Modeling Ultra-Low Frequency (ULF) Waves in the Near-Earth Magnetosphere

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Ultra-low frequency (ULF) waves play a major role in the transport of energy in the near-Earth regions of the magnetosphere. This project research will further develop a magnetohydrodynamic (MHD) simulation for the study of ULF waves and will apply the code to several problems involving ULF waves in the magnetosphere. Pi1 and Pi2 waves, which have periods of 1-40 seconds and 40-150 seconds respectively, are frequently observed at the onset of magnetospheric substorms. Since these waves can be observed world-wide, their propagation from a source region to the ionosphere and to the ground requires further study. At longer periods, Pc3-5 waves (10-600 seconds) have been used as diagnostics of the mass distribution in the near-Earth regions of the magnetosphere. At the high end of the ULF range, Pc1 waves (0.2- 5 seconds) can interact with the cyclotron motion of ions in the magnetosphere and cause energization and pitch angle scattering in the inner magnetosphere. These waves can propagate long distances through the ionosphere in the so-called ionospheric waveguide. Development and application of a global ULF wave model that can investigate these interactions is the primary goal of this project. An important aspect of this modeling is to connect the waves as observed by spacecraft in orbit with waves observed on the ground with magnetometers and in the ionosphere with radar observations. The modeling of ULF waves will include the dynamics of Pi1 and Pi2 pulsations at substorm onset and their timing at both high and mid-latitudes with respect to driving sources in the magnetotail. The improved MHD simulation code will make it possible to understand both the transient propagation of ULF waves as well as the development of field line resonances, both of which can be used to diagnose the mass density of the magnetosphere. The extension of the model to include ion cyclotron effects will make it possible to study the propagation of electromagnetic ion cyclotron (EMIC) waves from their sources in the magnetosphere through the ionospheric waveguide. A significant part of the research will be carried out by graduate students, who will be trained in the art of scientific computation as well as the physics understanding necessary to interpret the results of not only the numerical results but also the data obtained by satellites, radars, and ground magnetometers. In addition, the work will also produce a ULF wave model for magnetosphere-ionosphere coupling that can be applied to many problems in magnetospheric physics.