Abstract
Abstract. In the auroral kilometric radiation (AKR) source region, acceleration layers narrow in altitude and associated with parallel field-aligned potential drops of several kV can be identified by using both particles and wave-field high time-resolution measurements from the Fast Auroral SnapshoT explorer spacecraft (FAST). These so-called double layers (DLs) are recorded around density enhancements in the auroral cavity, where the enhancement can be at the edge of the cavity or even within the cavity at a small scale. Once immersed in the plasma, DLs necessarily accelerate particles along the magnetic field lines, thereby generating locally strong turbulent processes leading to the formation of nonlinear phase space holes. The FAST data reveal the asymmetric character of the turbulence: the regions located on the high-potential side of the DLs are characterized by the presence of electron holes, while on the low-potential side, ion holes are recorded. The existence of these nonlinear phase space holes may affect the AKR radiation pattern in the neighbourhood of a DL where the electron distribution function is drastically different from a horseshoe shape. We present some observations which illustrate the systematic generation of elementary radiation events occurring significantly above the local electron gyrofrequency in the presence of electron holes. These fine-scale AKR radiators are associated with a local electron distribution which presents a pronounced beam-like shape.
Highlights
The present communication is devoted to the study of some strong turbulent processes taking place in the Earth’s auroral region in connection with particle acceleration and radiation generation
The Fast Auroral SnapshoT explorer spacecraft (FAST) observations have demonstrated unambiguously that parallel potential drops, supported by nonlinear features identified as double layers (DLs), constitute the source of auroral particle acceleration (Carlson et al, 1998)
In the present paper we focus on the analysis of the FAST data obtained in the region located on the highpotential side of a DL
Summary
The present communication is devoted to the study of some strong turbulent processes taking place in the Earth’s auroral region in connection with particle acceleration and radiation generation. These AKR emissions occur at frequencies 20 % above the local electron gyrofrequency (fce ∼ 360 kHz) and exhibit no apparent polarization in a direction perpendicular to the magnetic field Several distinct regions with large positive parallel velocity gradients can be identified from v// ∼ 3.5 × 104 km s−1 to v// ∼ 5 × 104 km s−1 This implies that, during the measuring time of the electron distribution function, FAST is crossing a local parallel electric field directed anti-earthward which accelerates the electrons from ∼ 7 to ∼ 14 keV. Some parts of the arguments advanced in this theory provide some clues that EHs could contribute to the generation of radiation
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