Comparing VHF coherent scatter from the radar aurora with incoherent scatter and all‐sky auroral imagery

Hysell, D. L.; Miceli, R. J.; Munk, J.; Hampton, D. L.; Heinselman, C. J.; Nicolls, M. J.; Powell, Steven P.; Lynch, K. A.; Lessard, M.

doi:10.1029/2012ja018010

Cited by 17 publications

(51 citation statements)

References 38 publications

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“…The two representations would be exactly analogous if all convection drift speeds were 350 m/s. Both are reminiscent of the results in the recent study by Hysell et al [] in which a reasonable agreement was obtained between the convection component measured by the Poker Flat incoherent scatter radar (PFISR) and the convection component implied by their coherent velocity measurements at 30 MHz and their assumed relationship

V_{ph} = V_{\circ} \cos ((), θ - θ_{\circ}),

where V ∘ =350 + ( V E /100) 2 in meters per second and θ ∘ is a small offset due to thermal effects. The above expression for the phase velocity has been suggested by experimental results of Bahcivan et al [] in the form with C s = V ∘ , which was further supported by simulations [ Oppenheim et al , ; Oppenheim and Dimant , ].…”

Section: Discussionsupporting

confidence: 84%

Electric field control of E region coherent echoes: Evidence from radar observations at the South Pole

2015

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Characteristics and formation mechanisms of E region plasma irregularities at high latitudes are investigated using observations with the newly deployed Super Dual Auroral Radar Network (SuperDARN) radar at the South Pole Antarctic station (SPS) near a magnetic latitude (MLAT) of 75°S. It is shown that E region echo occurrence at SPS exhibits a diurnal variation that is significantly different from those at auroral and polar cap latitudes. Moreover, analysis of major spectral populations also showed a distinct and previously unreported diurnal pattern. The plasma drift velocity estimates are derived at E region ranges of SPS, leveraging the SPS radar's position well within the MLAT region where SuperDARN convection estimates are well constrained by the data. It is shown that E region irregularity occurrence increases when the convection direction is within the SPS field of view and/or when the plasma drift component is comparable with the nominal ion‐acoustic speed Cs of 350 m/s. This is the expected behavior for irregularities generated directly by the modified two‐stream plasma instability (MTSI). On the other hand, irregularity velocity dependence on convection velocity showed an unexpected saturation at velocity values smaller than nominal Cs. It is demonstrated that the convection velocity at which irregularity velocity starts to differ from the convection component and to approach a maximum value is dependent on the magnetic aspect angle. Moreover, the maximum velocity value itself also depends on the aspect angle. The observed behavior is discussed in context of recent models that involve evolving aspect angles as a key characteristic of MTSI saturation.

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V_{ph} = V_{\circ} \cos ((), θ - θ_{\circ}),

Section: Discussionsupporting

confidence: 84%

Electric field control of E region coherent echoes: Evidence from radar observations at the South Pole

2015

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“…These spectral images predict that the flow angle of density irregularities driven by the pure FBI should increase with altitude. Quantitatively, the calculated centroid angles in all six panels of Figure 5 are larger than the value of −10 • that Uspensky et al (2003) and Hysell et al (2012) assume. This result is qualitatively consistent with the conclusion of Uspensky et al (2003) that the ion drift contribution to the relative drift velocity is important.…”

Section: 1029/2019ja027326mentioning

confidence: 63%

“…The angle between Journal of Geophysical Research: Space Physics 10.1029/2019JA027326 these two drifts is the flow angle. Hysell et al (2012) reported results from VHF coherent-scatter radar observations during a geomagnetic substorm over Alaska, with an emphasis on aspects of the radar aurora revealed through VHF radar imaging. Haldoupis et al (1984) also used STARE to make observations of a common volume in the high-latitude E-region.…”

Section: Introductionmentioning

confidence: 99%

The Farley‐Buneman Spectrum in 2‐D and 3‐D Particle‐in‐Cell Simulations

2020

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Since the 1960s, the Farley-Buneman instability has played an important role in probing the E-region ionosphere. The intervening years have seen significant progress in the linear theory of this instability, its relation to other instabilities, and some of its observational signatures. However, the saturation mechanism and nonlinear behavior remain open topics because of their role in controlling energy flow in the E-region plasma. This paper explores the saturated state of the Farley-Buneman instability in 2-D and 3-D kinetic simulations of the high-latitude ionosphere, at three different simulated altitudes: 107, 110, and 113 km. These simulations show irregularity amplitude growth and saturation in all runs, but irregularity growth takes much longer in 2-D than in 3-D. Once the simulations reach saturation, wave power in the meter-scale regime falls off as a power law below the wavelength of peak growth, but the power law index is larger in 3-D than in 2-D. At longer wavelengths, the 3-D spectrum is much flatter than the 2-D spectrum. This implies that purely 2-D simulations of the Farley-Buneman instability may overestimate irregularity amplitudes at decameter scales and may also underestimate the efficiency of ion Landau damping at the ion mean-free-path scale. From a physical perspective, the relatively flat spectra above the wavelength of peak growth in 3-D simulations imply a wavelength-independent saturation mechanism across a range of altitudes. Finally, both 2-D and 3-D simulations demonstrate the importance of accounting for zeroth-order ion drift when estimating the flow angle of density irregularities. Plain Language SummaryAt approximately 90-120 km in altitude, the Earth's atmosphere comprises a gas containing mostly neutral molecules, and a small number of positively charged ions and electrons. This sort of gas is called a weakly ionized plasma. Aeronomy researchers have known for decades that the weakly ionized plasma around 90-120 km in Earth's atmosphere can grow unstable and reflect radio waves, and they have used radio-wave reflection as one technique to probe this region of geospace. However, the aeronomy community still does not understand the nature of the fully developed plasma instabilities in this region. This work addresses that problem with computer simulations. It finds that 2-D simulations do not capture all the characteristics of 3-D simulations, which should mimic reality more closely. It also finds that whatever mechanism creates the fully developed 3-D instability should apply to wavelengths from a few meters to tens of meters. Finally, this work suggests that the direction along which the unstable waves travel should change in a predictable way as altitude increases. These conclusions will help future researchers estimate atmospheric parameters based on radar and rocket measurements.

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“…To incorporate flow angle effects into the heuristic model, we model the phase velocities and flow angles in terms of the Doppler spectral moments (Hysell et al, ):

d_{s} = v_{ph} \cos false(θ - θ_{0} false) + v_{n},

d_{ω} = α v_{ph} false| \sin false(θ - θ_{0} false) false| .

…”

Section: Estimation Of Flows From Spectral Datamentioning

confidence: 99%

Assessing Ionospheric Convection Estimates From Coherent Scatter From the Radio Aurora

2018

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Coherent radar backscatter spectra from auroral E region plasma irregularities can be measured with great precision and accuracy. The Doppler spectra obtained from those measurements can be used to estimate auroral convection patterns using an empirical model. These estimates are consistent with rocket, optical, and incoherent scatter radar data, but direct comparison between the different data sets is not straightforward. In order to establish the quality of the empirical model, alternative approaches are then needed. In this work, we use the electrostatic nature of the convection electric field to assess the physical consistency of the empirical model: The model will be satisfactory to the extent that the convection patterns derived from them are incompressible. The incompressibility criteria were assessed for the estimated convection patterns obtained from the substorm of 20 December 2015. Two different approaches were used for this assessment. First, an electrostatic potential was fitted to the convection pattern produced by the empirical model. A good fit implies that there exists an incompressible convection pattern consistent with the Doppler spectra measurements. Second, the uncertainties on the Doppler spectral estimates where propagated through the empirical model to calculate the expected uncertainties on the divergence of the convection field obtained directly from the empirical model. The convection field will be incompressible if its divergence lies within the uncertainty estimates. Both approaches indicate that the evaluated convection patterns are consistently incompressible.

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Comparing VHF coherent scatter from the radar aurora with incoherent scatter and all‐sky auroral imagery

Cited by 17 publications

References 38 publications

Electric field control of E region coherent echoes: Evidence from radar observations at the South Pole

Electric field control of E region coherent echoes: Evidence from radar observations at the South Pole

The Farley‐Buneman Spectrum in 2‐D and 3‐D Particle‐in‐Cell Simulations

Assessing Ionospheric Convection Estimates From Coherent Scatter From the Radio Aurora

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