Identification of coherent structures in space plasmas: the magnetic helicity-PVI method

Context. Plasma turbulence can be viewed as a magnetic landscape populated by large- and small-scale coherent structures. In this complex network, large helical magnetic tubes might be separated by small-scale magnetic reconnection events (current sheets). However, the identification of these magnetic structures in a continuous stream of data has always been a challenging task. Aims. Here, we present a method that is able to characterize both the large- and small-scale structures of the turbulent solar wind, based on the combined use of a filtered magnetic helicity (H-m) and the partial variance of increments (PVI). Methods. This simple, single-spacecraft technique was first validated via direct numerical simulations of plasma turbulence and then applied to data from the Parker Solar Probe mission. Results. This novel analysis, combining H-m and PVI methods, reveals that a large number of flux tubes populate the solar wind and continuously merge in contact regions where magnetic reconnection and particle acceleration may occur.