Production of flickering aurora and field‐aligned electron flux by electromagnetic ion cyclotron waves

Abstract

Recent observations have suggested that flickering aurora is produced by a modulation of the field-aligned component of the electron flux within an auroral arc. It is proposed that a portion of the field-aligned electrons are of ionospheric origin and that these electrons are accelerated and their flux modulated by electromagnetic ion cyclotron waves that occur below the main acceleration region on auroral •rc field lines. A model of the electromagnetic ion cyclotron wave shows that the parallel phase velocity of the wave increases as the wave propagates toward the ionosphere. A test particle calculation shows that ionospheric electrons trapped or reflected by the wave are accelerated to energies of several keV and that their flux is modulated at the wave frequency. The relative amplitudes of the model wave electric fields are consistent with the observations of sm•llscale low-frequency ionospheric and magnetospheric electric fields near auroral •rcs of approximately 10 mV/m and 100 mV/m, respectively. The large-amplitude ion cyclotron waves also produce a ponderomotive force and a self-consistent ambipolar electric field. Energy considerations show that the downward energy flux in the electromagnetic ion cyclotron wave can be several percent of the total downward auroral electron energy flux. include the inverted V itself [e.g., Frank and Ackerson, 1971; Gumerr, 1972; Lin and Hoffman, 1982], the detailed electron and ion distributions which include upfiowing ion beams and electrons trapped between the potential and the mirror point [Evans, 1974; Shelley et al., 1976; Mizera and Fennell, 1977; Croley et al., 1978; Ghielmetti et al., 1978; Cladis and Sharp, 1979; Sharp et al., 1979; Gorney et al., 1981; Mizera et al., 1981a, b], and electrostatic shocks [Mozer et al., 1977, 1980; Hudson and Mozer, 1978; Totbert and Mozer, 1978; Temerin et al., 1981a, 1981b Bennett et al., 1983, Temerin and Mozer, 1984; Redsun et al., 1985]. However, not all features of auroral particle distributions can be explained by such quasi-static electric fields. Outside of inverted Vs, features of auroral particle acceleration such •s field-aligned counterstreaming electrons [Sharp et al., 1980; Collin et al., 1982], conics [Sharp et al., 1977; Klumpar, 1979] and suprathermal electron bursts [Johnstone and Winningham, 1982] are difficult to .explain by quasi-static electric fields. Even the inverted V electron precipitation shows features which cannot easily be explained by quasi-static electric fields. These include the narrowly field-aligned electrons that are seen not only at the edges of inverted Vs [Hoffman and Evans, 1968; O'Brien and Reasoner, 1971; Arnoldy et al., 1974; Totbert and Carlson, 1980; Carlson and McFadden, 1982] but also well within the inverted V [Lin and Hoffman, 1979a, b; Burchet al., 1979]. Another feature of inverted Vs and auroral arcs that is not explained by quasi-static electric fields is the several hertz periodicities that are sometimes seen in association with bright auroral arcs. These have been seen both i...

Spatial-temporal characteristics of flickering aurora as seen by high-speed EMCCD imaging observations

“…A few observations of such high-energy electrons have been reported based on rocket observations [Spiger and Anderson, 1985;McFadden et al, 1987]. In contrast to previous reports considering that the flickering aurora is originated from EMIC waves inside or below the inverted-V acceleration region [e.g., Temerin et al, 1986], Whiter et al [2010] suggested that the high-energy flickering aurora is explained by the resonance interaction between EMIC waves and precipitating electrons above the inverted-V acceleration region.…”

“…are the parallel and perpendicular wave number, and w ci is the ion cyclotron frequency, respectively [Temerin et al, 1986, Sakanoi et al, 2005.…”

“…[6] Sakanoi et al [2005] extended the theory of Temerin et al [1986] and suggested that the interference between two dispersive Alfvén waves (inertial Alfvén waves or EMIC waves) in a resonance cone can explain both the several kilometers scale of flickering structures and their drifting features (hereafter, we refer to as the Temerin-Sakanoi model in this paper). Gustavsson et al [2008] showed the twodimensional calculation based on the Temerin-Sakanoi model, and they indicated that flickering spots with rotating features can also be explained by the interference of three or more EMIC waves propagating with some different angles.…”

“…Temerin et al [1986] and McFadden et al [1987] considered a model in which H + as well as O + EMIC waves were involved in the electron acceleration. McFadden et al [1987] showed that the EMIC model is hard to satisfy accelerating electrons to higher than a few keV using realistic wave amplitudes.…”

“…[5] Temerin et al [1986] proposed that EMIC waves accelerate electrons to produce field-aligned electron bursts (FABs). This theory was supported by a periodic modulation of FABs at a frequency of several hertz detected by the sounding rocket observations [e.g., McFadden et al, 1987].…”