Radar studies of long‐wavelength waves associated with mid‐latitude sporadic <i>E</i> layers

Riggin, D. M.; Swartz, Wesley E.; Providakes, J.; Farley, D. T.

doi:10.1029/ja091ia07p08011

Cited by 149 publications

(113 citation statements)

References 30 publications

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“…1, the echo intensity variations are followed rather closely, although not always in phase, by a wavelike variation in Doppler velocity. Actually, the velocity fluctuates mostly between ± 100 m/s, in good agreement with similar 50-MHz observations reported before by Ecklund et al (1981) and Riggin et al (1986). Figure 1 shows that the observed spectra are basically type 2, that is , rather broad with their mean (or peak) Doppler velocities near and around zero Doppler shift.…”

Section: The Experimentssupporting

confidence: 79%

Type-1 echoes from the mid-latitude E-Region ionosphere

Haldoupis¹,

Farley²,

Schlegel³

1997

Ann. Geophys.

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Abstract. This paper presents more data on the properties of type-1 irregularities in the nighttime midlatitude E-region ionosphere. The measurements were made with a 50-MHz Doppler radar system operating in Crete, Greece. The type-1 echoes last from several seconds to a few minutes and are characterized by narrow Doppler spectra with peaks corresponding to wave phase velocities of 250-350 m/s. The average velocity of 285 m/s is about 20% lower than nominal Eregion ion-acoustic speeds, probably because of the presence of heavy metallic ions in the sporadic-E-layers that appear to be associated with the mid-latitude plasma instabilities. Sometimes the type-1 echoes are combined with a broad spectrum of type-2 echoes; at other times they dominate the spectrum or may appear in the absence of any type-2 spectral component. We believe these echoes are due to the modified two-stream plasma instability driven by a polarization electric field that must be larger than 10 mV/m. This field is similar in nature to the equatorial electrojet polarization field and can arise when patchy nighttime sporadic-E-layers have the right geometry.

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Section: The Experimentssupporting

confidence: 79%

Type-1 echoes from the mid-latitude E-Region ionosphere

Haldoupis¹,

Farley²,

Schlegel³

1997

Ann. Geophys.

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“…Mid-latitude sporadic-E scattering is regularly observed by HF and VHF radars during summer at night (Goodwin, 1965;Ecklund et al, 1981;Tanaka and Venkateswaran, 1982a, b;Keys and Andrews, 1984;Riggin et al, 1986;Fukao et al, 1991;Yamamoto et al, 1991Yamamoto et al, , 1992Yamamoto et al, , 1994Haldoupis and Schlegel, 1993;Bourdillon et al, 1995); nevertheless, this phenomenon is not yet fully understood.…”

Section: Introductionmentioning

confidence: 99%

“…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. VHF and HF radar observations revealed that the scattering layer is very often a ected by spatial modulation of the backscattered power and also of the Doppler shift and width (Riggin et al, 1986;Fukao et al, 1991;Yamamoto et al, 1991Yamamoto et al, , 1992Yamamoto et al, , 1994Bourdillon et al, 1995). Riggin et al (1986) attributed their observed large-scale structures and the associated high velocities, sometimes exceeding 250 m/s, to kilometer-scale plasma waves generated by the gradient drift instability.…”

Section: Introductionmentioning

confidence: 99%

“…VHF and HF radar observations revealed that the scattering layer is very often a ected by spatial modulation of the backscattered power and also of the Doppler shift and width (Riggin et al, 1986;Fukao et al, 1991;Yamamoto et al, 1991Yamamoto et al, , 1992Yamamoto et al, , 1994Bourdillon et al, 1995). Riggin et al (1986) attributed their observed large-scale structures and the associated high velocities, sometimes exceeding 250 m/s, to kilometer-scale plasma waves generated by the gradient drift instability. This interpretation was disputed by Woodman et al (1991) because the width of an Es-layer is too small for the gradient drift mode to be operating at the kilometer scale.…”

Section: Introductionmentioning

confidence: 99%

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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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“…This has been a surprise at first because it had long been thought that the only places with the right combination of electric fields and density gradients were the equatorial electrojet region with its combination of strong currents and ambient density gradients and the auroral regions with their very strong ambient electric fields. However, following their initial discovery at mid latitudes, in association with sporadic E layers, (Tanaka & Venkateswaran, 1982;Ecklund et al, 1981;Riggin et al, 1986) it has become clear that E-region echoes have a rich morphology even at mid and low latitudes, as witnessed by so-called quasiperiodic (QP) echo patterns (Yamamoto et al, 1991;Choudhary & Mahajan, 1999;Chau & Woodman, 1999). In fact, while the association with sporadic E layers seems clear, it is interesting to note that some of the echoes at mid latitudes have Doppler shifts of the order of a few 100 m/s, which is clearly larger than any ambient electric field could provide (Haldoupis et al, 1997).…”

Section: Introductionmentioning

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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Radar studies of long‐wavelength waves associated with mid‐latitude sporadic E layers

Cited by 149 publications

References 30 publications

Type-1 echoes from the mid-latitude E-Region ionosphere

Type-1 echoes from the mid-latitude E-Region ionosphere

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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