Ordinary-mode electromagnetic instability in counterstreaming plasmas with anisotropic temperatures
Electromagnetic linearly polarized mode instability in counterstreaming plasmas with anisotropic temperatures using Vlasov equation
Bornatici, M.↗
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Ring current instabilities in the magnetohydrodynamic frequency range
This report summarizes recent theoretical developments in ring current plasma instabilities in the magnetohydrodynamic (MHD) frequency range but with the effect of finite Larmor radius, and discusses its relevance to satellite-based observations. Possible instabilities are the bounce resonant instabilities caused by a humped energy distribution, the drift mirror instability caused by an anisotropic pressure and the drift wave type instability caused by a combination of drift-bounce resonance and reduced Alfven frequency due to a high beta loading of the flux tube. Here, beta is proportional to plasma/magnetic pressures. Mechanisms leading to turbulence are also discussed.
Hasegawa, A.↗
An Overview of Scientific and Space Weather Results from the Communication/Navigation Outage Forecasting System (C/NOFS) Mission
The Communication/Navigation Outage Forecasting System (C/NOFS) Mission of the Air Force Research Laboratory is described. C/NOFS science objectives may be organized into three categories: (1) to understand physical processes active in the background ionosphere and thermosphere in which plasma instabilities grow; (2) to identify mechanisms that trigger or quench the plasma irregularities responsible for signal degradation; and (3) to determine how the plasma irregularities affect the propagation of electromagnetic waves. The satellite was launched in April, 2008 into a low inclination (13 deg), elliptical (400 x 850 km) orbit. The satellite sensors measure the following parameters in situ: ambient and fluctuating electron densities, AC and DC electric and magnetic fields, ion drifts and large scale ion composition, ion and electron temperatures, and neutral winds. C/NOFS is also equipped with a GPS occultation receiver and a radio beacon. In addition to the satellite sensors, complementary ground-based measurements, theory, and advanced modeling techniques are also important parts of the mission. We report scientific and space weather highlights of the mission after nearly four years in orbit
Pfaff, R.↗
Nonlinear magnetosonic waves and mirror mode structures in the March 1991 Ulysses interplanetary event
In examining the March 23-25, 1991 Ulysses (2.2 AU) high speed solar wind events, two distinct plasma wave modes are found: steepened magnetosonic waves with whistler precursors and mirror mode structures. These two modes are locally generated by plasma instabilities, presumably associated with anisotropies existing in the energetic shock particles and solar wind plasma, respectively. The magnetosonic waves are generated by a right-hand resonant instability associated with an about 40 keV ion beam. By an extrapolation of the results presented here, assuming microflares and nanoflares at the sun generate shocks in the lower corona and these shocks accelerate energetic ions, it is suggested that the ions, via the right-hand resonant instability, generate magnetosonic waves which steepened to form 'microshocks'. These shocks could, in turn, accelerate more energetic ions, leading to a shock/energetic ion/magnetosonic wave cascade. These newly formed magnetosonic waves and shocks presumably could propagate in a broad range of directions, leading to energy dissipation over a large region of the outer corona.
Tsurutani, Bruce T.↗
Effect of compressibility on kelvin-helmholtz instability in a plasma.
Compressibility effect on kelvin-helmholtz instability for cases of stiff plasma and lumpy plasma
PLASMA STABILITY↗
On the Necessity and Feasibility of an Equatorial Magnetospheric Constellation
Synthesizing multi-point in-situ observations from the magnetosphere is the only way that we can retain an accurate knowledge of the driving mechanisms of convection and energy flow while "imaging" its vast volume. In addition to measuring the wavenumber of plasma instabilities thus opening up for study a previously unexplored domain of space plasma physics the Constellation mission can afford us a view of the rapid topological reconfigurations and the energy circulation throughout the astrophysical laboratory closest to human space activity. In this paper we argue that the deployment of approximately 80 autonomous micro-satellites (probes) to monitor the Earth's magnetosphere and measure the plasma and magnetic field in the near-equatorial magnetosphere is a necessary and sufficient condition for answering long standing, high priority questions regarding magnetospheric stability and dynamics. The proposed mission concept is technically feasible and fiscally modest. The probes can be raised from a Geosynchronous Transfer orbit to their final elliptical orbits with perigee approximately 3R(sub E)and apogees ranging from 12 to 42 R(sub E) by a single dispenser propelled by an ion engine. Each probe will weigh approximately 5 kg. The mission can form a cornerstone of an incrementally deployed Solar Terrestrial Probe Line Magnetospheric Constellation, as it requires no new technologies in the areas of spacecraft subsystems and instruments, but some development in the areas of dispenser design, probe packaging, mechanical release and spin-up. The technology developed can be utilized by follow-on Constellation class missions as well.
Angelopoulos, V.↗
Collisional interchange instability. II - A comparison of the numerical simulations with the in situ experimental data
A two-dimensional model applicable to F region ionosphere plasma instabilities has been developed and described in a companion paper. Here the model is applied to equatorial F region irregularities and is tested against rocket and satellite data. As a diagnostic, simulated data sets are created which are similar to the one-dimensional measurements of plasma density performed by space probes and the Fourier transform of these data is taken in the same manner and used by the space experimentors. Unlike previous simulations of this phenomenon, an inherent anisotropy is found in the instability development which is mirrored in the in situ data. Evidence that the shallow spectral slopes which often characterize spread F rocket spectra near the F peak may be due to a change in the angle between the rocket velocity vector and the characteristic directions in the medium is presented.
Kelley, M. C.↗
Thermal instability of a radiative and resistive coronal plasma
Thermal instability is believed to determine the evolution and formation of cool structures in the solar atmosphere such as the transition region and prominences (or filaments). The linear modes that arise in a sheared, force-free, magnetic field due to thermal instability are studied numerically. Previous studies have considered separately modes that arise due to the effects of radiation, compression, anisotropic thermal conduction, and ohmic heating. Here the results of such studies are integrated, first by presenting simple arguments that illustrate the essential physics of ideal, sheared-field, condensation modes, and second by showing numerically how finite resistivity affects the condensational instability in parameter regimes applicable to the solar corona.
Sparks, L.↗
Numerical simulation of the generation of electrostatic turbulence in the magnetotail
A two-dimensional plasma model is used to investigate the development of electrostatic turbulence in a magnetized plasma from plasma instabilities. The simulation consists of following the motion of 100,000 ions in their self-consistent electrostatic field. The electrons are treated as a constant neutralizing background. The instabilities modeled are driven by a ring-type velocity distribution and by interpenetrating ion beams in a time-variable magnetic field. Instability growth times are of the order of an ion gyroperiod in the case of the ring distribution and of the order of an ion plasma period in the case of the beam simulation. Maximum potential differences generated are of the order of the ion kinetic energies. These simulations demonstrate the cascade of wave energy to long wavelengths, thus showing the E x B turbulence can be generated from plasma microinstabilities. After the free energy feeding, the instabilities are exhausted, and wave energy at wavelengths less than an ion gyrodiameter decays quickly to equilibrium levels, while longer wavelength modes persist for much longer times. In one model with a time dependent, but spatially uniform, magnetic field the electric field energy at long wavelengths appeared to increase as a result of the increase of the magnetic field.
Swift, D. W.↗
Kelvin-helmholtz instability in an anisotropic plasma.
Kelvin-Helmholtz instability due to tangential discontinuity of velocities between two streams of anisotropic plasma, noting monotonic and growing- wave instabilities
PLASMA STABILITY↗
Solar wind pickup of ionized Venus exosphere atoms
Previous calculations of electrostatic and electromagnetic growth rates for plasma instabilities have neglected the thermal spread of the distribution function of the planetary ions. We consider the effects of finite temperatures for exospheric ions borne in the solar wind. Specifically, growth rates are calculated for electromagnetic instabilities in the low-frequency case for Alfven waves and the intermediate frequency case for whistlers. Also, electrostatic growth rates are calculated for the intermediate frequency regime. From these growth rates, estimates are derived for the pickup times of the planetary ions. The electromagnetic instabilities are shown to produce the most rapid pickup. In the situation where the angle between the local Venus magnetic field and the plasma flow direction is small, the pickup times for both electromagnetic and electrostatic instabilities become very long. A possible consequence of this effect is to produce regions of enhanced planetary ion density in favorable Venus magnetic field-solar wind flow geometries.
Curtis, S. A.↗
Compositional changes, time and density variations in the magnetosphere associated with Birkeland currents and particle acceleration
Birkeland currents, parallel electric fields and plasma instabilities often occur together in time and space and play an important role in large scale plasma motions between the ionosphere and magnetosphere and along the magnetic field in the magnetosphere. The results of the plasma movements are large density and composition variations in the ionosphere and magnetosphere. Observations from ISIS-2 at 1400 km altitude show large densities with heavy ions dominating in regions with upward Birkeland currents, and low densities and light ions in regions with downward currents. Observations from ISEE-1 in field aligned current regions at 10,000 to 15,000 km altitude show transverse heating of protons and oxygen ions to 250 eV. Because of the different mobility of the protons and oxygen ions the proton flow is important in the beginning of the events but later the outflow becomes almost pure oxygen. Similarly ISEE-1 observations of outgoing field ion beams at 10,000 to 15,000 km altitude show time variations in the H+/O+ ratios and a dominance of O+ later in the events.
Ungstrup, E.↗
Shuttle Orbiter tethered subsatellite for exploring and tapping space plasmas
Consideration is given to the possibilities for studies in space plasma physics offered by a subsatellite mechanically tethered above the Space Shuttle Orbiter by a long conducting wire. The proposed experiment, designated the Shuttle Electrodynamic Tether Systems (SETS) is based on the concept of collecting electrons at the subsatellite and ejecting them from the Orbiter, made possible by the emf generated by the motion of the tether across geomagnetic field lines. The power generated in this manner can be used both for practical purposes within the Orbiter and for the creation of large-amplitude plasma and electromagnetic waves within the surrounding plasma. For a conducting spherical subsatellite 30 m in diameter with a 10-km tether drawing 1 A, calculations show that emfs on the order of 1000-2000 V and energy dissipation of as much as 10,000 W can be obtained, accompanied by the generation of two regions of net electric charge in the ionosphere. Scientific studies considered for SETS include the measurement of MHD waves artificially generated in the ionosphere, the investigation of current-driven plasma instabilities, VLF wave generation and the simulation of electrodynamics associated with the motion of celestial bodies through plasma.
Banks, P. M.↗
Plasma emission from isotropic Langmuir turbulence - Are radio microbursts structureless?
The brightness temperature of radio emission through the fundamental and second harmonic plasma processes is determined for isotropic Langmuir waves of low-energy density in order to account for the microbursts at meter-dekameter wavelengths. The probable cause for low levels of Langmuir turbulence is the presence of isotropic density fluctuations in the corona which isotropize the beam-generated Langmuir waves. We determined the energy density of Langmuir waves attainable from the beam-plasma instability in the presence of isotropic density fluctuations. Since the electron density fluctuations isotropize the beam-generated plasma waves, the head-on collision of plasma waves becomes efficient to produce the second harmonic plasma emission. For reasonable beam parameters, the brightness temmperature of the fundamental never exceeds 10 exp 6 K, while the second harmonic covers the observed range of microburst brightness temperatures. Thus, the microbursts are predominantly at second harmonic. This leads to an important conclusion that the microbursts are structureless, similar to a population of normal type III bursts of low polarization with no fundamental-harmonic structure.
Gopalswamy, N.↗
Modeling of the Convection and Interaction of Ring Current, Plasmaspheric and Plasma Sheet Plasmas in the Inner Magnetosphere
Distinctive sources of ions reside in the plasmasphere, plasmasheet, and ring current regions at discrete energies constitute the major plasma populations in the inner/middle magnetosphere. They contribute to the electrodynamics of the ionosphere-magnetosphere system as important carriers of the global current system, in triggering; geomagnetic storm and substorms, as well as critical components of plasma instabilities such as reconnection and Kelvin-Helmholtz instability at the magnetospheric boundaries. Our preliminary analysis of in-situ measurements shoves the complexity of the plasmas pitch angle distributions at particularly the cold and warm plasmas, vary dramatically at different local times and radial distances from the Earth in response to changes in solar wind condition and Dst index. Using an MHD-ring current coupled code, we model the convection and interaction of cold, warm and energetic ions of plasmaspheric, plasmasheet, and ring current origins in the inner magnetosphere. We compare our simulation results with in-situ and remotely sensed measurements from recent instrumentation on Geotail, Cluster, THEMIS, and TWINS spacecraft.
Fok, Mei-Ching↗
Plasma wave turbulence at the magnetopause - Observations from ISEE 1 and 2
An investigation of plasma wave electric and magnetic fields in the vicinity of the magnetopause using measurements from the ISEE 1 and 2 spacecraft is presented. Strong electric and magnetic field turbulence is often observed at the magnetopause; the electric field spectrum of this turbulence extends from less than a few hertz to over 100 kHz, and the magnetic field from a few hertz to about 1 kHz. Similar turbulence spectra are observed in association with flux transfer events and possible 'inclusions' of boundary layer plasma in the magnetosphere. Two possible plasma instabilities, the electrostatic ion-cyclotron and the lower-hybrid-drift instability, should explain the broad-band electric field turbulence; the narrow-band electrostatic emissions near the local electron plasma frequency are believed to be plasma oscillations or electrostatic waves near the upper-hybrid-resonance frequency.
Gurnett, D. A.↗
Nonlinear energy flow in a beam-plasma system
The three-dimensional character of the beam-plasma instability is investigated. The true beam-electron distribution function is resolved with a novel directional energy analyzer. The electron plasma waves are observed to develop a large spread in perpendicular wave numbers and damp in a relatively short distance producing an energetic electron tail on the background distribution. The damping is believed to be due to strong ion fluctuations which produce an anomalous resistivity.
Whelan, D. A.↗
Safety First: Stability and Dissipation of Line-tied Force-free Flux Tubes in Magnetized Coronae
Abstract Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes ( m = 1) and efficient magnetic energy dissipation develop for plasma safety factors q ≲ 1, where q is the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes ( m > 1) can distort equilibrium flux tubes for q > 1 but induce significantly less dissipation. In our analysis, the characteristic pitch μ ˜ 0 of flux-tube field lines determines the growth rate ( ∝ μ ˜ 0 3 ) and minimum wavelength of the kink instability ( ∝ μ ˜ 0 − 1 ). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given μ ˜ 0 . By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions.
79 ASTRONOMY AND ASTROPHYSICS↗