On the coupling of fast and shear Alfvén wave modes by the ionospheric Hall conductance

Waters, C. L.; Lysak, R. L.; Sciffer, M. D.

doi:10.5047/eps.2012.08.002

Cited by 22 publications

(26 citation statements)

References 80 publications

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“…He showed that as compressional oscillations penetrate deep into the magnetosphere, their amplitude decreases several orders of magnitude. Recently, Waters et al (2013) reported that the Hall conductance in the ionosphere can couple shear Alfvén waves trapped in the Ionospheric Alfvén Resonator (IAR) to fast mode waves that propagate across the ambient magnetic field in an ionospheric waveguide. The coupled equation has not been solved, even in a dipole magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Toroidal quarter waves in the Earth’s magnetosphere: theoretical studies

Bulusu

Sinha

Vichare

2014

Astrophys Space Sci

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An analytic model has been developed for toroidal quarter wave (QW) oscillations in the Earth's magnetosphere using idealistic and highly asymmetric ionospheric boundary condition. The background magnetic field is dipolar and plasma density distribution is governed by a power law 1/r m where r is the geocentric distance of any point along the field line and m is the density index. The solution thus obtained has been compared with the numerical solutions. Earlier workers had developed the analytic model for trivial 1/r 6 (m = 6) type of plasma density distribution along the field line for which the period of the fundamental is twice that of corresponding half wave (i.e. toroidal oscillation in the symmetric ionospheric boundary). The present analytic model does reproduce this feature. In addition, it is seen that this ratio decreases for lower values of m. Moreover, for a particular value of m, this ratio shows a decreasing trend with increased harmonic number. The spatial characteristics of QW obtained from present analytic model are in excellent agreement with those computed numerically, thereby validating the model. The departure of frequency computed analytically from that obtained numerically is significant only for the fundamental and this departure reduces sharply with the increased harmonic number. It should be noted that there is no such departure for 1/r 6 type of plasma density distribution and spatial structures as well as frequency computed from the present analytic model match perfectly with those computed numerically.

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Section: Introductionmentioning

confidence: 99%

Toroidal quarter waves in the Earth’s magnetosphere: theoretical studies

Bulusu

Sinha

Vichare

2014

Astrophys Space Sci

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“…More specifically, we used the B Z, GSE magnetospheric component and the H ground component. At high and middle latitudes, their behavior should be comparable because of the 90 • rotation of the polarization axes through the ionosphere (Hughes and Southwood, 1974;Sciffer et al, 2005;Piersanti et al, 2012;Waters et al, 2013). During the entire period of interest, the K-index ranges between 0 and 1 (K being the 3 h long quasilogarithmic local index of geomagnetic activity for this observatory: http://roma2.rm.ingv.it/en/).…”

Section: Magnetospheric and Ground Observations: Emd Approachmentioning

confidence: 99%

Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations

et al. 2016

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Abstract. We used the empirical mode decomposition (EMD) to investigate the time variation of the magnetospheric and ground-based observations of the Earth's magnetic field during both quiet and disturbed periods. We found two timescale variations in magnetospheric data which are associated with different magnetospheric current systems and the characteristic diurnal orbital variation, respectively. On the ground we identified three timescale variations related to the solar-wind-magnetosphere high-frequency interactions, the ionospheric processes, and the internal dynamics of the magnetosphere. This approach is able to identify the different physical processes involved in solar-windmagnetosphere-ionosphere coupling. In addition, the largetimescale contribution can be used as a local index for the identification of the intensity of a geomagnetic storm on the ground.

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“…The fast mode, on the other hand, has a component along the ambient field and energy moves in the direction of the wave vector, which can make any angle with the ambient field. The background nonuniform magnetic field couples the two modes and has been discussed in different magnetic field geometries by different authors [ Lanzerotti and Southwood , ; Leonovich , ; Waters et al , ]. The coupled equation has not been solved in dipole magnetic field geometry.…”

Section: Introductionmentioning

confidence: 99%

An analytic model of toroidal half‐wave oscillations: Implication on plasma density estimates

2015

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The developed analytic model for toroidal oscillations under infinitely conducting ionosphere (“Rigid‐end”) has been extended to “Free‐end” case when the conjugate ionospheres are infinitely resistive. The present direct analytic model (DAM) is the only analytic model that provides the field line structures of electric and magnetic field oscillations associated with the “Free‐end” toroidal wave for generalized plasma distribution characterized by the power law ρ = ρo(ro/r)m, where m is the density index and r is the geocentric distance to the position of interest on the field line. This is important because different regions in the magnetosphere are characterized by different m. Significant improvement over standard WKB solution and an excellent agreement with the numerical exact solution (NES) affirms validity and advancement of DAM. In addition, we estimate the equatorial ion number density (assuming H+ atom as the only species) using DAM, NES, and standard WKB for Rigid‐end as well as Free‐end case and illustrate their respective implications in computing ion number density. It is seen that WKB method overestimates the equatorial ion density under Rigid‐end condition and underestimates the same under Free‐end condition. The density estimates through DAM are far more accurate than those computed through WKB. The earlier analytic estimates of ion number density were restricted to m = 6, whereas DAM can account for generalized m while reproducing the density for m = 6 as envisaged by earlier models.

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On the coupling of fast and shear Alfvén wave modes by the ionospheric Hall conductance

Cited by 22 publications

References 80 publications

Toroidal quarter waves in the Earth’s magnetosphere: theoretical studies

Toroidal quarter waves in the Earth’s magnetosphere: theoretical studies

Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations

An analytic model of toroidal half‐wave oscillations: Implication on plasma density estimates

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