Maha Ashour-Abdalla - US grants

One of the critical regions of the magnetosphere is the magnetotail, which is thought to be responsible for magnetospheric substorms, which are intervals of time that are associated with enhanced currents and intensification of the auroral (i.e. northern lights). This grant concentrates on three problems concerning the plasma physics of the magnetotail: 1) the origin of mid-frequency electrostatic plasma waves, 2) collisionless tearing mode reconnection in teh closed magnetic field-line region of the plasma sheet, and 3) the structure of collisionless shocks in the distant tail. These problems will be attached using observations, analytic theory and numerical simulations.

A workshop on the magnetopause and boundary layer physics is planned for the definition phase of the GEM program. This workshop will bring together theoreticians and experimentalists to review their knowledge of boundary layer physics and to recommend the future direction of research. Small working groups will be formed to define the theory campaign and its interaction with observational research. The research topics of this workshop are important in understanding microscale processes in the solar wind-magnetosphere-ionosphere-mesosphere coupling on a global scale.

An integral component of the multi-agency U.S. Global Change Research Program (Our Changing Planet," Committee on Earth Sciences, 1991) is understanding and modeling the geospace environment. As part of its contribution to the U.S. Global Change Research Program, the National Science Foundation's Division of Atmospheric Sciences has established a new research initiative, Geospace Environment Modeling (GEM), with the goal of supporting basic research into the dynamical and structural properties of geospace, leading to the construction of a global geospace model with predictive capability. The subjects of the first GEM campaign are the magnetospheric boundary, the magnetosheath beyond it, and the connection from the boundary through the magnetosphere to the ionosphere. This grant is for support to model electron and ion distribution functions near and within the dayside magnetopause in order to identify key particle signatures of the magnetopause electric and magnetic fields. The codes prepared for this project will be made available for inclusion into the GEM program's Global Circulation Model.

The International School for Space Simulations (ISSS) was originally conceived as a means of bringing together established and beginning investigators in space plasma physics. A broader scope was to increase communication in order to advance the use of space plasma simulations by the scientific community as a whole. This grant is for support of ISSS-4 which will be held March 25 - April 6, 1991 in both Kyoto and Nara Japan. The conference will consist of two distinct segments. The first week will be devoted to lectures and exercises on simulation techniques and will take place in Kyoto. The second segment will be held in Nara and consist of a symposium for the presentation and discussion of recent research topics and methods related to simulations (e.g. observations, data analysis, model development).

9312467 Ashour-Abdalla The proposed theoretical investigation is to calculate electron distributions in the geomagnetic tail to the Earth's magnetosphere and to evaluate the local and global problem of charge neutrality between electrons and ions. Although the dynamics of ions in the magnetotail has been the subject of extensive theoretical investigations using single particle orbit calculations, hybrid simulations, and magnetohydrodynamic fluid simulations, electron dynamics have been virtually ignored. Yet, the most fundamental aspect of a plasma - the establishment and maintenance of charge neutrality - depends on electron behavior. Some electrons move at high speeds and rapidly traverse large volumes of space; the establishment of local charge neutrality depends on both the global sources and sinks of electrons and the large scale structure of the electric and magnetic fields in the tail. Until now, no scientific methodology has existed capable of addressing global transport and calculating the local distributions of electrons in the tail. In the proposed large scale kinetics approach, starting from various source regions, electrons will be allowed to propagate throughout the entire volume of the magnetotail along trajectories which are determined using model electromagnetic fields to represent the tail configuration. The local electron distribution function will be calculated by summing the contributions of each trajectory passing through the local spatial region, and the electron density will be compared to the local ion density (which is similarly calculated by the large scale kinetics technique) to determine the extent of charge neutrality violation. Parallel electric fields will be added to the electromagnetic field model, and will be adjusted to obtain the closet reasonable balance between electron and ion charge densities. The potential significance of this proposed is profound in that, with its success we could for the first time directly asses s the problem of charge neutrality in a space plasma, determine the large scale potential electric fields required to maintain charge neutrality, and establish the extent to which charge neutrality demands the exchange of electrons between the tail plasma and the ionosphere. ***

This proposal outlines a study of the formation of auroral arcs caused by the large scale dynamics of ions and electrons in the magnetotail. The first step is to construct ion distribution functions moments (density, temperature, pressure, etc.) in a three-dimensional large scale magnetospheric model. This will be done using the technique of large scale kinetics, whereby thousands of ion trajectories are launched from a variety of sources into a magnetic and electric field model of the magnetosphere. The 3D auroral precipitation profile (with local time dependence) will be determined and compared with observations. The second step will be to perform a similar large scale kinetic study using electrons, after which the ion and electron results will be compared and in regions where there are charge imbalances, parallel electric fields will be imposed. The precipitated electron flux will then be calculated and theoretical auroral images will be produced. The third step is to introduce time dependence into the large scale kinetic model. This will be done by using different field model "snapshots" which represent different states (i.e., growth phase, recovery, etc.) of the magnetosphere and calculating the ion and electron precipitation profiles. Once a general understanding using these snapshots has been achieved, an attempt will be made to model the growth phase by temporally evolving the quiet time field model to a more disturbed time. The last step is to bring all of these results together to delineate the formation of auroral arcs. The physical mechanisms in the magnetotail that result in the large longitudinal extent of auroral arcs will be identified and the results will be compared to observations.

This program will utilize a combination of two computational techniques to investigate the penetration of high energy particles from the solar wind into the Earth's magnetosphere. Magnetohydrodynamic (MHD) simulations will be used to determine the general interior structure and dynamics of the magnetosphere and a large-scale kinetic (LSK) code will be used to trace test particles to determine where, how, and when energetic particles penetrate the magnetopause and enter the magnetosphere. Particle tracing will then also be used to determine how these energetic particles are transported within the magnetosphere

This project will utilize magnetohydrodynamic (MHD) simulations of the magnetosphere-ionosphere system to examine the sensitivity of MHD simulations to variability of the solar wind driver. The work will compare the variability induced by intrinsic, internal magnetospheric dynamics with the variability caused by both temporal and spatial variability in the solar wind. Case studies will be done with real events to allow for comparisons of the simulations with realistic conditions. This work will provide a mechanism for determining the accuracy with which MHD models might in the future be able to predict space weather conditions.

The dynamics of the space environment near Earth is driven by the interaction between the solar wind and the Earth's magnetic field. A characteristic feature on the nightside of Earth is a cyclic storage and explosive release of energy in the magnetic field. The detailed understanding of how magnetic energy is converted into heating and large-scale transport of the plasma in this process still eludes us. One outstanding question concerns the acceleration of electrons to very high energies. Observations show that this happens on a much larger scale than can easily be explained by the small-scale physical processes involved. Recent studies have confirmed the large-scale dynamics of the nightside region during these events as the dominant source for the energization. Entangling the complex mix of processes over a wide range of scales for a comprehensive, quantitative description of the generation and evolution of the energetic electrons is an important current challenge in magnetospheric physics. This project will utilize a combination of advanced computer codes to simulate the effects on the particles of both the small- and large-scale processes involved. Simulation results from three real-life events observed by spacecraft will be analyzed and compared to determine where and how electrons are accelerated during these events. The novel multi-scale approach the team will employ promises to provide the first quantitative assessment of the relative roles of the various processes. It will also provide crucial new insights into the importance of cross-scale coupling. The magnetic energy conversion process that is the subject of this study is a generic plasma physics process that operates in a wide range of space and laboratory plasmas. The Earth's magnetosphere is a natural laboratory for studying such processes, where both simulations and direct observations are possible. Results from this project therefore will impact a broad variety of research areas.

When the electrons with great energy are propelled back toward Earth, they can impact the near-Earth space environment. Some are trapped in the stronger magnetic field there and contribute to the make-up of the Earth radiation belts. Others precipitate into the upper atmosphere where the impact contributes to the creation, amongst others, of strong auroral displays. The disturbance effects in the space environment near Earth are of concern for satellites and other technological systems on the Earth surface that might be affected. This adds broad societal relevance and importance to the research study. The project will integrate research and education through the training of a graduate student. The graduate student will work with members of the team to complement his thesis work on multi-scale processes. In addition, a number of undergraduate interns will participate in the project during the summers. Finally, the PI is a founder and member of the program committee for the International School for Space Simulations (ISSS). This school focuses on student learning of simulation techniques. The PI will continue her active involvement with this activity as part of this project.

This is a numerical modeling project focused on the magnetotail. Its goal is to determine where and how electrons are accelerated during magnetospheric substorms. The aim is to understand the multi-scale nature of the acceleration process by including the effects of kinetic processes that occur near the neutral line while taking into account the global changes in the configuration of the magnetotail. In particular, the study will quantify the relative role of reconnection and dipolarization fronts in energizing electrons during substorm events. Previous investigations of the acceleration of electrons associated with dipolarization fronts have been carried out using either local particle-in-cell (PIC) simulations or large-scale kinetic calculations based on following large numbers of electrons in the time dependent electric and magnetic fields obtained from global Magneto-Hydro-Dynamic (MHD) simulations. Here, a multi-scale approach will be adopted that incorporates the effects of kinetic processes, including wave-particle interactions that occur near the neutral line, while taking into account the global changes in the configuration of the magnetotail. The results of global MHD simulations will be used to determine the initial and boundary conditions of a three-dimensional particle in cell simulation by setting the magnetic fields and particle flows at the boundaries to the values given by the MHD results. The simulation system will include the region of fast outflow emanating from the reconnection site that drives the formation of dipolarization fronts. The acceleration seen in the implicit-particle-in-cell code (iPIC3d) will be characterized in order to address the questions of electron energization near the reconnection site. Finally, large-scale kinetic simulations using the electric and magnetic fields from the MHD simulation will provide information on energization and precipitation loss as the dipolarization front moves earthward. The effects of adiabatic and non-adiabatic heating of the electrons will be compared and contrasted between several simulations to determine whether the predominant acceleration and heating mechanisms are different for various substorms and what causes that variation.