Field line resonances in discretized magnetospheric models: an artifact study

Stellmacher, Martin; Glaßmeier, Karl‐Heinz; Lysak, R. L.; Kivelson, M. G.

doi:10.1007/s00585-997-0614-0

Cited by 5 publications

(2 citation statements)

References 45 publications

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“…Finally, we note that there are roughly six grid cells across the FWHM in these LFM simulations. If the FLRs are not fully resolved in the radial direction, there can be an unphysical leakage of wave energy from the FLR into the fast compressional mode [ Stellmacher et al , 1997]. Thus, the rapid decay of the FLRs in these simulations may not be entirely due to numerical dissipation.…”

Section: Discussionmentioning

confidence: 99%

Solar wind driving of magnetospheric ULF waves: Field line resonances driven by dynamic pressure fluctuations

et al. 2010

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[1] Several observational studies suggest that solar wind dynamic pressure fluctuations can drive magnetospheric ultralow-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.

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Section: Discussionmentioning

confidence: 99%

Solar wind driving of magnetospheric ULF waves: Field line resonances driven by dynamic pressure fluctuations

et al. 2010

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“…Claudepierre et al [2010] were the first to show in the self-consistent, global MHD Lyon-Fedder-Mobarry model (LFM) that fluctuations in the upstream dynamic pressure can produce FLRs in the dayside magnetosphere and to show that they were driven by cavity modes. Even then, others argue that the discretization of Cartesian grids, such as in the SWMF model, and the Alfvén continuum dampen and obscure what is otherwise a localized resonance phenomena, which make them difficult to detect, particularly with broadband sources, or difficult to produce altogether [Stellmacher et al, 1997]. Bellan [1996], for instance, showed that kinetic Alfvén waves mediate the coupling between fast and shear modes, which may suggest FLRs in MHD models are an unphysical, numerical artifact.…”

Section: Introductionmentioning

confidence: 99%

Local time asymmetries and toroidal field line resonances: Global magnetospheric modeling in SWMF

2016

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We present evidence of resonant wave‐wave coupling via toroidal field line resonance (FLR) signatures in the Space Weather Modeling Framework's (SWMF) global, terrestrial magnetospheric model in one simulation driven by a synthetic upstream solar wind with embedded broadband dynamic pressure fluctuations. Using in situ, stationary point measurements of the radial electric field along the 1500 LT meridian, we show that SWMF reproduces a multiharmonic, continuous distribution of FLRs exemplified by 180° phase reversals and amplitude peaks across the resonant L shells. By linearly increasing the amplitude of the dynamic pressure fluctuations in time, we observe a commensurate increase in the amplitude of the radial electric and azimuthal magnetic field fluctuations, which is consistent with the solar wind driver being the dominant source of the fast mode energy. While we find no discernible local time changes in the FLR frequencies despite large‐scale, monotonic variations in the dayside equatorial mass density, in selectively sampling resonant points and examining spectral resonance widths, we observe significant radial, harmonic, and time‐dependent local time asymmetries in the radial electric field amplitudes. A weak but persistent local time asymmetry exists in measures of the estimated coupling efficiency between the fast mode and toroidal wave fields, which exhibits a radial dependence consistent with the coupling strength examined by Mann et al. (1999) and Zhu and Kivelson (1988). We discuss internal structural mechanisms and additional external energy sources that may account for these asymmetries as we find that local time variations in the strength of the compressional driver are not the predominant source of the FLR amplitude asymmetries. These include resonant mode coupling of observed Kelvin‐Helmholtz surface wave generated Pc5 band ultralow frequency pulsations, local time differences in local ionospheric dampening rates, and variations in azimuthal mode number, which may impact the partitioning of spectral energy between the toroidal and poloidal wave modes.

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Spatiotemporal characteristics of cusp latitude spectra

Szuberla¹,

Olson²,

Engebretson³

et al. 2000

J. Geophys. Res.

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Abstract. In this study we analyze the spatiotemporal characteristics of spectra generated from 754 days of cusp latitude magnetometer data (Longyearbyen and selected Magnetometer Array for Cusp and Cleft Studies (MACCS) stations). In order to distinguish between the presence of spatial (fixed in magnetic local time) and temporal (fixed in universal time) signatures in cusp latitude spectra we develop a simple test using trace power, polarization, and ellipticity spectra. On the basis of this test we find evidence for both spatial and temporal signatures in cusp latitude spectra. We find that the trace power spectrum is dominated by temporal information; however, the polarization and ellipticity spectra contain unambiguous spatial structure. Temporal information in cusp latitude spectra is carried primarily by broadband Pc3 (10-50 mHz) noise, while spatial information is carried by polarized Pc5 (1-10 mHz) pulsations. Additionally, we establish a state-space measure as a quantitative means of discriminating the spatial passage of the cusp and boundary regions by ground-based magnetic means. The measure is based on the difference between daily polarization spectra (centered on local magnetic noon) and the mean polarization spectra for a given station. This procedure replaces previous determinations which were made from spectra "by-eye." The MACCS array is operated by Mark Engebret-

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Field line resonances in discretized magnetospheric models: an artifact study

Cited by 5 publications

References 45 publications

Solar wind driving of magnetospheric ULF waves: Field line resonances driven by dynamic pressure fluctuations

Solar wind driving of magnetospheric ULF waves: Field line resonances driven by dynamic pressure fluctuations

Local time asymmetries and toroidal field line resonances: Global magnetospheric modeling in SWMF

Spatiotemporal characteristics of cusp latitude spectra

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