Magnetic Turbulence in the Geospace Environment

Abstract

Magnetic turbulence is found in most space plasmas, including the Earth's magnetosphere, and the interaction region between the magnetosphere and the solar wind. Recent spacecraft observations of magnetic turbulence in the ion foreshock, in the magnetosheath, in the polar cusp regions, in the magnetotail, and in the high latitude ionosphere are reviewed. It is found that: 1. A large share of magnetic turbulence in the geospace environment is generated locally, as due for instance to the reflected ion beams in the ion foreshock, to temperature anisotropy in the magnetosheath and the polar cusp regions, to velocity shear in the magnetosheath and magnetotail, and to magnetic reconnection at the magnetopause and in the magnetotail. 2. Spectral indices close to the Kolmogorov value can be recovered for low frequency turbulence when long enough intervals at relatively constant flow speed are analyzed in the magnetotail, or when fluctuations in the magnetosheath are G. Zimbardo et al. considered far downstream from the bow shock. 3. For high frequency turbulence, a spectral index α 2.3 or larger is observed in most geospace regions, in agreement with what is observed in the solar wind. 4. More studies are needed to gain an understanding of turbulence dissipation in the geospace environment, also keeping in mind that the strong temperature anisotropies which are observed show that wave particle interactions can be a source of wave emission rather than of turbulence dissipation. 5. Several spacecraft observations show the existence of vortices in the magnetosheath, on the magnetopause, in the magnetotail, and in the ionosphere, so that they may have a primary role in the turbulent injection and evolution. The influence of such a turbulence on the plasma transport, dynamics, and energization will be described, also using the results of numerical simulations.

Fast Magnetic Reconnection and Spontaneous Stochasticity

“…Like nearly every cosmic plasma, the magnetosphere commonly exhibits turbulence, either statistically steady or in sporadic bursts (Zimbardo et al 2010). Energy spectra are generally similar to those in the solar wind, with spectral exponents close to −5/3 and −7/3 at scales above and below the ion gyroradius/ ion skin depth (since β 0.1-10, these are nearly the same), respectively (see Table 1 in Zimbardo et al 2010). The relation between observed turbulence in the magnetosphere and enhanced reconnection speeds is still under debate in the literature (Eastwood et al 2009).…”

“…b Bemporad et al (2008). c Zimbardo et al (2010). , assuming GS95 turbulence holds down to that scale (see Equation (72)), and should not be taken literally when ⊥ η < ρ i .…”

Electric and magnetic spectra from MHD to electron scales in the magnetosheath

“…Spectra of the magnetic field from MHD to sub-ion scales in the magnetosheath have been reported by Alexandrova, Lacombe & Mangeney (2008a) using the Cluster spacecraft, and on kinetic scales by e.g. Sundkvist et al (2007) and Huang et al (2014); see also Zimbardo et al (2010) for a review on magnetic turbulence in this region. Properties of electric and magnetic spectra between ion and electron scales have been previously studied by Mangeney et al (2006) and Lacombe et al (2006), confirming that this regime can be well resolved in the magnetosheath using Cluster.…”

Proton and heavy ion acceleration by stochastic fluctuations in the Earth's magnetotail

“…Spacecraft observations suggest that both electrons and ions are accelerated not only in the vicinity of the reconnection X line but also in a larger area around the reconnection region (e.g., Imada et al, 2007;Grigorenko et al, 2009;Ono et al, 2009). Indeed, during disturbed periods, strong electric (Cattel and Mozer, 1982), velocity and magnetic fluctuations (e.g., Hoshino et al, 1994;Borovsky et al, 1997;Zimbardo et al, 2010), as well as energetic ions, are observed in the magnetotail.…”