Whistler-mode wave-injection experiments in the plasmasphere with a radio sounder

Sonwalkar, V. S.; X, Chen; Harikumar, Jayashree; Carpenter, D. L.; Bell, T. F.

doi:10.1016/s1364-6826(00)00223-6

Cited by 13 publications

(15 citation statements)

References 57 publications

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“…On 30 September 2004, as a result of an unknown failure of the Y‐antenna/receiver system, the signal strength received by the Y‐antenna was reduced substantially. The loss of part of the X‐antenna and the unknown loss with respect to signal from the Y‐antenna has made it difficult to make wave‐normal direction measurements [ Sonwalkar et al , 2001, 2004b]. On the other hand, as discussed in the next section, the failure of the Y‐antenna/receiver system in September 2004 led to an unexpected benefit: it permitted detection of diffuse MR‐WM echoes which in a large number of instances could not be recognized on the X and Z antennas because of receiver saturation.…”

Section: Instrument Descriptionmentioning

confidence: 99%

Magnetospherically reflected, specularly reflected, and backscattered whistler mode radio-sounder echoes observed on the IMAGE satellite: 1. Observations and interpretation

et al. 2011

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[1] A survey of echoes detected in 2004-2005 during pulse transmissions from the Radio Plasma Imager (RPI) instrument on the IMAGE satellite has revealed several new features of sounder generated whistler mode (WM) echoes and has indicated ways in which the echoes may be used for remote sensing of the Earth's plasma structure at altitudes <5000 km. In this paper we describe the frequency versus travel time ( f − t) forms of the WM echoes as they appear on RPI plasmagrams and discuss qualitatively their raypaths and diagnostic potentials. Based on their reflection mechanism, the WM echoes can be classified as: magnetospherically reflected (MR), specularly reflected (SR), or backscattered (BS). The MR echoes are reflected at altitudes where the local lower hybrid frequency ( f lh ) is equal to the transmitted pulse frequency f, a phenomenon familiar from both theory and passive recordings of WM wave activity. The SR echoes (previously reported in a higher frequency range) are reflected at the Earth-ionosphere boundary, either with wave vector at normal incidence or, more commonly (and unexpectedly, due to ray bending in the layered ionosphere), at oblique incidence. The BS echoes are the result of scattering from small scale size plasma density irregularities close to IMAGE. The echoes are described as discrete, multipath, and diffuse, depending upon the amount of travel-time spreading caused by the presence of field aligned density irregularities (FAIs) along echo raypaths. The WM echoes described in this paper have been observed at altitudes less than 5,000 km and at all latitudes and at most MLTs. The diagnostic potential of these phenomena for remotely studying the distribution of plasma density and composition along the geomagnetic field line B 0 , as well as the presence of FAIs of varying scale sizes, is enhanced by the tendency for SR and MR echoes to be observed simultaneously along with the upward propagating signals from a spatial distribution of communication VLF transmitters. We believe that our findings about WM propagation and echoing in an irregular medium have important implications for the connection between WM waves and the Earth's radiation belts. In a companion paper by Sonwalkar et al. (2011), we employ ray tracing and refractive index diagrams in quantitative support of this paper and also present two diagnostic case studies of plasma density, ion effective mass, and ion composition along B 0 .Citation: Sonwalkar, V. S., D. L. Carpenter, A. Reddy, R. Proddaturi, S. Hazra, K. Mayank, and B. W. Reinisch (2011), Magnetospherically reflected, specularly reflected, and backscattered whistler mode radio-sounder echoes observed on the IMAGE satellite: 1. Observations and interpretation,

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Section: Instrument Descriptionmentioning

confidence: 99%

Magnetospherically reflected, specularly reflected, and backscattered whistler mode radio-sounder echoes observed on the IMAGE satellite: 1. Observations and interpretation

et al. 2011

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“…Lacking such a remote receiver, RPI has been forced to depend upon the special conditions under which whistler mode echoes of its signals can be received. Three such conditions are envisaged [ Sonwalkar et al , 2001]. In the magnetospheric reflection, or MR, process, the direction of a downgoing ray is reversed when the wave frequency becomes equal to the local value of the lower hybrid resonance frequency f lh .…”

Section: Observations Of Whistler Mode Echoesmentioning

confidence: 99%

“…To explain the time delay spreading, we consider the subset of injected waves with wave normals from 0° to within ≈2° of the resonance cone. These waves propagate downward with group velocities not far below a maximum value associated with propagation exactly along B (this is a reasonable assumption because for f ≪ f ce , most of the radiation is expected to be confined to a lobe in the direction of the magnetic field [ Sonwalkar et al , 2001]). At some altitude, or range of altitudes, the waves encounter field‐aligned irregularities that are spread in latitude (and longitude).…”

Section: Ray‐tracing Interpretation Of Observed Whistler and Accompanmentioning

confidence: 99%

“…Once IMAGE moved into the development phases, its broad potential for whistler mode probing became clear. It was pointed out that in major parts of the plasmasphere the whistler mode refractive index is high, of order 10, and the long RPI antennas are approximately a half wavelength in extent and can have a radiation efficiency at whistler mode frequencies of as much as 10% [e.g., Sonwalkar et al , 2001], much higher than when, usually at much higher altitudes, radiation at those same frequencies is in the free space modes. In the latter case, the efficiency of the antennas drops steeply with decreasing frequency below 100 kHz from a maximum near 200–300 kHz [ Reinisch et al , 2000].…”

Section: Introductionmentioning

confidence: 99%

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Diagnostics of magnetospheric electron density and irregularities at altitudes <5000 km using whistler and Z mode echoes from radio sounding on the IMAGE satellite

et al. 2004

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[1] When the Radio Plasma Imager (RPI) on the IMAGE satellite operates in the inner plasmasphere and at moderate to low altitudes over the polar regions, pulses emitted at the low end of its 3-kHz to 3-MHz sounding frequency range can propagate in the whistler mode and/or in the Z mode. During soundings with both 25.6-ms pulses and 3.2-ms pulses, whistler mode echoes have been observed in (1) ''discrete,'' lightning whistlerlike forms and (2) diffuse, widely time spread forms suggestive of mode coupling at the boundaries of density irregularities. Discrete echoes have been observed at altitudes less than %5000 km both inside the plasmasphere and over the auroral and polar regions, being most common inside the plasmasphere. Diffuse echoes have also been observed at altitudes less than 5000 km, being most common poleward of the plasmasphere. Either discrete or diffuse echoes or both have been detected during one or more soundings on at least half of all IMAGE orbits. In regions poleward of the plasmasphere, diffuse Z mode echoes of a kind reported by Carpenter et al. (2003) were found to accompany both discrete and diffuse whistler mode echoes 90% of the time and were also present during 90% of the soundings when no whistler mode echoes were detected. It is proposed that the observed discrete whistler mode echoes are a consequence of RPI signal reflections at the bottom side of the ionosphere and that diffuse whistler mode echoes are a result of scattering of RPI signals by geomagnetic field-aligned electron density irregularities located within 2000 km earthward of the satellite and in directions close to that of the field line passing through IMAGE. Diffuse Z mode echoes are believed to be due to scattering of RPI signals from electron density irregularities within 3000 km of the satellite, particularly those in the generally cross-B direction. Consistent with previous works, our results indicate that the magnetosphere at high latitudes is highly structured, with electron density irregularities that exist over cross-B scales ranging from 10 m to 100 km and that profoundly affect whistler mode propagation. It is demonstrated that both kinds of whistler mode echoes as well as diffuse Z mode echoes have potential for local and remote diagnostics of electron density distributions and structures. , et al. (2004), Diagnostics of magnetospheric electron density and irregularities at altitudes <5000 km using whistler and Z mode echoes from radio sounding on the IMAGE satellite,

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“…[5] Irregular structure of VLF field and increase of its intensity in inhomogeneous ionosphere was observed in numerous DEMETER satellite measurements in the auroral region [Titova et al, 1984a;Titova et al, 1984b;Trakhtengerts and Titova, 1985;Basu, 1978;Reid, 1968;Sudan et al, 1973;Villain et al, 1985, Sonwalkar et al, 2001Baker et al, 2000;Groves et al, 1988;Seyler, 1990]. The increase of VLF field intensity was accompanied by a spectral broadening while the satellite crosses the area with inhomogeneous medium.…”

Section: Introductionmentioning

confidence: 99%

VLF electromagnetic field structures in ionosphere disturbed by Sura RF heating facility

et al. 2010

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[1] Observation of spatial VLF field structures in an artificially disturbed ionosphere is reported. The disturbed area with horizontal sizes ∼50 km in a quiet middle-latitude ionosphere was produced by the powerful RF Sura heating facility (56°1′N, 46°1′E). Measurements were carried out onboard the DEMETER satellite while passing the disturbed area at height ∼700 km. Spectra broadening (Df < ±1 kHz) and considerable (up to 30 dB) increase of signal intensity of VLF transmitters' signals were observed. The VLF field and electron density irregularities have similar spatial structure. The characteristics of the VLF field in disturbed by RF heating area are analyzed.Citation: Rapoport, V. O., V. L. Frolov, S.

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Whistler-mode wave-injection experiments in the plasmasphere with a radio sounder

Cited by 13 publications

References 57 publications

Magnetospherically reflected, specularly reflected, and backscattered whistler mode radio-sounder echoes observed on the IMAGE satellite: 1. Observations and interpretation

Magnetospherically reflected, specularly reflected, and backscattered whistler mode radio-sounder echoes observed on the IMAGE satellite: 1. Observations and interpretation

Diagnostics of magnetospheric electron density and irregularities at altitudes <5000 km using whistler and Z mode echoes from radio sounding on the IMAGE satellite

VLF electromagnetic field structures in ionosphere disturbed by Sura RF heating facility

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