Charge exchange avalanche at the cometopause

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95404/1/grl3768.pd

Modeling of nonequilibrium space plasma flows

Godunov-type numerical solution of the 20 moment plasma transport equations. One of the centerpieces of our proposal was the development of a higher order Godunov-type numerical scheme to solve the gyration dominated 20 moment transport equations. In the first step we explored some fundamental analytic properties of the 20 moment transport equations for a low b plasma, including the eigenvectors and eigenvalues of propagating disturbances. The eigenvalues correspond to wave speeds, while the eigenvectors characterize the transported physical quantities. In this paper we also explored the physically meaningful parameter range of the normalized heat flow components. In the second step a new Godunov scheme type numerical method was developed to solve the coupled set of 20 moment transport equations for a quasineutral single-ion plasma. The numerical method and the first results were presented at several national and international meetings and a paper describing the method has been published in the Journal of Computational Physics. To our knowledge this is the first numerical method which is capable of producing stable time-dependent solutions to the full 20 (or 16) moment set of transport equations, including the full heat flow equation. Previous attempts resulted in unstable (oscillating) solutions of the heat flow equations. Our group invested over two man-years into the development and implementation of the new method. The present model solves the 20 moment transport equations for an ion species and thermal electrons in 8 domain extending from a collision dominated to a collisionless region (200 km to 12,000 km). This model has been applied to study O+ acceleration due to Joule heating in the lower ionosphere

VEGA: En route to Venus and comet Halley

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95520/1/eost5312.pd

Particle acceleration at comets

This paper compares calculated and measured energy spectra of implanted H+ and O+ ions on the assumption that the pick‐up geometry is quasi‐parallel and about 1% of the waves generated by the cometary pickup process propagates backward (towards the comet). The model provides a good description of the implanted O+ and H+ energy distribution near the pickup energies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87298/2/267_1.pd

An analytic solution to the steady‐state double adiabatic equations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94665/1/grl5619.pd

Global Asymmetry of the Heliosphere

Opher et al. 2006 showed that an interstellar magnetic field parallel to the plane defined by the deflection of interstellar hydrogen atoms can produce a north/south asymmetry in the distortion of the solar wind termination shock. This distortion is consistent with Voyager 1 and Voyager 2 observations of the direction of field-aligned streaming of the termination shock particles upstream the shock. The model also indicates that such a distortion will result in a significant north/south asymmetry in the distance to the shock and the thickness of heliosheath. The two Voyager spacecraft should reveal the nature and degree of the asymmetry in the termination shock and heliosheath.Comment: 6 pages, 5 figures, AIP Proceedings of the 5th IGPP "The Physics of the Inner Heliosheath: Voyager Observations, Theory and Future Prospects

A Titov-D\'emoulin Type Eruptive Event Generator for β>0\beta>0 Plasmas

We provide exact analytical solutions for the magnetic field produced by prescribed current distributions located inside a toroidal filament of finite thickness. The solutions are expressed in terms of toroidal functions which are modifications of the Legendre functions. In application to the MHD equilibrium of a twisted toroidal current loop in the solar corona, the Grad-Shafranov equation is decomposed into an analytic solution describing an equilibrium configuration against the pinch-effect from its own current and an approximate solution for an external strapping field to balance the hoop force. Our solutions can be employed in numerical simulations of coronal mass ejections. When superimposed on the background solar coronal magnetic field, the excess magnetic energy of the twisted current loop configuration can be made unstable by applying flux cancellation to reduce the strapping field. Such loss of stability accompanied by the formation of an expanding flux rope is typical for the Titov & D\'emoulin (1999) eruptive event generator. The main new features of the proposed model are: (i) The filament is filled with finite $\beta$ plasma with finite mass and energy, (ii) The model describes an equilibrium solution that will spontaneously erupt due to magnetic reconnection of the strapping magnetic field arcade, and (iii) There are analytic expressions connecting the model parameters to the asymptotic velocity and total mass of the resulting CME, providing a way to connect the simulated CME properties to multipoint coronograph observations.Comment: 20 pages, 7 figure

Dusty cometary atmospheres

This paper summarizes our present understanding of the physical processes controlling the dust and gas production of cometary nuclei and the evolution of the dusty gas flow in the inner coma. Special emphasis is being made to compile a self-consistent set of governing equations describing the accelerating dusty gas flow in a cometary atmosphere.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26895/1/0000461.pd