Collisionless Effects on the Spectrum of Secondary Auroral Electrons at Low Altitudes.

Papadopoulos, K.; Rowland, H. L.

doi:10.21236/ada049115

Cited by 4 publications

(5 citation statements)

References 10 publications

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“…For example, the distributions of auroral electrons observed at rocket altitudes [Kaufman et al, 1978] cannot be accounted for simply on the basis of their being accelerated by a static, field-aligned, electric field, even though there may be good evidence that this is the primary acceleration mechanism. It is known that nearly monoenergetic, field-aligned electron beams that would be produced by a parallel electric field are highly unstable and the instabilities are likely to modify the electron distributions significantly [Matthews et al, 1976;Papadopoulos and Rowland, 1978]. Such effects involving wave-particle interactions between the electron beam and the ambient ionospheric plasma, generation of hiss and auroral kilometric radiation, and collisional interactions between precipitating particles and the neutral atmosphere are beyond the scope of this review.…”

Section: Graphs Shown Inmentioning

confidence: 95%

Mechanisms for auroral precipitation: A review

Swift¹

1981

Reviews of Geophysics

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Theories for and observations relating to auroral precipitation are reviewed for purposes of assessing our understanding of the aurora and of identifying those processes which play the most important role in auroral precipitation. For purposes of the review, four categories of auroral forms are defined: (1) the diffuse aurora, which usually forms the equatorward boundary of the auroral oval, (2) auroral patches and pulsations, which appear most commonly within the morning sector of the diffuse aurora, (3) the discrete aurora, most prominently observed in the evening and poleward sectors of the auroral oval, and (4) the 'inverted-V' aurora, which appears in the same regions as discrete aurora but with much larger size scales. One principal conclusion is that the diffuse aurora, likely caused by both proton and electron precipitation, is the result of pitch angle scattering by electrostatic cyclotron waves. Another is that the auroral pulsations and patches are the result of pitch angle scattering of more energetic electrons by electromagnetic whistler mode waves. The patches may represent flux tubes of enhanced ionization tied to the lower ionosphere. The discrete aurora is the result of electron acceleration parallel to the magnetic field by the quasi-static electric field of a current-driven laminar electrostatic V shock. The theory for inverted-V precipitation is not well developed, but observations strongly suggest that it is related to ion cyclotron anomalous resistivity. INTRODUCTIONEver since the first sounding rockets penetrated the upper atmosphere over 20 years ago it has been known that the visible aurora has been caused by electron and proton impact upon the upper atmosphere. It has only been within the past few years that any fundamental understanding of the processes responsible for the precipitation of charged particles has emerged. The purpose of this revi• is to assess the state of of plasma instabilities to auroral problems. Although this analysis quantitatively treats a well-defined plasma model, some of the assumptions required for the instability to develop and some of the consequences of the theory have not been borne out by observations. Rather than presenting an exhaustive analysis of all precipitation mechanisms proposed in the literature, this review presents a critical assessment of current ideas for which there exists compelling observational eviour understanding of auroral particle precipitation and to at-dence. These ideas and the theories formulated from them are tempt to identify those processes which are likely to pla• a sig-' described in some detail. nificant role in auroral precipitation. This will involve both aThe aurora has such a variety of temporal and spatial size critical examination of the predictions of the various theoretical mechanisms for auroral precipitation and a review of observations relevant to the precipitation process.There are two basic types of precipitation processes: (1) ac-•:eleration into the atmosphere by quasi-stationary electric fields with a compone...

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Section: Graphs Shown Inmentioning

confidence: 95%

Mechanisms for auroral precipitation: A review

Swift¹

1981

Reviews of Geophysics

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“…By fixing the ions one prevents any low-frequency response by the plasma and the appearance of strong turbulence [Rowland and Papadopoulos, 1977]. In our case we do not have a collection of these structures to provide randomness so we do not end up with a smooth superthermal tail such as seen in the periodic simulations •Papadopoulos and Rowland, 1978]. As the beam energy is increased so is that of the superthermal electrons.…”

Section: Simulation Modelmentioning

confidence: 94%

“…They then showed that if there were a collection of such structures one could then write a diffusion equation for the acceleration process that would lead to the formation of a superthermal tail. In our case we do not have a collection of these structures to provide randomness so we do not end up with a smooth superthermal tail such as seen in the periodic simulations •Papadopoulos and Rowland, 1978]. Figure 7 and 8 show the results from a series of simulations.…”

Section: Simulation Modelmentioning

confidence: 97%

Generation of superthermal electrons by electron beams

Rowland¹

1988

J. Geophys. Res.

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A series of computer simulations is reported studying the coupling of a continuously injected cold electron beam into a warm background plasma. The simulations are performed in a finite length nonperiodic system. It is shown that strong turbulence determines the coupling of the beam to the ambient plasma and leads to the formation of superthermal electrons with velocities comparable to that of the injected beam. These electrons are accelerated both in the direction of the beam and back toward the gun. The superthermal electrons can carry return currents greater than the beam current. For active beam injection experiments in space, these particles provide a direct indication of the presence of the beam plasma interaction.

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“…This diffusion is too weak, however, to produce the apparent anisotropy in upgoing energy fluxes below the spectral peak [Reasoner and Chappell, 1973]. This effect is presumably associated with high-frequency turbulence and the accompanying velocity diffusion [Papadopoulos and Rowland, 1978;Maggs, 1982]. The diffusive acceleration model also does not yield a relation between the peak energy and the slope of the spectral tail as discussed by Lin and Hoffman [1979a].…”

Section: Plasma Sheet Precipitationmentioning

confidence: 99%

Diffusive acceleration of auroral primaries

Lotko¹

1986

J. Geophys. Res.

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The acceleration of electrons in a parallel electric field containing randomly distributed, micro double layers is investigated. The study is motivated by recent electric field observations in the auroral acceleration region. Its objective is to determine what effects stochastic versus static parallel electric fields may have on the spectral features of precipitating electrons. The average electron response as characterized by friction and diffusion coefficients is first analyzed. These coefficients are then used in a Fokker‐Planck equation for the altitudinal variation in the electron energy distribution. Electron sources at the top of the acceleration region (plasma sheet electrons) and at its latitudinal edges (ionospheric electrons) are included. It is shown that (1) the plasma sheet source gives rise to “inverted V” precipitation, as in quasi‐static models, and (2) the edge source is responsible for highly collimated, suprathermal precipitation. The spectral features of the former depend primarily on the average electric field and only weakly on its fluctuations. The properties of collimated precipitation are very sensitive to the microfield, however, owing to trapping phenomena. This analysis represents the first quantitative treatment of collimated electron precipitation; its predictions are in agreement with the observed intensity, pitch angle distribution, energy spectrum, and latitudinal width of edge region precipitation.

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Collisionless Effects on the Spectrum of Secondary Auroral Electrons at Low Altitudes.

Cited by 4 publications

References 10 publications

Mechanisms for auroral precipitation: A review

Mechanisms for auroral precipitation: A review

Generation of superthermal electrons by electron beams

Diffusive acceleration of auroral primaries

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