Parametric Investigations of ULF Structure in
Global MHD Simulations of the Magnetosphere
Ultra Low Frequency waves, electric and magnetic variations at mHz time scales,
play an important role in the transport and energization of radiation belt
particles in the magnetosphere. However, not all sources and types of ULF
energy in the magnetosphere may effectively contribute to trapped particle
dynamics. For example, mode structure, propagation direction, and azimuthal
occurrence of ULF waves are all important contributing factors in determining
the degree to which a given source of ULF waves will affect magnetospheric
particles. However, these factors may depend on elements of the evolving
instantaneous state of the global magnetosphere, which may not be easy or even
possible to extract from the few scattered measurements typically available at
a given time via in situ observations.
Event studies have shown that the spatiotemporal structure and generation of
these waves is well suited to study by global-scale magnetospheric simulations.
While event studies provide an important validation of the approach, the
complicated structure of real solar wind observations make it very challenging
to isolate the physical factors controlling the generation of magnetospheric
ULF waves. In this study, we propose to use
global, 3d MHD simulations of the magnetosphere driven by idealized solar wind
conditions to parametrically study the effects of external driving of ULF waves
within the magnetosphere. This study will isolate the most important
conditions, including solar wind velocity, dynamic pressure, interplanetary
magnetic field strength, and solar wind electric field in determining the
occurrence, spatial, and spectral characteristics of magnetospheric ULF waves.
Results from these studies will be used to determine the controlling factors in
solar wind and magnetospheric configuration that lead to the geoeffective
generation of ULF power.
Understanding the relevant conditions and factors pertaining to the
transmission of energy from the solar wind to the radiation belts will be of
vital importance to understanding the environmental conditions to which human
technologies will be subject in the space surrounding Earth. The results of
this study will be relevant to the NASA strategic goal to Explore the Sun-Earth system to understand the Sun and its effects
on Earth, the solar system, and the space environmental conditions that will be
experienced by human explorers, and demonstrate technologies that can improve
future operational systems.
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