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We statistically examine the characteristic scaling features of fluctuations in the dayside Venusian magnetosheath downstream of different types, quasi‐parallel (Q∥) and quasi‐perpendicular (Q⊥), of bow shock based on Venus Express data. We found that magnetic fluctuations have different characteristic scaling features downstream of Q∥ and Q⊥ bow shocks. Although the Venusian dayside magnetosheath is much thinner than the Earth magnetosheath, fully developed turbulence can be still observed downstream of the Q∥ bow shock, while the turbulence is not dominant downstream of Q⊥ bow shock. The type of bow shock plays an important role in the characteristic scaling features of downstream magnetic fluctuations. That means that the Q∥ IMF might be a source of the turbulence in Venusian magnetosheath. Key Points: Magnetic fluctuations have different characteristic scaling features downstream of Q∥ and Q⊥ bow shocksFully developed turbulence can be observed downstream of the Q∥ bow shock, while the turbulence is not dominant downstream of Q⊥ bow shockThe Q⊥ IMF might be a source of the turbulence in Venusian magnetosheath [ABSTRACT FROM AUTHOR]

Context. Tangential velocity discontinuity near the boundaries of solar wind magnetic flux tubes results in Kelvin-Helmholtz instability, which might contribute to solar wind turbulence. While the axial magnetic field stabilizes the instability, a small twist in the magnetic field may allow sub-Alfvénic motions to be unstable. Aims. We aim to study the Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind with different configurations of the external magnetic field. Methods. We use magnetohydrodynamic equations in cylindrical geometry and derive the dispersion equations governing the dynamics of twisted magnetic flux tubes moving along its axis in the cases of untwisted and twisted external fields. Then, we solve the dispersion equations analytically and numerically and find thresholds for Kelvin-Helmholtz instability in both cases of the external field. Results. Both analytical and numerical solutions show that the Kelvin-Helmholtz instability is suppressed in the twisted tube by the external axial magnetic field for sub-Alfvénic motions. However, even a small twist in the external magnetic field allows the Kelvin-Helmholtz instability to be developed for any sub-Alfvénic motion. The unstable harmonics correspond to vortices with high azimuthal mode numbers that are carried by the flow. Conclusions. Twisted magnetic flux tubes can be unstable to Kelvin-Helmholtz instability when they move with small speed relative to the main solar wind stream, then the Kelvin-Helmholtz vortices may significantly contribute to the solar wind turbulence. [ABSTRACT FROM AUTHOR]

Bursty bulk flow associated magnetic fluctuations exhibit at least three spectral scaling ranges in the Earth's plasma sheet. Two of the three scaling ranges can be associated with multi-scale magnetohydrodynamic turbulence between the spatial scales from ~100 km to several RE (RE is the Earth's radius). These scales include the inertial range and below ~0.5RE a steepened scaling range, theoretically not fully understood yet. It is shown that, in the near-Earth plasma sheet, the inertial range can be robustly identified only if multi-scale quasi stationary (MSQS) data intervals are selected. Multiple bursty flow associated magnetic fluctuations, however, exhibit 1/f type scaling indicating that large-scale fluctuations are controlled by multiple uncorrelated driving sources of the bulk flows (e.g. magnetic reconnection, instabilities). [ABSTRACT FROM AUTHOR]

During the last several years significant progress has been made in understanding MHD turbulence in the Earth’s plasma sheet. Due to the statistically transitory properties of fluctuations, finite size and boundary effects, however, issues of fundamental importance remain unresolved. Here we concentrate on such intrinsic features of plasma sheet turbulence as its origin and dynamical nature. In particular, we investigate bursty bulk flow driven multi-scale transfer of energy towards the dissipation scale, and provide evidence for the presence of non-linear interactions. We show that, in contrast with previous results, Alfvénic fluctuations together with 2D eddy interactions may appear as important constituents of turbulence in the plasma sheet. [ABSTRACT FROM AUTHOR]