A Perspective on the Scaling of Magnetosheath Turbulence and Effects of Bow Shock Properties

Abstract

We analyze magnetic field data from two magnetosheath crossings, representative of a larger collection of similar cases in the database of the Cluster spacecraft. We apply a novel data analysis method to identify the power-law behavior of the structure functions and to find the validity range of the power-law scaling. We validate the technique with solar wind magnetic field data and a synthetic magnetic field signal. This approach grants a rigorous determination of the scale range for a linear fit of the structure function in the log–log representation, which most often is chosen arbitrarily. The fitting allows an estimation of the power spectral index from the scale variation of the second-order structure function exponent. Data recorded during the first Cluster magnetosheath crossing, called Event 1, indicate three different power-law scaling regimes (injection, inertial, and kinetic) separated by two spectral breaks, consistent with the scenario of fully developed turbulence. However, data from the second Cluster magnetosheath crossing, called Event 2, depict a different scenario with only two power-law scaling regimes determined from the fit. A spectral slope shallower than the Kolmogorovian solar wind power-law index is determined at magnetohydrodynamic scales, spanning more than three frequency decades, which is separated by a spectral break from the kinetic regime. An analysis of simultaneous solar wind data from the Advanced Composition Explorer suggests that the scale behavior of the magnetosheath fluctuations might be controlled by the structure of the bow shock; solar wind turbulent fluctuations are only partially destroyed while they are carried across the bow shock. Both events are recorded in a quasi-perpendicular magnetosheath.

Cross-helicity and transition from magnetohydrodynamics to kinetics in space plasmas

“…5a of the Ref. [28]. For this case the mean velocity of the plasma | V | (in the spacecraft frame) was significantly larger than the representative fluctuations of the velocity.…”

“…In a recent paper Ref. [28] the magnetic energy spectrum was calculated using the data obtained by the Cluster Fluxgate Magnetometer onboard the Cluster spacecraft operated in the Earth's magnetosheath under slow solar wind conditions. The magnetosheath magnetic field was, for the most part of the measurements, perpendicular to the mean flow direction.…”

Scale‐Dependent Kurtosis of Magnetic Field Fluctuations in the Solar Wind: A Multi‐Scale Study With Cluster 2003–2015

“…The observed differences are likely due to the different methods of calculating the mean‐field and to a limitation of the two‐point structure‐function in measuring steep spectra (Abry et al., 1995;Chen, Horbury, et al., 2010; Chen, Wicks, et al., 2010; Landi et al., 2019; Monin et al., 1975; Teodorescu et al., 2021). To overcome this limitation, three or five point structure functions could be calculated (e.g., Cho et al., 2019; Landi et al., 2019; Teodorescu et al., 2021; Wang et al., 2020). As we only have two spacecraft to calculate spatial lags, we restrict the analysis to two‐point structure functions to enable comparison between temporal and spatial lags.…”

“…Table 2 gives the spectral indices obtained from (a) second order structure functions in the local mean field frame, Figure 5, and (b) the wavelet spectra calculated in the global field frame. The observed differences are likely due to the different methods of calculating the mean‐field and to a limitation of the two‐point structure‐function in measuring steep spectra (Abry et al., 1995;Chen, Horbury, et al., 2010; Chen, Wicks, et al., 2010; Landi et al., 2019; Monin et al., 1975; Teodorescu et al., 2021). To overcome this limitation, three or five point structure functions could be calculated (e.g., Cho et al., 2019; Landi et al., 2019; Teodorescu et al., 2021; Wang et al., 2020).…”

On the phenomenology of magnetosheath jets with insight from theory, modelling, numerical simulations and observations by Cluster spacecraft

“…Other approaches considered mapping to the bow-shock along magnetosheath streamlines (Karlson et al, 2018). More details on the procedure applied to determine the normal direction to the model bow shock and model magnetopause can be found in Teodorescu et al (2021). Note that the data needed to compute D MP and D BS were available for a subset of 850 jets, illustrated in Figure 3 where we show their positions in the (X,R YZ ) GSE plane, where R YZ Y 2 + Z 2 √ .…”