Using high-resolution Cluster satellite observations and a multi-dimensional intermittency technique, we show that the magnetic discontinuities in the turbulent solar wind are connected through the spatial scales, going from proton down to electron scales. In some circumstances, their structure resembles the Harris equilibrium profile in plasmas. Observations are consistent with a scenario where many current layers develop in turbulence and where the outflow of these reconnection events are characterized by complex sub-proton networks of secondary islands, in a self-similar way. Although in the past these pictures have been speculated to be separately ubiquitous, through theories and simulations, the present work confirms that “reconnection in turbulence” and “turbulent reconnection” coexist in space plasmas.

Recent accumulation of a critical mass of observational material from different spacecraft complete with the enhanced abilities of numerical methods have led to a boom of studies revealing the high complexity of processes occurring in the heliosphere. Views on the solar wind filling the interplanetary medium have dramatically developed from the beginning of the space era. A 2-D picture of the freely expanding solar corona and non-interacting solar wind structures described as planar or spherically-symmetric objects has dominated for decades. Meanwhile, the scientific community gradually moved to a modern understanding of the importance of the 3-D nature of heliospheric processes and their studies via MHD/kinetic simulations, as well as observations of large-scale flows and streams both in situ and remotely, in white light and/or via interplanetary scintillations. The new 3-D approach has provided an opportunity to understand the dynamics of heliospheric structures and processes that could not even be imagined before within the 2-D paradigm. In this review, we highlight a piece of the puzzle, showing the evolution of views on processes related to current sheets, plasmoids, blobs and flux ropes of various scales and origins in the heliosphere. The first part of the review focuses on introducing these plasma structures, discussing their key properties, and paying special attention to their observations in different space plasmas.

The subject of switchbacks, defined either as large angular deflections or polarity reversals of the magnetic field, has generated substantial interest in the space physics community since the launch of the Parker Solar Probe (PSP) in 2018. Previous studies have characterized switchbacks in several different ways and have been restricted to data available from the first few orbits. Here, we analyze the frequency of occurrence of switchbacks per unit distance for the first full eight orbits of PSP. In this work, events that reverse the sign of the magnetic field relative to a regional average are considered switchbacks. A significant finding is that the rate of occurrence falls off sharply approaching the Sun near 0.2 au (40 R _⊙) and rises gently from 0.2 au outward. The analysis is varied for different magnetic field cadences and for different local averages of the ambient field, confirming the robustness of the results. We discuss implications for the mechanisms of switchback generation. A publicly available database has been created with the identified reversals.

Recent studies of particle acceleration in the heliosphere have revealed a new mechanism that can locally energize particles up to several MeV nucleon^–1. Stream–stream interactions, as well as the heliospheric current sheet (CS)—stream interactions, lead to formation of large magnetic cavities, bordered by strong CSs, which in turn produce secondary CSs and dynamical small-scale magnetic islands (SMIs) of ∼0.01 au or less owing to magnetic reconnection. It has been shown that particle acceleration or reacceleration occurs via stochastic magnetic reconnection in dynamical SMIs confined inside magnetic cavities observed at 1 au. The study links the occurrence of CSs and SMIs with characteristics of intermittent turbulence and observations of energetic particles of keV–MeV nucleon^–1 energies at ∼5.3 au. We analyze selected samples of different plasmas observed by Ulysses during a widely discussed event, which was characterized by a series of high-speed streams of various origins that interacted beyond Earth’s orbit in 2005 January. The interactions formed complex conglomerates of merged interplanetary coronal mass ejections, stream/corotating interaction regions, and magnetic cavities. We study properties of turbulence and associated structures of various scales. We confirm the importance of intermittent turbulence and magnetic reconnection in modulating solar energetic particle flux and even local particle acceleration. Coherent structures, including CSs and SMIs, play a significant role in the development of secondary stochastic particle acceleration, which changes the observed energetic particle flux time–intensity profiles and increases the final energy level to which energetic particles can be accelerated in the solar wind.