Ubiquitous threshold for coherent structures in the kinetic and inertial ranges of solar wind turbulence from Solar Orbiter observations

Solar Orbiter observations provide an unprecedented opportunity to study plasma turbulence in the solar wind. On magnetohydrodynamic scales intermittent structures mediate the cascade, due to non-linear wave-wave interactions and coherent structures. Those coherent structures are often quantified and identified by the Partial Variance Increment (PVI).

We obtain magnetic field fluctuations from observations of homogeneous turbulence by wavelet decompositions which preferentially resolve either signatures of coherent structures or wave-packets. Comparing the PVI obtained from both wavelet decompositions, this provides a new, physics based method to determine the PVI threshold above which fluctuations may be coherent structures.

We find a single PVI threshold in each of the kinetic and inertial ranges above which coherent structures typically dominate. This threshold is insensitive to the plasma conditions or heliocentric distance. Therefore, it suggests a ubiquitous constraint on the turbulent phenomenology. This can inform estimates of the heating rates of the solar wind due to the turbulence.