Magnetic perturbations in the events of broadband ELF turbulence observed by FAST

Abstract

Magnetic perturbations in the topside auroral ionosphere observed by the FAST satellite in the events of broadband extra low frequency (BB ELF) turbulence are investigated at frequencies 0.5–8 Hz (scales from 14 km down to 0.9 km). The power‐law scaling and peculiar polarization patterns of the perturbations are highlighted. By comparing with the magnetic fields simulated according to the Chang et al. (2004) scenario of coarse‐graining process development, we demonstrate that the magnetic perturbations observed in the events of the BB ELF turbulence can be reasonably understood in terms of non‐linearly interacting multiscale field‐aligned currents traversed by the spacecraft.

Convective cell generation by kinetic Alfvén wave turbulence in the auroral ionosphere

“…2 In fact, satellite observations in the auroral ionosphere regularly found convective vortex structures that coexist with small-scale turbulence. 27,28,45,46 Our results, together with that from the observations, suggest that nonlinear cross-scale coupling between KAW turbulence and the CCs plays an important role in the evolution of electromagnetic disturbances in the auroral ionosphere. It should be pointed out that numerical solution of the equations for nonlinear KAWs, or Eqs.…”

“…The observed power-law spectra 25,26 are consistent with the predictions of existing KAW turbulence theory. 44 Accordingly, the instability condition (28) can be satisfied in all these regimes, so that large-scale CCs can be excited by KAW turbulence in the auroral ionosphere, and wave energy is transferred from the small-scale regime to the large-scale regime.…”

“…Since in the ionosphere b < m e =m i , one should consider the instability condition (27) or (28). This condition can be written in terms of the perturbed magnetic field energy spectra as @ k ?…”

“…[6][7][8][9][10][11][20][21][22][23][24] In many laboratory and space plasmas, KAW turbulence instead of monochromatic KAWs are found. [25][26][27][28] Such turbulence can also drive lower frequency modes, in particular the zero-frequency CCs. 29,30 To study the interaction between the CCs and the KAW turbulence, it is convenient to use the wave kinetic equation for the generalized KAW action and the hydrodynamic equations for the CCs since their dynamics involve quite different time and space scales.…”

Inverse cascade in the structure of substorm aurora and non-linear dynamics of field-aligned current filaments

“…Fluctuating electric and magnetic fields in the events of BB ULF-ELF perturbations were found to exhibit power law distributions in frequency, scaling properties, nonGaussian probability density functions, and other signatures of the intermittent turbulence (e.g. Temerin, 1978;Kintner et al, 2000;Tam et al, 2005;Parkinson, 2006;Golovchanskaya et al, 2011). The phenomenon of the BBELF turbulence occurs at all local times (most frequently in the prenoon sector), for any dipole tilt, in a wide variety of solar wind and geomagnetic conditions (Matsuo et al, 2003;Heppner et al, 1993).…”