Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm33a1751c&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM33A-1751
Other
2730 Magnetosphere: Inner, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2774 Radiation Belts, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Magnetospheric ultra-low frequency (ULF) waves play an important role in the dynamics of radiation belt electron populations, enhancing rates of particle transport due to radial diffusion. There is increasing evidence that magnetospheric ULF waves relevant to radiation belt dynamics are ultimately driven by the solar wind. Thus, determining the solar wind parameters that are the most effective in generating magnetospheric ULF waves is an important question for radiation belt physics. Several observational studies suggest that fluctuations in the solar wind dynamic pressure can directly drive dayside magnetospheric ULF waves. To better understand this causal relationship, we present initial results from Lyon-Fedder-Mobarry (LFM) global, three-dimensional MHD simulations of the solar wind-magnetosphere interaction. These simulations are driven with idealized solar wind input conditions, where we introduce monochromatic and broadband ULF fluctuations in the upstream solar wind dynamic pressure. These 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 present a limited set of results from five LFM simulations: four driven by monochromatic upstream dynamic pressure fluctuations and one by quasi- broadband upstream dynamic pressure fluctuations. We show that these upstream solar wind dynamic pressure fluctuations directly drive dayside magnetospheric ULF pulsations, in a manner similar to that suggested by Kepko and Spence [2003] and others. Moreover, we show that when the frequency of the upstream dynamic pressure fluctuations matches one of the natural frequencies of the magnetosphere, magnetospheric cavity modes are excited near the noon meridian. Our simulations also suggest that only even-mode number cavity oscillations are possible within the dayside magnetosphere. We compute the frequency, azimuthal mode number and power spectral densities of these dynamic pressure-driven ULF waves/cavity modes. This allows us to quantify the effect that these waves could have on radiation belt electrons, via ULF enhanced radial diffusion. We find that these dynamic pressure driven ULF waves could effectively interact with radiation belt electrons ranging from a few keV to energies in excess of 1 MeV.
Claudepierre Seth G.
Elkington Scot R.
Wiltberger Michael
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