No abstract

[1] The aurora often breaks down into elongated filaments that are aligned with the geomagnetic field. It is natural to infer from this that when important structures are found in the electrostatic fields they, too, will follow a cylindrical geometry. With ionospheric applications in mind, we have therefore studied the response of the ion distribution function and its transport properties to the sudden introduction of an electric field which increases linearly with radial distance. In this first study we have considered collision-free conditions. We have solved the attendant Boltzmann equation by tracking the ions back in time, thereby using the temporal link between the initial position and velocity of an ion and its position and velocity at an arbitrary time and place. We have obtained a complete analytical solution for the ion trajectories and the ion distribution function, in addition to the transport properties, for all values of time and space. We have found that individual ions gyrate in phase at a frequency other than the conventional gyrofrequency while the associated velocity distribution pulsates at a non-steady rate. Nevertheless, for an initially uniform Maxwellian velocity distribution, the distribution remains Maxwellian for all times, although the drift, density and temperature of that distribution keep changing with time (while staying independent of position). The valuable physical insights gained from the present results will make it feasible to obtain the ion distribution function under more complicated electric field patterns as well as in collisional situations.

We introduce features of propagating ion-acoustic solitons parallel to the magnetic field lines of magnetic flux tubes. A nonlinear model is used. The model considers both isothermal Boltzmann electrons and finite-temperature warm ions. The electrons are composed of two components, background electrons and energetic ones. A soliton-potential equation is obtained for a generalized oblique magnetic field. With a parameterized numerical study, the effect of several parameters on soliton waves is examined. Results show that the shapes of solitons (density, potential and electric field) depend on the driving potential, Mach number, electron density and the relative temperatures among the ions and electrons. The minimum Mach number of solitons and the effect of the Whistler instability are also discussed.

By employing a self-similar, two-fluid MHD model in a cylindrical geometry, we study the features of nonlinear ion-acoustic (IA) waves which propagate in the direction of external magnetic field lines in space plasmas. Numerical calculations not only expose the well-known three shapes of nonlinear structures (sinusoidal, sawtooth, and spiky or bipolar) which are observed by numerous satellites and simulated by models in a Cartesian geometry, but also illustrate new results, such as, two reversely propagating nonlinear waves, density dips and humps, diverging and converging electric shocks, etc. A case study on Cluster satellite data is also introduced.

Observations of AGNs and microquasars by ASCA, RXTE, Chandra and XMM-Newton indicate the existence of broad X-ray emission lines of ionized heavy elements in their spectra. Such spectral lines were discovered also in X-ray spectra of neutron stars and X-ray afterglows of GRBs. Recently, Zakharov et al. (2003) described a procedure to estimate an upper limit of the magnetic fields in regions from which X-ray photons are emitted. The authors simulated typical profiles of the iron Kα line in the presence of magnetic field and compared them with observational data in the framework of the widely accepted accretion disk model. Here we further consider typical Zeeman splitting in the framework of a model of non-flat accretion flows, which is a generalization of previous consideration into non-equatorial plane motion of particles emitting X-ray photons. Using perspective facilities of space borne instruments (e.g. Constellation-X mission) a better resolution of the blue peak structure of iron Kα line will allow to evaluate the magnetic fields with higher accuracy.