Ultra-low frequency (ULF) waves play an important role in a variety of phenomena that affect the magnetosphere of the Earth. In particular, the waves are coupled to processes that affect the relativistic electrons in the radiation belts.
This project will apply a superposed-epoch analysis to determine the statistical distribution of ULF wave power spectral density in the magnetosphere as a function of magnetic local time and the distance from the Earth. The wave power will be determined from ground-based measurements using arrays of magnetometers. The analysis will determine the wave growth and decay and will look specifically for the response of the ULF wave power to phenomena such as impacts of cornal mass ejections (CMEs) on the magnetosphere, high-speed solar wind streams, and ULF waves in the solar wind. The analysis will include various forms of filtering and nonlinear time-series analysis. The last part of the project will be to run magnetohydrodynamic (MHD) simulations to compare the ULF response from the simulations with what was determined from the data analysis.
The research will include graduate and undergraduate students. The work has societal benefits because of the relevance of the work to space weather phenomena.
Magnetospheric (space) research in this project was focused on first, growth and decay of ultra-low-frequency (ULF) plasma waves in Earth’s magnetosphere; and on the spatial distribution and spectral dependence of these processes; and second, the effects of these waves in scattering and energizing particles in the space environment, specifically the high-energy electrons that make up Earth's complex and interesting radiation belts. This research was mostly based on computer simulations of the waves and the electrons, and comparison with several magnetic storm events that were recorded by multiple spacecraft by NASA and other agencies. The research showed that waves are generated in very specific regions of the Earth's space environment (the magnetosphere) from which they spread out, and that they are mainly due to activity in the solar wind, the fast plasma flow from the Earth's surface, which gives the magnetosphere a teardrop shape (Fig. 1) and provides it with energy. A graduate student completed his Ph.D. thesis on modeling how such waves energize the electrons and how they carve out characteristic "island" patterns in the electron's location and velocity (Fig. 2). He showed how, when many waves are simultaneously present, the island structures disappear and electrons move much more erratically, or "diffuse" in different ways than what was known before. During magnetic storms, these small-scale motions of the electrons are translated into large-scale patterns that contribute to Earth's radiation belts and can persist for several days, potentially damaging spacecraft through "space weather" effects. Nonlinear models can reproduce these electron storms much better than linear models can (Fig. 3). Additional details of how specific types of waves are produced and how long they can have an impact on the electrons is shown in observations from NASA and NOAA spacecraft (Fig. 4). Numerical models are used to represent these wave effects so that we can understand how they come about. Parallel to research activities, a number of educational and outreach projects were developed in this ARRA-funded project. A graduate course in space physics was developed along with a two-semester "senior-design" course on space science lab for STEM undergraduates. In the latter, students designed, built, and tested a series of space experiments (a "payload") before traveling to NASA's Wallops Flight Facility in Virginia and launching it (Figs. 5-6). The two-stage rocket reaches 125-130 km before returning to Earth. This annual project, the course, and related outreach activity have inspired other colleges and organizations in the West Virginia/Western Maryland region to coordinate new space-related activities.
