A Lagrangian-frame technique for investigating plasma turbulence in complex underlying system-scale structures

We present a method to visualize and analyze turbulence within macroscopic flows that feature complex structures not determined by the turbulence itself. We introduce a technique to shift to a Lagrangian frame that captures the macroscopic scales not part of the turbulent cascade. We then study turbulence within this frame that is comoving with the large-scale nonturbulent flow. The method is applied to Particle-in-Cell simulations of astrophysical plasma. Specifically, we use two cases to illustrate the new method. First, we consider a magnetic perturbation in the solar wind interacting with the bow shock, magnetosheath, and magnetopause in the dayside of the Earth. Second, we consider an Earthward flow generated by magnetic reconnection in the magnetotail. In these cases we show how the Lagrangian frame can be used to distinguish turbulent fluctuations from the macroscopic flow structures due to the evolution of the system caused by macroscopic forcing.