1,721,023 research outputs found
Remote sensing of the magnetospheric plasma density by ULF waves recorded at a large array of magnetometer stations in Europe
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Long term changes in the plasmaspheric density through measurements of the ULF resonance frequency at low latitude
No full textInference of the magnetospheric plasma mass density from field line resonances: A test using a plasmasphere model
No full textUsing field-aligned ion density profiles from a physical-numerical model of the plasmasphere, we investigated the reliability of techniques which use field line resonance measurements to remotely sense the plasmaspheric mass density rho, over L=1.6-3.4. We find that the common assumption of some functional law for the variation of rho along different field lines may lead to distorted profiles of the equatorial density rho(o) as inferred from the observed fundamental field line eigenfrequency. The tests show that for midlatitude field lines (2.3<L<3.4) a radial power law with an index m congruent to 1 might be appropriate for a large variety of solar and geomagnetic conditions, and this index well represents the mass density dependence on the outer part of the field line. Indeed, an accurate integral expression of the field line eigenperiod demonstrates that the low-altitude plasma tube provides a negligible contribution to the eigenperiod. However, at lower latitudes, higher m values are necessary to obtain correct estimates of rho(o). In this case m represents only an average index, not related to any particular variation of rho along the field line. This effective index is also significantly dependent on solar activity conditions and local time. It turns out that inferred temporal variations of rho(o) at a given low L-shell can be significantly overestimated when a fixed functional dependence for the field-aligned mass density is assumed. The performance of more sophisticated techniques which use higher harmonics is also examined
Some theoretical aspects of the two-level magnetovariational method
No full textWe discuss some theoretical aspects of the two-level magnetovariational method for the determination of the underground electrical structure. The properties of two new apparent resistivity functions, respectively depending on gain and phase of the transfer function of the horizontal magnetic field variations between the Earth's surface and a given depth, are examined for two-layer Earth models. The effects of a finite wavelength of the source field are also investigated. It is shown that the measurement of the attenuation of the magnetic vertical component generated by an inhomogeneous source field can provide further information on the vertical distribution of the Earth's conductivity. In particular, it is shown that the measurement of the transfer function of both vertical and horizontal components between two levels can be used to estimate the average conductivity of the interlying medium
Un confronto fra misure di pulsazioni geomagnetiche effettuate simultaneamente in superficie ed in profondità nel laboratorio del Gran Sasso
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Remote sensing of the magnetospheric plasma mass density by ULF field line resonances: Effects of using different magnetic field models
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