Robert L. Lysak, Associate Fellow

Numerical Investigations of Solar Wind-Magnetosphere-Ionosphere Coupling

The work performed by these researchers was centered on several problems involving the coupling of mass, momentum, and energy between the solar wind, magnetosphere, and ionosphere. This work involved both the development of new codes and the modification and use of existing codes to address the problem of solar wind-magnetosphere-ionosphere coupling. The emphasis was on magnetosphere-ionosphere coupling during magnetospheric substorms. The following is a summary of specific projects.

These researchers extended their model for describing the dynamics of the turbulent convective flow in the magnetospheric boundary layer using the three-dimensional version of the total variance diminishing magnetohydrodynamic (MHD) code provided by the group lead by Thomas W. Jones of the Astronomy Department. The main focus in this area was on an investigation of the nonlinear dynamics of the magnetospheric tail using this code. In addition, the researchers continued their investigations of the Kelvin-Helmholtz instability and the excitation of field line resonances.

Additionally, the researchers applied their three-dimensional model for the propagation of compressional and shear Alfvén waves through the auroral ionosphere and atmosphere by looking at the excitation and propagation of waves progagating in the so-called ionospheric waveguide, and by looking at the detailed structure of the ionosphere including collisional effects. Having made the first steps in modifying the nonlinear MHD code described above to model the low-ß plasma in the auroral acceleration region. The researchers also included the effects of neutral winds in their calculations.

Another aspect of their research concerned modeling wave progagation in the inner magnetosphere and coupling these processes to those in the geomagnetic tail and at the magnetopause. This effort helped to describe the timing of magnetospheric phenomena during substorms as well as the propagation of the socalled Pi2 pulsations associated with substorms.

Lastly, the researchers performed particlein- cell numerical simulations to describe the nonlinear evolution of so-called ion and electron holes that have been recently observed by the National Aeronautics and Space Administration (NASA) Fast Auroral Snapshot (FAST) satellite. These phase space structures had previously been described theoretically in the steady state, but the evolution of such structures remains an open question. By implementing an Adaptive Mesh Refinement technique, the researchers hoped to more efficiently simulate these structures.

Specific projects, based on the implementation of the above research profile, included the MHD simulation of magnetospheric waveguide modes. Ultralow frequency waves with frequencies of 1.3, 1.9, 2.6, and 3.4 mHz are often observed and associated with field line resonances (FLRs) in the inner magnetosphere of the Earth. Waveguide modes were proposed as a mechanism for generating FLRs. Using a compressible two-dimensional MHD simulation, the researchers explored the nonlinear effects on the excitation of waveguide modes and frequencies of the modes. Changes in key parameters and how they affect waveguide modes were analyzed.

Another project developed by this group produced a three-dimensional model for the propagation of Alfvén waves through the auroral ionosphere. The propagation of Alfvén waves in the auroral ionosphere is important in the determination of ground signatures of timevarying currents, in the formation of Pc1 compressional waves that can be ducted in the ionosphere waveguide, and in the development of field-aligned currents and parallel electric fields during auroral acceleration processes. This research presented the first results from a three-dimensional model of the linear propagation of these waves. In this model, the ionosphere was treated as a thin slab carrying Pedersen and Hall currents. The jump conditions across this boundary lead to the coupling of shear and compressional MHD modes at the ionosphere and also allowed the ground signatures of these waves to be calculated within the context of the model. This model was used to study the coupling and to illustrate the excitation and propagation of compressional MHD waves within the ionospheric waveguide. A new numerical scheme for the modeling of parallel electric fields was also introduced and the excitation of resonance cone structures by narrow impulses was then demonstrated.

These researchers also performed studies of ion solitary waves using simulations including hydrogen and oxygen beams. Particle in cell simulations of solitary waves have been performed using a 2D3V code with one electron and two ion species. Data from the FAST and Polar spacecraft are used to provide input parameters, and based on the observations no cold plasma was included in contrast to earlier simulations. Simulations containing both oxygen and hydrogen beams were compared to simulations that contain only hydrogen to examine the effects of the oxygen on the behavior of the solitary waves. In both cases, the solitary wave speeds are less than the hydrogen beam speed, and they are also greater than the oxygen beam speed for the cases including oxygen. The simulated solitary waves have spatial scales on the order of 10λD. These speeds and scale sizes are consistent with Polar spacecraft observations in the low altitude auroral zone.

Research Group

Rachelle Bergmann, Department of Physics, Eastern Illinois University, Charleston, Illinois
James P. Crumley, Graduate Student Researcher
Kristi Keller, Laboratory for Extraterrestrial Physics, Goddard Space Flight Center, Greenbelt, Maryland
Dong-Hun Lee, Department of Astronomy and Space Science, Kyung Hee University, Seoul, Korea
Yan Song, Research Associate