Fast hisslers in substorms

Siren, J. C.

doi:10.1029/ja080i001p00093

Cited by 23 publications

(25 citation statements)

References 6 publications

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“…Ducts are field‐aligned enhanced or depressed columns of ionization, typically ≈0.1 L in width, that extend over long distances, often from one hemisphere to the other. It is generally accepted that ducts are responsible for the observation on the ground of lightning‐generated whistlers [ Helliwell , 1965] as well as impulsive auroral hiss [ Siren , 1975; Sonwalkar and Harikumar , 2000] These waves could not otherwise have reached the ground because of the total internal reflection within the ionosphere expected for nonducted whistler mode waves propagating (typically) at large wave normal angles.…”

Section: Discussionmentioning

confidence: 99%

“…Unlike ducts required for propagation of lightning whistlers, these ducts need not extend from hemisphere to hemisphere, and may have density enhancements of ∼50% or more. Such ducts are frequently present in the highly structured plasma at high latitude [ Persoon et al , 1983, 1988] and have been proposed to explain the propagation of impulsive auroral hiss to the ground [ Siren , 1975; Sonwalkar and Harikumar , 2000]. Because of the relatively short propagation distances involved, waves with wave normal angles other than those very close to B may remain within the duct both before and after reflection.…”

Section: Ray‐tracing Interpretation Of Observed Whistler and Accompanmentioning

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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Section: Discussionmentioning

confidence: 99%

Section: Ray‐tracing Interpretation Of Observed Whistler and Accompanmentioning

confidence: 99%

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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“…This range includes the source region altitudes suggested by both ground and satellite measurements [Siren 1972[Siren , 1975 Thus at a given altitude, for a given energy of electrons, cos0 is much smaller for lower frequencies and therefore the/• required to satisfy (1) is large, and this requires 0 to be much closer to 0/t compared to the 0 at higher frequencies. Later (section 2.2) we shall show that this requirement implies that IAH observed on the ground is generated at higher altitudes for lower frequencies, giving the observed frequency dispersion on the ground.…”

Section: The Source Region and The Generation Ofmentioning

confidence: 99%

“…There is also a discrepancy in the source altitude location of AH as determined from the spacecraft and ground observations. Ground observation estimates by Siren [1972Siren [ , 1975 and Makita [1979] place the AH source altitudes at values ~20,000 km for 10 kHz AH. Satellite observations and analysis of one case of AH data from the DE I satellite by Gumeft ½t al.…”

mentioning

confidence: 99%

“…Siren [!972, 1975] and Makita [1979] have tried to explain AH propagation to ground in terms of ducted propagation. Siren [1975] performed a dispersion analysis on impulsive hiss assuming that auroral hiss was propagating with its wave normal parallel to the geomagnetic field, an assumption that is not valid for auroral hiss which is generated at large wave-normal angles. Makita [1979] assumed that a magnetospheric duct terminates abruptly at 3000 km where hiss exits at all possible wave-normal angles.…”

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confidence: 99%

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An explanation of ground observations of auroral hiss: Role of density depletions and meter‐scale irregularities

Sonwalkar¹,

Harikumar²

2000

J. Geophys. Res.

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Abstract. Auroral hiss is one of the most intense whistler mode plasma wave phenomena observed both on the ground at high latitudes and on spacecraft in the auroral zone. Propagation of auroral hiss from its source region to the ground is poorly understood. The standard whistler mode propagation in a smooth magnetosphere predicts that auroral hiss generated at large wave-normal angles along the auroral field lines by Cerenkov resonance cannot penetrate to the ground. We show that the presence of density depletions along the field lines in the auroral zone and meter-scale density irregularities at altitudes < 5000 km at high latitude permits the auroral hiss propagation to the ground. In our mechanism the auroral hiss generated at high altitudes (> 5000-20,000 km) propagates to lower altitudes (< 3000-5000 km) in two modes: (1) a ducted mode guided by field-aligned density depletions and (2) a nonducted mode. The hiss with large wave-normal angle arriving at < 5000 km altitude is scattered by meter-scale irregularities, and about 0.1% to 10% of the scattered hiss has small wave-normal angles which can penetrate to the ground. Our mechanism explains the following features of auroral hiss observed on the ground: (1) the characteristic spectra of continuous and impulsive auroral hiss, (2) the upper and lower frequency cutoffs, (3) the dispersion of impulsive auroral hiss, (4) the location of ionospheric exit points of auroral hiss with respect to visible aurora, and (5) the 2-5 order of magnitude intensity decrease of auroral hiss observed on the ground relative to that observed on spacecraft. Based on the model presented here, we provide methods to infer parameters of density depletions and intensity of lower hybrid waves stimulated by auroral hiss from the ground measurements of auroral hiss together with optical and radar measurements.

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Further evidence for a connection between auroral kilometric radiation and ground‐level signals measured in Antarctica

et al. 2015

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(2015), Further evidence for a connection between auroral kilometric radiation and ground-level signals measured in Antarctica, J. Geophys. Res. Space Physics, 120, 2061-2075, doi:10.1002 Polarization measurements of one event show it to be right-hand polarized. Correlation analysis of ground-level and satellite data suggests an imperfect correlation with 2-3 sigma significance, although occasionally much better. (Perfect correlation is not expected, for at least two reasons: distant satellites detect AKR from many sources over a significant part of the oval, and many effects can hinder transmission of AKR from those sources to either distant satellites or ground stations.) Statistical analysis of the existing quantity of data is therefore suggestive but does not prove a connection between the ground-level AKR-like signals and outgoing AKR. However, two other methods provide evidence favoring such a connection. The first full-resolution measurements of ground-level AKR-like signals show that their fine structure strongly resembles that of AKR as known from high-resolution spacecraft receivers. Two case studies show that the location of active aurora, presumed connected with the AKR sources, controls whether or not the ground station detects the AKR, or which of several ground stations detects it most strongly. These investigations strengthen the hypothesis that through some mechanism, sources of outgoing AKR detected by distant satellites occasionally generate signals detectable as whistler mode waves at low altitude or right-hand polarized signals at ground level.

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Fast hisslers in substorms

Cited by 23 publications

References 6 publications

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

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

An explanation of ground observations of auroral hiss: Role of density depletions and meter‐scale irregularities

Further evidence for a connection between auroral kilometric radiation and ground‐level signals measured in Antarctica

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