The Radar Aurora

Hysell, D. L.

doi:10.1002/9781118978719.ch14

Cited by 18 publications

(27 citation statements)

References 99 publications

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“…The notion that the dominant structures have a mean Doppler shift given by

C_{s} \cos θ

in ordinary situations is backed up by the numerical simulations of Oppenheim et al [] and Oppenheim and Dimant [] and by observations going back to Bahcivan et al []. It has been used to analyze Type I and Type II waves [e.g., Hysell , , and references therein].…”

Section: Nonlinear Constructmentioning

confidence: 99%

A theoretical framework for the changing spectral properties of meter‐scale Farley‐Buneman waves between 90 and 125 km altitudes

St.-Maurice

Chau

2016

JGR Space Physics

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Stimulated by recent observations described in a companion paper, we have revisited existing theories of the Farley‐Buneman instability throughout the altitude range 90 to 125 km. We have assumed that the irregularities detected by radars at a given altitude are dominated by structures moving at the threshold speed in a direction associated with maximum linear growth rate conditions. We included recent nonisothermal electron and ion theories, which can modify threshold speeds by considerable amounts. We included altitude‐dependent models of ion and electron temperature and of the ion motion in the phase velocity calculations. Our treatment of the instability explains why some spectra are slow (Doppler shifts typically 200 m/s) and narrow, while others are fast (1500 m/s or close to the E × B) and narrow. These narrow spectra have all the characteristics of what has been labeled as “Type III” and “Type IV” in the past. Our calculations also offer an explanation for the observation of a strong asymmetry in the number of events with positive Doppler shifts near the nominal ion‐acoustic speed and those with negative Doppler shifts of the same magnitude.

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“…The notion that the dominant structures have a mean Doppler shift given by

C_{s} \cos θ

Section: Nonlinear Constructmentioning

confidence: 99%

A theoretical framework for the changing spectral properties of meter‐scale Farley‐Buneman waves between 90 and 125 km altitudes

St.-Maurice

Chau

2016

JGR Space Physics

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“…Oppenheim et al [2008] and Oppenheim and Dimant [2013b] have gone further, to suggest that the Doppler shifts and spectral widths of the backscatter should vary approximately as the cosine and sine of the flow angle, which would satisfy equation (1) as long as the threshold speed should be somewhat less than the ion acoustic speed, given that the spectral width of Type I waves is not negligible. With this caveat in mind Hysell [2015] has proposed that a pragmatic way to obtain information about the plasma drift from m-scale E region irregularities is to use the equation…”

Section: A13 the Connection Between Spectral Width And Mean Dopplermentioning

confidence: 99%

“…The recent advent of radar imaging has allowed for the resolution of time-space-frequency ambiguities and has offered an ability to discern more clearly the location of various spectral signatures and their evolution in a broader context. This has made it possible to resolve some of the previous ambiguities Journal of Geophysical Research: Space Physics 10.1002/2016JA023104 [e.g., Bahcivan et al, 2005] to the point that the expressions presented by Hysell [2015] above could be put to the test and were found to produce reasonable results. As we show in the present paper, our data set is offering further tests and insights into this approach based on a characterization of the different spectral peaks.…”

Section: Numerical Simulations Bymentioning

confidence: 99%

Unusual 5 m E region field‐aligned irregularities observed from Northern Germany during the magnetic storm of 17 March 2015

Chau

St.-Maurice

2016

JGR Space Physics

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Coherent E region echoes were observed during the 17 March 2015 storm at midlatitudes by multistatic wide field of view radars operating in northern Germany. Two of the stations operated in a monostatic configuration, while one link was set in bistatic mode. Interferometry made it feasible to locate the targets. While the radars were built to measure mesospheric winds from specular meteor echoes, the storm was so intense that it allowed them to observe auroral E region echoes for more than 4 h. All stations detected numerous examples of narrow spectra with slow (≈180 m/s) and fast (up to 1600 m/s) Doppler velocities. The target speeds were much faster than the Doppler velocities for the slow narrow echoes (more than 800 m/s versus 180 m/s) but comparable to the observed Doppler shift for the 1500 m/s narrow fast types. The narrow types came from localized horizontal structures 50 to 80 km wide in range. The fast narrow types came from the upper part of the altitudes associated with Farley‐Buneman waves. The slow narrow structures were typically from altitudes lower than 100 km. Unexpectedly, the great majority of the echoes associated with more ordinary ion acoustic turbulence had a positive Doppler shift and came from the east. A companion paper uses these new observations to reevaluate the origin of the narrow echoes and of the asymmetry in the counts. Irrespective of the generation mechanisms, our observations indicate that a combination of unusually large electric field and strong precipitation is needed to produce the unusual echoes.

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“…Since then, the aeronomy community has produced a substantial amount of observational and theoretical work on the subject of E-region coherent echoes. See the excellent reviews of the radar aurora by Makarevich (2009) and Hysell (2015) and of E-region instabilities in general by Fejer and Kelley (1980), Sahr and Fejer (1996), and Farley (2009) for more information. Bowles (1954) used a 25.4 MHz radar to study auroral echoes and determine that the radar aurora is highly aligned with the background magnetic field.…”

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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The Radar Aurora

Cited by 18 publications

References 99 publications

A theoretical framework for the changing spectral properties of meter‐scale Farley‐Buneman waves between 90 and 125 km altitudes

A theoretical framework for the changing spectral properties of meter‐scale Farley‐Buneman waves between 90 and 125 km altitudes

Unusual 5 m E region field‐aligned irregularities observed from Northern Germany during the magnetic storm of 17 March 2015

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

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