An analytic approach to toroidal eigen mode

Sinha, A. K.; Rajaram, R. Κ.

doi:10.1029/97ja01039

Cited by 14 publications

(40 citation statements)

References 10 publications

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“…The phase shift of the azimuthal magnetic components between the two spacecraft was 180 • , whereas the radial electric components were in phase. Numerically solving the decoupled first-order wave equation along a dipole magnetic field line as derived in Sinha and Rajaram (1997) yields solutions for the magnetic and electric field. The following observations are qualitative and are only concerned with the node structure of the oscillation.…”

Section: Harmonic Structurementioning

confidence: 99%

Multi-instrument observations of a large scale Pc4 pulsation

et al. 2008

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Abstract. On 7 November 2005 various ground based and spaced based instruments registered five wave packets with frequencies in the Pc4 range. The most prominent of the five wave packets was observed in ground based magnetometer data spanning almost all latitudes on the dayside magnetosphere. The propagation from the dayside into the tail is deduced from Poynting flux calculations of Cluster data and an onset time analysis of the ground based magnetometer data. This suggests an upstream source. Backstreaming ions are identified to be the most probable source mechanism for this event. Due to the fortunate configuration of the Cluster satellites, the harmonic structure of the wave is analysed and compared with cross-phase spectra from ground data. We present evidence that the driving wave resonantly interacted with geomagnetic field lines. The data suggests that resonant driving occurred at stations where the driving frequency was harmonically related to the local fundamental frequency, creating FLR-like signatures.

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Section: Harmonic Structurementioning

confidence: 99%

Multi-instrument observations of a large scale Pc4 pulsation

et al. 2008

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“…analytic solution for the variation of the magnetic field perturbation along the dipolar field lines presented in Sinha and Rajaram (1997) indicates that the Cluster spacecraft are indeed expected to be far from magnetic field antinodes for the first two harmonics, and this may explain the dominance of the third harmonic at this time. Some departure from the predicted value could be due to the fact the Cummings et al (1969) model was based on the assumption of dipole magnetic field and realistically the field is slightly non-dipolar in nature, as illustrated by the model field presented in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…A number of theoretical estimates of field line eigenperiods are available at middle and high latitudes where hydrogen is dominant plasma component (e.g. Cummings et al, 1969;Sinha and Rajaram, 1997) as well as at low and equatorial latitudes where heavier species such as oxygen and helium take over (e.g. Poulter et al, 1988;Sinha et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Evidence of transverse magnetospheric field line oscillations as observed from Cluster and ground magnetometers

et al. 2005

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Abstract. The dynamic spectrum of ULF waves from magnetic field data obtained by the elliptically orbiting Cluster satellites (with an apogee of 119 000 km, perigee of 19 000 km and the orbital period of 57 h) have been prepared in the frequency range 0 to 120 mHz when the satellite was near its perigee. The existence of field line oscillations, with increasing frequency in the inbound sector and decreasing frequency in the outbound sector, is seen in the transverse components, indicating the presence of independently oscillating local magnetic flux tubes in the form of transverse standing Alfvén waves. The results show that toroidal and poloidal modes are excited simultaneously. The analysis of simultaneous ground magnetometer data at the footprint of the satellite suggests that these modes are also excited due to coupling to magnetospheric waveguide modes. The clear signature of a resonant fundamental mode is seen in the ground data whereas Cluster detects a harmonic of this frequency. Lower frequency modes indicative of waveguide oscillations are seen in both the ground data and the compressional field at Cluster.

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“…Theoretical estimates of field line eigen-periods are available (Cummings et al, 1969;Sinha and Rajaram, 1997). How-ever, most of such estimates are based on a suitably chosen density profile as a power law r −m for the hydrogen plasma.…”

Section: Theoretical Estimates Of Toroidal Eigen Periodsmentioning

confidence: 99%

“…The concept has thereafter taken deep roots and there are many ground-based and satellite observations that have established the relevance of field line oscillations (Cummings et al, 1969;Anderson et al, 1990). A number of theoretical estimates of field line eigen-periods are available (Cummings et al, 1969;Sinha and Rajaram, 1997), but most of these are valid for middle and high-latitude regions. The estimates of Poulter et al (1988) are more relevant to lowand equatorial-latitudes.…”

Section: Introductionmentioning

confidence: 99%

Low frequency modulation of transionospheric radio wave amplitude at low-latitudes: possible role of field line oscillations

et al. 2002

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Abstract. Ionospheric scintillations of radio waves at lowlatitudes are associated with electron density irregularities. These irregularities are field-aligned and can provide excitation energy all along the field line to non-local field-aligned oscillations, such as the local field line oscillations. Eigenperiods of toroidal field line oscillations at low-latitudes, computed by using the dipole magnetic field and ion distributions obtained from the International Reference Ionosphere (IRI) for typical nighttime conditions, fall in the range of 20-25 s. When subjected to spectral analysis, signal strength of the radio waves recorded on the 250 MHz beacon at Pondicherry (4.5 • N dip), Mumbai (13.4 • N dip) and Ujjain (18.6 • N dip) exhibit periodicities in the same range. For the single event for which simultaneous ground magnetic data were available, the geomagnetic field also oscillated at the same periodicity. The systematic presence of a significant peak in the 20-25 s range during periods of strong radio wave scintillations, and its absence otherwise suggests the possibility that field line oscillations are endogenously excited by the irregularities, and the oscillations associated with the excited field line generate the modulation characteristics of the radio waves received on the ground. The frequency of modulation is found to be much lower than the characteristic frequencies that define the main body of scintillations, and they probably correspond to scales that are much larger than the typical Fresnel scale. It is possible that the refractive mechanism associated with larger scale long-lived irregularities could be responsible for the observed phenomenon. Results of a preliminary numerical experiment that uses a sinusoidal phase irregularity in the ionosphere as a refracting media are presented. The results show that phase variations which are large enough to produce a focal plane close to the ground can reproduce features that are not inconsistent with our observations.

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An analytic approach to toroidal eigen mode

Cited by 14 publications

References 10 publications

Multi-instrument observations of a large scale Pc4 pulsation

Multi-instrument observations of a large scale Pc4 pulsation

Evidence of transverse magnetospheric field line oscillations as observed from Cluster and ground magnetometers

Low frequency modulation of transionospheric radio wave amplitude at low-latitudes: possible role of field line oscillations

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