Large aspect angles in auroral <i>E</i> region echoes: A self‐consistent turbulent fluid theory

Hamza, A. M.; Maurice, Jean

doi:10.1029/94ja03026

Cited by 15 publications

(13 citation statements)

References 35 publications

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“…Nonlinear theories have been invoked in the past in order to explain plasma wave generation at large flow (Sudan et al, 1973) and aspect angles (e.g. Hamza and St-Maurice, 1995). Of special interest for this study is the recent work by Drexler and St.-Maurice (2005) who proposed that what appears as large aspect angle echoes in the HF radar data can in fact be successfully interpreted using the nonlocal formulation of Drexler et al (2002).…”

Section: E-region Irregularity Generation At Large Flow and Aspect Anmentioning

confidence: 99%

A first comparison of irregularity and ion drift velocity measurements in the E-region

et al. 2006

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Abstract. E-region irregularity velocity measurements at large flow angles with the STARE Finland coherent VHF radar are considered in context of the ion and electron velocity data provided by the EISCAT tristatic radar system, CUTLASS Finland coherent HF radar, and IMAGE fluxgate magnetometers. The data have been collected during a special experiment on 27 March 2004 during which EISCAT was scanning between several E-and one F-region altitudes along the magnetic field line. Within the E-region, the EISCAT measurements at two altitudes of 110 and 115 km are considered while the electron velocity is inferred from the EISCAT ion velocity measurements at 278 km. The lineof-sight (l-o-s) VHF velocity measured by STARE V VHF los is compared to the ion and electron velocity components (V i0 comp and V e0 comp ) along the STARE l-o-s direction. The comparison with V e0 comp for the entire event shows that the measurements exhibit large scatter and small positive correlation. The correlation with V e0 comp was substantial in the first half of the interval under study when V e0 comp was larger in magnitude. The comparison with V i0 comp at 110 and 115 km shows a considerable positive correlation, with VHF velocity being typically larger (smaller) in magnitude than V i0 comp at 110 km (115 km) so that V VHF los appears to be bounded by the ion velocity components at two altitudes. It is also demonstrated that the difference between V VHF los and V i0 comp at 110 km can be treated, in the first approximation, as a linear function of the effective backscatter height h eff also counted from 110 km; h eff varies in the range 108-114 km due to the altitude integration effects in the scattering cross-section. Our results are consistent with the notion that Correspondence to: R. A. Makarevich (r.makarevich@latrobe.edu.au) VHF velocity at large flow angles is directly related to the ion drift velocity component at an altitude h eff .

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Section: E-region Irregularity Generation At Large Flow and Aspect Anmentioning

confidence: 99%

A first comparison of irregularity and ion drift velocity measurements in the E-region

et al. 2006

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“…This raises an intriguing issue in view of the fact that observations indicate that waves often move at the threshold speed even when the electric field is strong enough to excite waves that could be moving much faster than that. Several nonlinear theories have proposed that the frequency could match the threshold speed by having the eigenfrequency changed nonlinearly through, for example, anomalous diffusion [ Robinson , 1986; St.‐Maurice , 1987] or mode‐coupling [ Hamza and St.‐Maurice , 1995a, 1995b]. The question that then arises, particularly at high latitudes, is this: if the electric field exceeds the threshold value, should we be using the results discussed in section 4.2 or should we find the solution to zero growth independently, given that has some explicit electron drift term into it, by contrast to the isothermal case?…”

Section: Threshold Conditions For the Farley‐buneman Instability In Tmentioning

confidence: 99%

Impact of electron thermal effects on Farley‐Buneman waves at arbitrary aspect angles

Kagan

St.-Maurice

2004

J. Geophys. Res.

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[1] Using a standard 8-moment expansion of the fluid equations, we have extended fluid calculations of the effect of electron temperature feedback on the linear Farley-Buneman instability theory to include the contribution of field-aligned heat flow and field-aligned wave electric fields through nonzero-aspect angles. Our treatment includes arbitrary ion magnetization and neutral winds but is limited, for simplicity, to zero flow angles. Our results indicate that, for 3-m waves, electron thermal corrections are significant (threshold phase velocities greater than predicted by isothermal theory by 20% or more) at aspect angles less than 0.35°for altitudes less than 103 km. Similar but smaller numbers are obtained for 10-m waves. The impact of the thermal corrections normally also decreases rapidly with increasing altitude. These results provide a straightforward explanation for equatorial observations of 3-m phase velocities that are at least 30% greater than the isothermal ion-acoustic speed below 105 km in the equatorial regions. The altitude dependence of the observed phase speeds also mimics very well the behavior seen in our calculations. The implication is that the aspect angles of the structures must be smaller than 0.3°. This is consistent with recent findings from radar interferometry.

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“…Farley, 2009). However, nonlinear and nonlocal processes may provide some support to the waves at large aspect angles through an increase in the scattering of electrons (Hamza and St-Maurice, 1995) and through a mode conversion at a spatial discontinuity in the aspect angle (Drexler and St.-Maurice, 2005), respectively, with the latter scenario being applicable mostly to decameter waves.…”

Section: Discussionmentioning

confidence: 99%

HF echo types revisited: aspect angle attenuation effects

Makarevich

Carter

2009

Ann. Geophys.

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Abstract. The high-spatial-resolution observations of the auroral E-region echoes by the Super Dual Auroral Radar Network (SuperDARN) HF radar at Pykkvibaer, Iceland considered in a previous study are re-examined. Both the spectral power and Doppler velocity of the E-region HF echoes exhibit strong dependence on the slant range and expected off-perpendicular magnetic aspect angle (aspect angle attenuation). We consider the aspect angle attenuation effects in identification of spectral HF echo types. It is argued that echoes with Doppler velocities close to the nominal value of the ion-acoustic speed C s (∼350 m/s) and echoes with velocities greatly exceeding the C s (up to 600 m/s) are more related in their generation mechanisms than previously thought. It is proposed to treat the echoes near the C s as aspect-angle-attenuated counterparts of the high-velocity echoes and that both types are generated directly by the modified two-stream instability with aspect angle attenuation resulting in the preferential phase velocity saturation at the C s .

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Large aspect angles in auroral E region echoes: A self‐consistent turbulent fluid theory

Cited by 15 publications

References 35 publications

A first comparison of irregularity and ion drift velocity measurements in the E-region

A first comparison of irregularity and ion drift velocity measurements in the E-region

Impact of electron thermal effects on Farley‐Buneman waves at arbitrary aspect angles

HF echo types revisited: aspect angle attenuation effects

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