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

Abstract

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 (Hm) 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 Hm 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.