Generation of small-scale irregularities in the equatorial electrojet

Sudan, R. N.; Akinrimisi, Jibayo; Farley, D. T.

doi:10.1029/ja078i001p00240

Cited by 349 publications

(282 citation statements)

References 26 publications

(8 reference statements)

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“…Both E-region instabilities create propagating compressional plasma density waves which drive nonlinear currents as illustrated by Fig. 1 (Sudan et al, 1973). The two-stream growth-rate equation (2) predicts that the electron flow becomes linearly unstable and will experience wave growth when…”

Section: Theory Of Wave-driven Currentsmentioning

confidence: 99%

“…We show that wave-driven electron currents can cause these squared-off electric fields through a two-step process. First, the perturbed electric field of a gradient-drift wave must exceed the threshold necessary to initiate two-stream waves (Sudan et al, 1973). Second, these secondary two-stream waves generate wave-driven electron currents which modify the original gradient-drift waves.…”

Section: Gradient-drift Wave Simulationmentioning

confidence: 99%

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Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet

Oppenheim

1997

Ann. Geophys.

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Abstract. Ionospheric two-stream waves and gradientdrift waves nonlinearly drive a large-scale (D.C.) current in the E-region ionosphere. This current flows parallel to, and with a comparable magnitude to, the fundamental Pedersen current. Evidence for the existence and magnitude of wave-driven currents derives from a theoretical understanding of E-region waves, supported by a series of nonlinear 2D simulations of two-stream waves and by data collected by rocket instruments in the equatorial electrojet. Wave-driven currents will modify the large-scale dynamics of the equatorial electrojet during highly active periods. A simple model shows how a wave-driven current appreciably reduces the horizontally flowing electron current of the electrojet. This reduction may account for the observation that type-I radar echoes almost always have a Doppler velocity close to the acoustic speed, and also for the rocket observation that electrojet regions containing gradientdrift waves do not appear also to contain horizontally propagating two-stream waves. Additionally, a simple model of a gradient-drift instability shows that wavedriven currents can cause nonsinusoidal electric fields similar to those measured in situ.

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Section: Theory Of Wave-driven Currentsmentioning

confidence: 99%

Section: Gradient-drift Wave Simulationmentioning

confidence: 99%

Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet

Oppenheim

1997

Ann. Geophys.

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“…In a simple model, with a horizontally strati®ed sporadic-E layer, the gradient drift mode can produce waves with k vector lying mainly in the E-W direction (primary waves) so that a northwards-looking radar might only observe secondary waves generated by the gradient resulting from the primary waves, as explained by Sudan et al (1973). The real situation can be more complicated in irregular layers, for instance in partially re¯ecting layers and in spread Es (From and Whitehead, 1986) inside which one can expect that non-vertical density gradients also exist.…”

Section: Introductionmentioning

confidence: 99%

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

Bourdillon¹,

Lefur²,

Haldoupis

et al. 1997

Ann Geophysicae

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Abstract. HF radar observations of mid-latitude sporadic-E irregularities carried out with the Valensole radar in South France are compared with simultaneous ionosonde measurements underneath the irregularity zones. In a previous study of Valensole radar data, it has been shown that HF backscatter from the night-time mid-latitude E region is usually associated with largescale wave-like modulations. To obtain more information on the geophysical conditions prevailing during backscatter events, a new experiment was performed which also included a vertical ionosonde beneath the scattering region. The data to be presented here are from two periods when radar scattering appeared simultaneously with large variations in the virtual height and the Doppler velocity of F-layer re¯ected echoes measured with the vertical ionosonde, indicating very clearly the passage of atmospheric gravity waves (AGWs). The e ect of the atmospheric waves on the sporadic-E layer is not always as marked as it is in the F region. In the ®rst event, the passage of the AGWs is accompanied by an upward followed by a downward movement of the Es-layer. The apparent descending movement of the Es-layer from 135 to 110 km in less than 10 min corresponded to a positive (downward) Doppler velocity of 35 m/s measured by the vertical ionosonde, and was accompanied by a range variation in the radar scattering region with a negative rate of about 90±110 m/s. In the second event, the Es-layer is not as strongly disturbed as in the previous one, but, nevertheless, the range variations of the scattering region can still be associated with height¯uctuations of the Es-layer.

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“…The mechanism behind the production of these "two-step" Type I waves was uncovered by Sudan et al (1973). Basically, the electrojet first excites primary waves in the east-west direction on a scale of a few km.…”

Section: Vertical Type I Echoes At Low Latitudesmentioning

confidence: 99%

The influence of non-isothermal electrons and neutral wind structures on the doppler properties of vertical m-size field-aligned irregularities in the low latitude E-region

St.-Maurice¹,

Choudhary²

2007

Rev. Bras. Geof.

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ABSTRACT.Meter size irregularities are routinely studied with radars in the equatorial and low latitude regions. In both instances echoes from the E-region (90 to 120 km altitude) are a common occurrence. The resulting echoes are labeled as so-called Type I or Type II according to their spectral signature. In this paper we show that the phase velocity of Type I echoes increases with decreasing altitude owing to thermal feedback effects taking place in the growth process. We also show that Type II echoes can be influenced by atmospheric neutral winds to the point of revealing the presence of Kelvin-Helmholtz billows, as shown by a recently studied example taken from the Gadanki radar in India.Keywords: equatorial electrojet, plasma waves and instabilities, ionospheric irregularities, low latitude E-region, VHF radar spectra, quasi-periodic echoes, KelvinHelmholtz billows, turbulence.RESUMO. Irregularidades com escala de metros são estudadas rotineiramente com radares nas regiões de baixas latitudes e equatoriais. Em ambos os estudosé comum a ocorrência de ecos da região E (90 a 120 km de altitude). Os ecos resultantes são denominados de Tipo I e Tipo II de acordo com sua assinatura espectral. Neste trabalho nós mostramos que a velocidade de fase dos ecos tipo I aumentaà medida que diminui a altitude devido a efeitos térmicos causados pela própria irregularidade durante seu processo de desenvolvimento. Nós também mostramos que os ecos do Tipo II podem ser influenciados pelos ventos neutros atmosféricos ao ponto de revelar a presença de ondas do tipo Kelvin-Helmholtz, conforme demonstrado em alguns exemplos de estudos recentes realizados com o radar Gadanki naÍndia.Palavras-chave: eletrojato equatorial, ondas de plasma e instabilidades, irregularidades ionosféricas, região E em baixas latitudes, espectros obtidos com radares em VHF, ecos quase-periódicos, ondas do tipo Kelvin-Helmholtz, turbulência.

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Generation of small-scale irregularities in the equatorial electrojet

Cited by 349 publications

References 26 publications

Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet

Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

The influence of non-isothermal electrons and neutral wind structures on the doppler properties of vertical m-size field-aligned irregularities in the low latitude E-region

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