The roles of static and dynamic electric fields in the auroral acceleration region

Abstract

[1] Charged particles and electric fields measured by the Fast Auroral Snapshot satellite (FAST) are being widely interpreted as final vindication of the theory that the electrons responsible for the brightest and most highly structured forms of aurora gain their energy by being accelerated in static electric fields. However, measurements of electrostatic waves from the same satellite also give further impetus to the opposing theory that the electrons are energized by the dynamic electric fields of plasma waves. Consideration of the different capabilities of static and dynamic electric fields leads to a model of the auroral electron acceleration region incorporating acceleration by both types of fields. An experimental test of the model is suggested.

Influence of the ionosphere on the altitude of discrete auroral arcs

“…If the mechanism were entirely an electrostatic potential drop, variations in the Pedersen conductance would have little effect (Ronnmark and Hamrin, 2000). We may conclude that the observations presented here support at least a combination of electrostatic potential and plasma wave propagation (Bryant, 2002). .…”

Auroral electron acceleration induced by Cherenkov damped waves

“…However, after all the discussions Bryant (1994Bryant ( , 1998 still maintains his position that auroral electron acceleration, by double layer, is fundamentally untenable. New material by the same authors, on the same subject, was published (Brayant, 2002) keeping the controversy still alive. In this paper, we address this controversy afresh, due to its paramount importance to the understanding of the auroral dynamics.…”

“…It can be seen, by examining some rocket and satellite observations of particles and waves in auroral plasmas, that the two structures can co-exist (turbulence and dc electric fields), and that it is possible to observe a flux enhancement in these data Lynch et al, 1999), what cannot, of course, be explained by the two models in a separate way. In short, we can say that general auroral acceleration data show that three situations are present in auroras: the acceleration by static electric fields, the acceleration by turbulence or the acceleration by both phenomena, case addressed partially and not fully properly by Brayant (2002).…”

Energy sources of field‐aligned currents: Auroral electron energization

“…Fundamental physics dictates that electron energization must be mediated through the electric field. There is no consensus as to whether this process can be considered as steady (perhaps involving double layers) and an electric potential (as has been used to good effect by Ergun et al [2002a]) or whether equally fundamental physics means no steady energization can be achieved by such a state [ Bryant et al , 1992; Bryant , 1999, 2002]. That both analyses have some merits is recognized by recent attempts to integrate both aspects in a unified model involving time‐dependent stochastic acceleration in addition to a potential electric field.…”

“…That both analyses have some merits is recognized by recent attempts to integrate both aspects in a unified model involving time‐dependent stochastic acceleration in addition to a potential electric field. Janhunen and Olsson [2000] use stochastic acceleration to drive electrons up the potential hill, whereas Bryant [2002] suggests the stochastic acceleration site is at higher altitudes and lies above an isolated potential well. These studies, like most which are motivated by in situ observations, often focus on a segment of the auroral flux tubes and impose a current or voltage generator at the boundaries of the section considered.…”