Abstract
Abstract The power spectral density of magnetic fluctuations in the solar wind exhibits several power-law-like frequency ranges with a well-defined break between approximately 0.1 and 1 Hz in the spacecraft frame. The exact dependence of this break scale on solar wind parameters has been extensively studied but is not yet fully understood. Recent studies have suggested that reconnection may induce a break in the spectrum at a “disruption scale” , which may be larger than the fundamental ion kinetic scales, producing an unusually steep spectrum just below the break. We present a statistical investigation of the dependence of the break scale on the proton gyroradius ρ i , ion inertial length d i , ion sound radius ρ s , proton–cyclotron resonance scale ρ c , and disruption scale as a function of . We find that the steepest spectral indices of the dissipation range occur when β e is in the range of 0.1–1 and the break scale is only slightly larger than the ion sound scale (a situation occurring 41% of the time at 1 au), in qualitative agreement with the reconnection model. In this range, the break scale shows a remarkably good correlation with . Our findings suggest that, at least at low β e , reconnection may play an important role in the development of the dissipation range turbulent cascade and cause unusually steep (steeper than −3) spectral indices.
Highlights
Plasma in the solar wind exhibits a turbulent cascade over a very wide range of scales (Chen 2016)
The turbulent power spectrum consists of several power-law-like ranges, in which different physical mechanisms are involved in the transfer of energy to smaller scales
The power spectrum of magnetic fluctuations in this range is generally close to E (k^) μ k^-5 3 (e.g., Matthaeus & Goldstein 1982; Chen et al 2011)
Summary
Plasma in the solar wind exhibits a turbulent cascade over a very wide range of scales (Chen 2016). The ion kinetic break scale lB, in the so-called “dissipation range,” the turbulent spectrum steepens—generally the spectral index is approximately −2.8 or steeper in this range (below lB but above a second break or exponential cutoff at electron kinetic scales; Alexandrova et al 2009; Sahraoui et al 2010). This steepening of the spectrum has been explained (Schekochihin et al 2009; Howes et al 2011; Boldyrev & Perez 2012) by the fact that below the characteristic ion kinetic scales, the dispersion relation of the characteristic fluctuations of the plasma changes.
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