  Several observational studies suggest that solar wind dynamic pressure
fluctuations can drive magnetospheric ultra-low frequency (ULF) waves on the
dayside. To investigate this causal relationship, we present results from
Lyon-Fedder-Mobarry (LFM) global, three-dimensional magnetohydrodynamic (MHD)
simulations of the solar wind-magnetosphere interaction. These simulations are
driven with synthetic solar wind input conditions, where idealized ULF dynamic
pressure fluctuations are embedded in the upstream solar wind. In three of the
simulations, a monochromatic, sinusoidal ULF oscillation is introduced into the
solar wind dynamic pressure time series. In the fourth simulation, a continuum
of ULF fluctuations over the 0-50 mHz frequency band is introduced into the
solar wind dynamic pressure time series. In this numerical experiment, the
idealized solar wind input conditions allow us to study only the effect of a
fluctuating solar wind dynamic pressure, while holding all of the other solar
wind driving parameters constant. We show that the monochromatic solar wind
dynamic pressure fluctuations drive toroidal mode field line resonances (FLRs)
on the dayside, at locations where the upstream driving frequency matches a
local field line eigenfrequency. In addition, we show that the continuum of
upstream solar wind dynamic pressure fluctuations drives a continuous spectrum
of toroidal mode FLRs on the dayside. The characteristics of the simulated FLRs
agree well with FLR observations, including a phase reversal radially across a
peak in wave power, a change in the sense of polarization across the noon
meridian, and a net flux of energy into the ionosphere.
