A turbulent theoretical framework for the study of current‐driven E region irregularities at high latitudes: Basic derivation and application to gradient‐free situations

Hamza, A. M.; St.-Maurice, J.-P.

doi:10.1029/92ja02836

Cited by 73 publications

(80 citation statements)

References 32 publications

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“…According to this approach the microturbulence associated with the growth of a particular wave creates an increase in electron scattering that only stops when the scattering is intense enough to stop the growth of the unstable waves. Hamza and St.-Maurice (1993) proposed modecoupling as an alternative mechanism. According to that scheme, the energy of a mode is given o to other modes so that on average the growth rate ends up being zero while the spectrum broadens.…”

Section: Extrapolation To the Nonlinear Regimementioning

confidence: 99%

The role played by thermal feedback in heated Farley-Buneman waves at high latitudes

St.-Maurice

Kissack

2000

Ann. Geophys.

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Abstract. It is becoming increasingly clear that electron thermal e ects have to be taken into account when dealing with the theory of ionospheric instabilities in the high-latitude ionosphere. Unfortunately, the mathematical complexity often hides the physical processes at work. We follow the limiting cases of a complex but systematic generalized¯uid approach to get to the heart of the thermal processes that a ect the stability of E region waves during electron heating events. We try to show as simply as possible under what conditions thermal e ects contribute to the destabilization of strongly ®eld-aligned (zero aspect angle) Farley-Buneman modes. We show that destabilization can arise from a combination of (1) a reduction in pressure gradients associated with temperature¯uctuations that are out of phase with density¯uctuations, and (2) thermal di usion, which takes the electrons from regions of enhanced temperatures to regions of negative temperature¯uctu-ations, and therefore enhanced densities. However, we also show that, contrary to what has been suggested in the past, for modes excited along the E 0 Â B direction thermal feedback decreases the growth rate and raises the threshold speed of the Farley-Buneman instability. The increase in threshold speed appears to be important enough to explain the generation of`Type IV' waves in the high-latitude ionosphere.

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Section: Extrapolation To the Nonlinear Regimementioning

confidence: 99%

The role played by thermal feedback in heated Farley-Buneman waves at high latitudes

St.-Maurice

Kissack

2000

Ann. Geophys.

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“…Machida and Goertz (1988), as well as Thiemann and Schlegel (1994), used two-dimensional particle simulations in the plane made by the magnetic field and the E×B directions. This approach does not allow mode-coupling in the plane perpendicular to the magnetic field, which appears to be a substantial sink of energy for electric fields less than 50 mV/m (Hamza and St.-Maurice, 1993a). Nevertheless, Machida and Goertz (1988) focused on the electron heating question and concluded that the electrons were heated by perpendicular fluctuation fields through what they attributed to be anomalous collisions in spite of the geometrical problems associated with this mechanism.…”

Section: Introductionmentioning

confidence: 99%

“…The limited success of the anomalous diffusion concept led Hamza and St.-Maurice (1993a) to explore the consequences of mode-coupling under strongly growing FarleyBuneman conditions. They found that as long as the nonlinear evolution is dominated by coupling between modes that are perpendicular to B, the waves should indeed saturate at a phase velocity equal to the ion-acoustic speed, while the spectral width would increase to become, in velocity units, comparable to the ion-acoustic speed at right angles to the flow.…”

Section: Introductionmentioning

confidence: 99%

New insights from a nonlocal generalization of the Farley-Buneman instability problem at high latitudes

et al. 2002

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Abstract. When their growth rate becomes too small, the Eregion Farley-Buneman and gradient-drift instabilities switch from absolute to convective. The neutral density gradient is what gives the instabilities their convective character. At high latitudes, the orientation of the neutral density gradient is close to the geomagnetic field direction. We show that this causes the wave-vector component along the geomagnetic field to increase with time. This in turn leads to wave stabilization, since the increase goes hand-in-hand with an increase in parallel electric fields that ultimately short-circuits the irregularities. We show that from an equivalent point of view, the increase in the parallel wave vector is accompanied by a large upward group velocity that limits the time during which the perturbations are allowed to grow before escaping the unstable region. The goal of the present work is to develop a systematic formalism to account for the propagation and the growth/decay of high-latitude Farley-Buneman and gradient-drift waves through vertical convective effects. We note that our new formalism shies away from a plane wave decomposition along the magnetic field direction. A study of the solution to the resulting nonlinear aspect angle equation shows that, for a host of initial conditions, jump conditions are often triggered in the parallel wave-vector (defined here as the vertical derivative of the phase). When these jump conditions occur, the waves turn into strongly damped ionacoustic modes, and their evolution is quickly terminated. We have limited this first study to Farley-Buneman modes and to a flow direction parallel to the electron E × B drift. Our initial findings indicate that, irrespective of whether or not a jump in aspect angle is triggered by initial conditions, the largest amplitude modes are usually near the ion-acoustic speed of the medium (although Doppler shifted by the ion motion), unless the growth rates are small, in which case the waves tend to move at the same drift as the ambient electrons.

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“…The Doppler width can be linked either with larger-scale turbulence (i.e., variations in the free energy source in space and time) or with the lifetime of the irregularities. This means that all other things being equal, fast growth or decay rates should be associated with wider spectra and conversely for weakly growing or decaying modes [e.g., Hamza and St-Maurice, 1993a]. …”

mentioning

confidence: 99%

HF detection of slow long‐lived E region plasma structures

Jayachandran¹,

Maurice²,

MacDougall³

et al. 2000

J. Geophys. Res.

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A turbulent theoretical framework for the study of current‐driven E region irregularities at high latitudes: Basic derivation and application to gradient‐free situations

Cited by 73 publications

References 32 publications

The role played by thermal feedback in heated Farley-Buneman waves at high latitudes

The role played by thermal feedback in heated Farley-Buneman waves at high latitudes

New insights from a nonlocal generalization of the Farley-Buneman instability problem at high latitudes

HF detection of slow long‐lived E region plasma structures

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