensitive to changes in Bz when it is southward. The response of the OCB location to changes in By also depends greatly on whether Bz is northward or southward, being ...

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Transient ionization time scales for low atomic number elements

Computer Physics Communications, 1985

ABSTRACT

Particle dynamics and energization at the earth bow shock

Particle dynamics and energization at the earth bow shock. 1 RICHARD MARCHAND, FRANCES MACKAY, JI... more Particle dynamics and energization at the earth bow shock. 1 RICHARD MARCHAND, FRANCES MACKAY, JIANYONG LU, KONSTANTIN KABIN, ROBERT RANKIN, University of Alberta -Simulation results are presented for the dynamics and energization of plasma particles as they cross the earth bow shock. The model is based on a kinetic description of particle dynamics, in which single particle trajectories are calculated using a symplectic integration scheme. Particle distribution functions are calculated at different positions in the magnetosheath using Louville's theorem with a Hamiltonian formulation of single particle equations of motion and time reversed particle tracing. As a first approximation, the bow shock is assumed to be represented by a prescribed local plane shock. A more detailed representation of the shock and magnetosheath regions is then considered, as obtained from a global MHD simulation model. Comparisons are made between the two models, for different possible angles between the incident plasma flow velocity and the shock front. Various scenarios of energization are also considered for majority (H) and minority (He and heavier elements) ion species.

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Study of shock nonstationarity with one-and two-dimensional hybrid simulations

Shock reformation involves regions of the shock undergoing periodic collapse and redevelopment on... more Shock reformation involves regions of the shock undergoing periodic collapse and redevelopment on a time scale close to the ion cyclotron period and characteristic transverse spatial scales of order several upstream ion gyroradii. This phenomenon is often observed in computer simulations of high Mach number (MA ), low plasma beta (beta &amp;lt;= 0.4), one-dimensional collisionless shocks. Strong support for the

Resonant Drift Echoes in Electron PSD Produced by Dayside Pc5 Waves following a Geomagnetic Storm

ABSTRACT A model for the interaction between relativistic equatorially mirroring electrons and Pc... more ABSTRACT A model for the interaction between relativistic equatorially mirroring electrons and Pc 5 ULF waves in the magnetosphere is shown to produce drift echoes in electron flux that have characteristics consistent with satellite observations during an episode of strong coherent ULF wave activity. Ground-based observations during an interval of narrow-band ULF activity following a geomagnetic storm on March 24, 1991 are used to constrain the temporal and spatial characteristics of waves produced by the ULF wave model in a dipole geometry. A salient feature of the ULF waves during this interval was the apparent localization of the ULF wave power to the dayside of the magnetosphere, and anti-sunward propagation of ULF wave phase in the morning and afternoon sectors, implying a localized source of ULF wave power close to noon MLT at the magnetopause. The electron dynamics are modeled using these wave fields in order to predict characteristics of the interaction during this event that may be visible in satellite electron flux data. Interpolation of the electron phase space density (PSD) to hypothetical satellite positions and binning in energy shows that the local periodic injection of electrons due to the ULF wave activity results in globally measurable modulations in electron PSD across a range of energy bins. These propagate as drift echoes and become phase mixed as the MLT increases from noon. These drift echoes are strongest for energy ranges that correspond to resonant drift periods, have a periodicity corresponding to that of the ULF waves, and persist at least as long as the ULF wavepacket. A phase shift in the drift echo signals develops between different energy channels as MLT is increased from noon. These qualitative features are reproduced by electron flux observations during the interval on March 24, 1991 from LANL and CRRES satellites.