Photoelectron‐induced waves: A likely source of 150 km radar echoes and enhanced electron modes

Oppenheim, M. M.; Dimant, Y. S.

doi:10.1002/2016gl068179

Cited by 23 publications

(70 citation statements)

References 32 publications

(46 reference statements)

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“…We instead find that spectral width tends to increase with height, a feature that has been observed in incoherent scattered signals with increasing height (Chau & Kudeki, 2006). While the role of photoelectron-induced plasma waves resulting in NEIS in the 150-km region (Oppenheim & Dimant, 2016) can be understood, it was not clear as to how the plasma instability, generating FAI, sets in at the 150-km region, where neither background electric field nor plasma density gradient is significant.. Chau et al (2009) were the first to invoke the role of both NEIS and FAI in the echoing phenomenon.…”

Section: Discussionmentioning

confidence: 51%

“…The ubiquitous quasiperiodicity of the echoes (e.g., Kudeki & Fawcett, 1993) and inverse relationship between echo occurrence/intensity and solar EUV flux (Patra et al, 2017) provoke us to think about the roles of atmospheric gravity waves (AGW) and low background plasma density. Patra et al (2017) have outlined a hypothesis as to how AGW in the background of low neutral and plasma density could enhance the plasma wave processes through a photoelectron pathway proposed recently by Oppenheim and Dimant (2016). Patra et al (2017) have outlined a hypothesis as to how AGW in the background of low neutral and plasma density could enhance the plasma wave processes through a photoelectron pathway proposed recently by Oppenheim and Dimant (2016).…”

Section: Discussionmentioning

confidence: 99%

“…Scientists are pondering on two potential candidates involved in the echoing process: (1) field-aligned irregularities (FAI) generated by some kind of interchange instability (Kudeki & Fawcett, 1993;Patra & Rao, 2006;Tsunoda & Ecklund, 2004) and (2) naturally enhanced plasma waves (Chau et al, 2009;Oppenheim & Dimant, 2016). Scientists are pondering on two potential candidates involved in the echoing process: (1) field-aligned irregularities (FAI) generated by some kind of interchange instability (Kudeki & Fawcett, 1993;Patra & Rao, 2006;Tsunoda & Ecklund, 2004) and (2) naturally enhanced plasma waves (Chau et al, 2009;Oppenheim & Dimant, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications

et al. 2020

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We present and discuss common-volume dual-frequency radar observations of 150-km echoes made at 30 and 53 MHz from Gadanki by employing identical transmitter power and antenna beam width. These controlled experiments reveal that 150-km echoes are stronger, broader in spectral width, and more frequent in their occurrence at 30 MHz than at 53 MHz. Echo intensities at 30 and 53 MHz are found to be consistent with the rocket-borne observations of wave number spectrum of meter-scale irregularities in the 150-km region. The frequency dependence of spectral widths of the echoes while is found to be somewhat similar to that of electrojet type-1 echoes it is opposite to that of electrojet type-2 echoes and also to that of incoherent scattering in direction perpendicular to magnetic field. Spectral widths of the echoes observed by both radars are found to be independent of SNR. A detailed comparison of these observations with those made earlier suggests that instrument functions play an important role in manifesting SNR-dependent/independent spectral width property of the 150-km echoes. The narrow spectral properties and frequency dependence of echo intensity and spectral width clearly suggest that the irregularities responsible for the radar backscatter are linked with weak plasma turbulence and the meter-scale irregularities responsible for radar echoes ought to be growing with direct injection of energy at the meter scale itself to overcome damping. We surmise the potential role of photoelectrons and atmospheric gravity waves in the underline plasma instability process.

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Section: Discussionmentioning

confidence: 51%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications

et al. 2020

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“…Chau and Kudeki (2013), however, found that for perpendicular echoes, when spectral width is plotted as a function of SNR, majority of the echoes show SNR-dependent spectral width, that is, spectral width increases with SNR. This, however, by no means rule out the NEIS (Chau & Kudeki, 2013) or the recently proposed photo-electron induced plasma wave mechanism (Oppenheim & Dimant, 2016) responsible for radar echoes from the 150-km region. We find that echoes in the lower layer observed at 53 MHz clearly show spectral width linearly scaling with SNR.…”

Section: Discussionmentioning

confidence: 75%

First Dual‐Frequency Radar Observations of 150‐km Echoes From Gadanki and Implications

Patra

Chaitanya

Rao

et al. 2018

Geophysical Research Letters

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We present the first dual‐frequency overlapping volume radar observations of daytime 150‐km echoes made at 30 and 53 MHz from Gadanki, India. We show remarkably different responses of the 150‐km echoing layers including the spectral characteristics of the echoes at 30 and 53 MHz. Results show that while the echoes in general are remarkably stronger with narrower spectral width at 30 MHz than that of 53 MHz the relationship between radar cross sections at the two frequencies varies depending on the echoing layer. We also show distinctly different spectral broadening in different echoing regions observed by the 53‐MHz radar, which is missing in the 30‐MHz radar observations. These new observations indicate involvement of naturally enhanced incoherent scattering as well as scattering from enhanced electron density fluctuations of plasma instability origin and hence are of utmost importance in understanding the origin of the puzzling 150‐km echoing phenomenon.

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“…These waves are predominantly generated around 150 km where most of the solar EUV flux is absorbed. Recently, Oppenheim and Dimant (2016) modeled the effect of photoelectrons on the lower F region plasma using a particle-in-cell model and suggested that photoelectrons can generate electron waves that ultimately are responsible for plasma irregularities causing the enhanced radar backscatter. This is a similar region where we observe 150-km echoes ( Figure 1).…”

Section: Journal Of Geophysical Research: Space Physicsmentioning

confidence: 99%

Height Variation of Gaps in 150‐km Echoes and Whole Atmosphere Community Climate Model Electron Densities Suggest Link to Upper Hybrid Resonance

Lehmacher

Kudeki

et al. 2020

JGR Space Physics

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Radar echoes from the daytime lower F region near the magnetic equator, so-called 150-km echoes, have been puzzling researchers for decades. Neither the mechanisms that generate the enhanced backscatter at very high frequencies (typically 30-50 MHz), the sharp lower cutoff height, the intricate layering with multiple echo layers separated by narrow gaps, nor the modulation of the echoes by short-period gravity waves is well understood. Here we focus on the diurnal variation of the echo layers-specifically, certain wide gaps in the vertical structure-which apparently descend in the morning, reach their lowest altitude near local noon, and ascend in the afternoon, sometimes described as necklace structure based on the appearance of the layers in range-time-intensity diagrams. Analyzing high-resolution data obtained with the Jicamarca radar between 2005 and 2017, spanning more than one solar cycle, we find that (a) wide gaps and narrow lines occur in vertically stacked, systematically repeating pattern; (b) the gap heights vary with season and solar cycle; and (c) the gap heights can be associated with specific contours of plasma frequencies or electron densities. The last two findings are supported by simultaneous observations of VIPIR ionosonde reflection heights and by comparison of gap heights with electron density contours obtained with the WACCM-X 2.0 global model. Finally, the wide gaps appear to coincide with the double resonance condition, where the upper hybrid frequency equals integer multiples of the electron gyrofrequency. This may explain why field-aligned plasma irregularities are suppressed and enhanced radar backscatter is not observed inside the gaps.

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Photoelectron‐induced waves: A likely source of 150 km radar echoes and enhanced electron modes

Cited by 23 publications

References 32 publications

Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications

Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications

First Dual‐Frequency Radar Observations of 150‐km Echoes From Gadanki and Implications

Height Variation of Gaps in 150‐km Echoes and Whole Atmosphere Community Climate Model Electron Densities Suggest Link to Upper Hybrid Resonance

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