arXiv subjects

C. H. Jaroschek

Publications and source records attributed to C. H. Jaroschek.

12 recordsLinked to original sources

arXiv2008

Deformation of electron holes in phase space as prerequisite for narrow band maser emission: A qualitative discussion

A qualitative discussion is given of the role electron holes play in generating fine structure on the electron cyclotron maser radiation. It is argued that electron holes become deformed in phase space when interacting with an incomplete ring or horseshoe distribution which occurs in the presence of strong field aligned electric fields in the upward current region and in the presence of a loss cone. This interaction is based on momentum balance considerations. Deformed narrow electron holes cause steep velocity space gradients on the ring distribution that lead to intense but narrow band emission from their high speed sides and absorption at slightly higher frequency from their low speed sides. The twins of banded emission and absorption move in frequency space due to the average real space displacement of the deformed electron hole.

physics.space-ph↗

arXiv2008

Auroral evidence for multiple reconnection in the magnetospheric tail plasma sheet

We present auroral evidence for multiple and, most probably, small scale reconnection in the near Earth magnetospheric plasma sheet current layer during auroral activity. Hall currents as the source of upward and downward field-aligned currents require generation of the corresponding electron fluxes. The auroral spatial ordering in a multiple sequence of these fluxes requires the assumption of the existence of several -- and possibly -- even many tailward reconnection sites.

physics.space-ph↗

arXiv2008

On deformation of electron holes in phase space

This Letter shows that for particularly shaped background particle distributions momentum exchange between phase space holes and the distribution causes acceleration of the holes along the magnetic field. In the particular case of a non-symmetric ring distribution (ring with loss cone) this acceleration is nonuniform in phase space being weaker at larger perpendicular velocities thus causing deformation of the hole in phase space.

physics.space-ph↗

arXiv2008

Planetary Bow Shocks

Our present knowledge of the properties of the various planetary bow shocks is briefly reviewed. We do not follow the astronomical ordering of the planets. We rather distinguish between magnetised and unmagnetised planets which groups Mercury and Earth with the outer giant planets of the solar system, Mars and Moon in a separate group lacking magnetic fields and dense atmospheres, and Venus together with the comets as the atmospheric celestial objects exposed to the solar wind. Asteroids would, in this classification, fall into the group together with the Moon and should behave similarly though being much smaller. Extrasolar planets are not considered as we have only remote information about their behaviour. The presentation is brief in the sense that our in situ knowledge is rather sporadic yet, depending on just a countable number of bow shock crossings from which just some basic conclusions can be drawn about size, stationarity, shape and nature of the respective shock. The only bow shock of which we have sufficient information to deal in sufficient depth with its physics is Earth's bow shock. This has been reviewed in other places in this volume and therefore is mentioned here only as the bow shock paradigm in passing.

astro-ph↗

arXiv2008

The Heliospheric Termination Shock

The heliospheric Termination Shock is the largest (by dimension) shock in the heliosphere. It is believed that it is also the strongest shock and is responsible for the generation of the Anomalous Cosmic Ray component in the heliosphere. This chapter review the gross properties and observations of the Termination Shock. It is structured as follows: 1. The heliosphere, providing the heliospheric stage for Termination Shock formation, 2. The argument for a heliospheric Termination Shock, 3. The global heliospheric system, 4. Termination Shock properties, 5. Observations: the Voyager passages, radio observations, plasma waves and electron beams, traces of plasma and magnetic field, energetic particles, galactic cosmic rays, Termination Shock particles, the anomalous cosmic ray component, 6. Conclusions.

astro-ph↗

arXiv2008

Fundamentals of Non-relativistic Collisionless Shock Physics: V. Acceleration of Charged Particles

A comprehensive review is given of the various processes proposed for accelerating particles by shocks to high energies. These energies are limited by several bounds: the non-relativistic nature of the heliospheric collisionless shocks to which this review restricts, the finite size of these shocks, the finite width of the downstream region, and to the nature of turbulence. In general, collisionless shocks in the heliosphere cannot accelerate particles to very high energies. As a fundamental problem of the acceleration mechanism the injection of see particles is identified. Some mecchanisms for production of seed particles are invoked. Acceleration of electrons begins to uncover its nature. The following problems are covered in this chapter: 1. Introduction -- first and second order Fermi acceleration, 2. Accelerating ions when they are already fast, diffusive acceleration, convection diffusion equation, Lee's self-consistent quasilinear shock acceleration model, 3. Observations, 4. The injection problem, ion surfing, test particle simulations, self-consistent shock acceleration simulations, downstream leakage, trapped particle acceleration, 5. Accelerating electrons, Sonnerup-Wu mechanism, Hoshino's electron shock surfing on quasi-perpendicular shocks, quasiparallel shock surfing.

astro-ph↗

arXiv2008

Fundamentals of Non-relativistic Collisionless Shock Physics: IV. Quasi-Parallel Supercritical Shocks

1. Introduction, 2. The (quasi-parallel) foreshock; Ion foreshock, Ion foreshock boundary region; Diffuse ions;Low-frequency upstream waves; Ion beam waves; The expected wave modes; Observations; Diffuse ion waves; Electron foreshock; Electron beams; Langmuir waves; stability of the electron beam; Electron foreshock boundary waves; Nature of electron foreshock waves; Radiation; Observations; Interpretation; 3. Quasi-parallel shock reformation; Low-Mach number quasi-parallel shocks; Turbulent reformation; Observations; Simulations of quasi-parallel shock reformation; Hybrid simulations in 1D; Hybrid simulations in 2D; Full particle PIC simulations; Conclusions; 4. Hot flow anomalies; Observations; Models and simulations; Solitary shock; 5. Downstream region; 6. Summary and conclusions.

astro-ph↗

arXiv2008

Fundamentals of Non-relativistic Collisionless Shock Physics: I. The Shock Problem

The problem of collisionless shocks is posed as the problem of understanding how in a completely collisionless streaming high-temperature plasma shocks can develop at all, forming discontinuous transition layers of thickness much less than any collisional mean free path length. The history of shock research is briefly reviewed. It is expressed that collisionless shocks as a realistic possibility of a state of matter have been realized not earlier than roughly half a centruy ago. The basic properties of collisionless shocks are noted in preparing the theory of collisionless shocks and a classification of shocks is given in terms of their physical properties, which is developed in the following chapters. The structure of this chapter is as follows: 1. A cursory historical overview, describing the early history, gasdynamic shocks, the realisation of the existence of collisionless shocks and their investigation over three decades in theory and observation until the numerical simulation age, 2. Posing the shock problem as the question: When are shocks? 3. Types of collisionless shocks, describing electrostatic shocks, magnetized shocks, MHD shocks, shock evolutionarity and coplanarity, switch-on and switch-off shocks, 4. Criticality, describing the transition from subcritical dissipative to supercritical viscose shocks, 5. Remarks.

astro-ph↗

arXiv2008

Fundamentals of Non-relativistic Collisionless Shock Physics: II. Basic Equations and Models

This paper develops the basic sets of equations which lead to the conservation laws describing collisionless plasma shock waves. We discuss the evolution of shock waves by wave steepening, derive the Rankine-Hugoniot conditions for magnetogasdynamic shocks, discuss various analytical models of shock formation, and discuss the basic instabilities which may become important in collisionless shock physics. We then present a survey of the theory of anomalous resistivity in the quasilinear limit and beyond and discuss mechanisms of shock particle reflection as far as they have been investigated in the published literature. The content of the chapter is the following: 1. Wave steepening, describing simple waves and steepening due to nonlinearity, balnced by dissipation in Burgers' shocks, by dispersive effects in the Korteweg-de Vries equation, the Sagdeev-Potential method, 2. Basic equations, presenting kinetic theory and the transition to moment equations in the fluid description, 3. Rankine-Hugoniot relations, giving the jump conditions across shocks, explicit MHD solution for perpendicular shocks and parallel shocks, and high Mach number conditions, 4. Waves and instabilities, giving the general dispersion relation, describing low-$β$-shocks, whistler and Alfvén shocks, the various shock-relevant instabilities, 5. Anomalous transport for the various electrostatic wave-particle interactions, general description of anomalous resistivity, shock particle reflection from potential and specularly, hole formation, 6. Briefing on numerical simulation techniques, giving a short idea on this important field and its methods.

astro-ph↗

arXiv2008

Fundamentals of Non-relativistic Collisionless Shock Physics: III. Quasi-Perpendicular Supercritical Shocks

The theory and simulations of quasi-perpendicular and strictly perpendicular collisionless shocks are reviewed. The text is structured into the following sections and subsections: 1. Setting the frame, where the quasi-perpendicular shock problem is formulated, reflected particle dynamics is described in theoretical terms, foot formation and foot ion acceleration discussed, and the shock potential explained. 2. Shock structure, 3. Ion dynamics, describing its role in shock reformation and the various ion-excited instabilities. 4. Electron dynamics, describing electron instabilities in the foot; 5. The problem of stationarity, posing the theoretical reasons for shocks being non-stationary, discussing nonlinear whistler mediated variability, two-stream and modified two-stream variability, formation of ripples in two-dimensions, 6. Summary and conclusions: The possibility of shock breaking.

astro-ph↗

arXiv2008

Gibbsian theory of power law distributions

It is shown that power law phase space distributions describe marginally stable Gibbsian equilibria far from thermal equilibrium which are expected to occur in collisionless plasmas containing fully developed quasi-stationary turbulence. Gibbsian theory is extended on the fundamental level to statistically dependent subsystems introducing an `ordering parameter' $κ$. Particular forms for the entropy and partition functions are derived with super-additive (non-extensive) entropy, and a redefinition of temperature in such systems is given.

physics.plasm-ph↗

arXiv2005

Giant Radio Pulses from the Crab Pulsar

Individual giant radio pulses (GRPs) from the Crab pulsar last only a few microseconds. However, during that time they rank among the brightest objects in the radio sky reaching peak flux densities of up to 1500 Jy even at high radio frequencies. Our observations show that GRPs can be found in all phases of ordinary radio emission including the two high frequency components (HFCs) visible only between 5 and 9 GHz (Moffett & Hankins, 1996). This leads us to believe that there is no difference in the emission mechanism of the main pulse (MP), inter pulse (IP) and HFCs. High resolution dynamic spectra from our recent observations of giant pulses with the Effelsberg telescope at a center frequency of 8.35 GHz show distinct spectral maxima within our observational bandwidth of 500 MHz for individual pulses. Their narrow band components appear to be brighter at higher frequencies (8.6 GHz) than at lower ones (8.1 GHz). Moreover, there is an evidence for spectral evolution within and between those structures. High frequency features occur earlier than low frequency ones. Strong plasma turbulence might be a feasible mechanism for the creation of the high energy densities of ~6.7 x 10^4 erg cm^-3 and brightness temperatures of 10^31 K.

astro-ph↗