Olga Panasenco

Context. Fast and slow solar wind have distinct properties linked to their solar sources. The Alfvénic slow wind complicates the usual classification by solar-wind speed, especially at intermediate speeds. The Solar Wind Analyzer (SWA) on Solar Orbiter offers unique capabilities to investigate how Alfvénic slow wind differs from classical fast wind, and relates these differences to their solar origins. Aims. In September 2022, Solar Orbiter moved inbound toward the Sun from 0.59 to 0.38 AU, and observed several Alfvénic streams: one fast wind (F), three Alfvénic slow wind intervals (AS1, AS2, AS3), and a moderate fast wind (MF); a non-Alfvénic slow wind (S) interval was included for comparison. We analyzed these streams to highlight their similarities and differences. Methods. We combined plasma parameters from all SWA sensors with magnetic field measurements from the magnetometer (MAG). A spectral analysis of magnetic and velocity fluctuations was used to characterize the Alfvénicity. The magnetic connectivity of each stream to its solar source was examined using potential field source surface extrapolation combined with ballistic backmapping from the spacecraft. Results. Proton velocity distribution functions exhibit anisotropies and field-aligned beams typical of Alfvénic streams, while electron strahl populations become progressively broader and weaker from fast to non-Alfvénic slow wind. Heavy-ion composition shows a similarly ordered transition, where the Alfvénic slow wind displays intermediate charge-state ratios between fast and non-Alfvénic slow wind. Magnetic connectivity analysis associates the fast wind with a large coronal hole, whereas the Alfvénic slow wind intervals connect to open-field regions near pseudostreamers and overexpanded coronal-hole boundaries. Spectral analysis indicates that most Alfvénic streams remain close to energy equipartition despite their different heliocentric distances and bulk speeds. Altogether, these results support the interpretation of Alfvénic slow wind as the low-speed extension of coronal-hole-associated Alfvénic plasma undergoing a distinct acceleration and transport history. Conclusions. The combined SWA observations offer key insights into how turbulence, particle transport, and coronal source conditions jointly shape the evolution of Alfvénic solar wind streams, revealing a coherent transition between fast, Alfvénic slow, and non-Alfvénic slow wind regimes.

The heliospheric current sheet (HCS) is the boundary between open magnetic fields of opposite polarity in the solar wind that connect back to their respective open-flux regions in the corona. The HCS is often described as a disklike sheet warped by the combined effects of the inclination of the magnetic equator on the Sun, solar rotation, and solar wind expansion. The HCS is an extension of the helmet streamer belt—the closed-flux region resulting from the global dipole component of the observed photospheric magnetic field. In the absence of a strong dipole, a dominant quadrupole can result in two separate HCSs. Here we report on a set of idealized, axisymmetric, solar wind simulations designed to study the transition of the single-HCS corona and inner heliosphere into a multiple-HCS configuration, run with the WindPredict-AW PLUTO MHD code. We systematically vary the relative strengths of the dipole and quadrupole contributions to the global field and show this results in the formation of a large-scale, closed-flux pseudostreamer that interacts with the ambient solar wind. We find that when the dipole and quadrupole magnitudes are approximately equal, our model corona can oscillate between a one- and two-HCS configuration on the timescale of days to weeks. We characterize the plasma dynamics of the transition of a global-scale pseudostreamer into a localized, secondary, helmet-streamer belt with its own HCS surrounding a newly opened, opposite-polarity, coronal hole. We discuss the implications of our results for solar cycle evolution and the dynamic coupling of the highly structured corona and inner heliosphere.

The Sun’s surface vibrates in characteristic 5 minute oscillations, known as p -modes, generated by sound waves trapped within the convection zone. Although these oscillations have long been hypothesized to reach into the solar wind, direct in situ evidence has remained elusive, even during previous close encounters by Parker Solar Probe (PSP). Here, we present strong in situ evidence of 5 minute oscillations in the upper solar corona, based on observations from PSP’s three closest perihelia. In two events at 9.9 solar radii ( R _⊙ ), we identify statistically significant (∼6 σ ) 3.1–3.2 mHz peaks in the magnetic field power spectrum, each appearing as a large-amplitude, spherically polarized Alfvénic wave train lasting approximately 35 minutes. These results demonstrate that global solar oscillations can reach the solar wind.

Context. At the end of April 2021, Parker Solar Probe (PSP) was in alignment with Solar Orbiter and one week later with Earth, observing solar wind streams originating from the same region of the Sun. During the first conjunction, PSP was at 0.10 au and Solar Orbiter at 0.89 au while, during the second conjunction with Earth, PSP was at 0.33 au. Aims. During the two conjunctions, PSP, Solar Orbiter and Earth were connected to the same solar source, an open field region in the neighborhood of a pseudostreamer configuration that is a typical source of Alfvénic slow wind streams. This particular orbital configuration allows us to study not only the evolution of Alfvénic turbulence in the slow wind using multi-s/c measurements at different heliocentric distances, but also the magnetic evolution of the solar source region. Methods. In this work, we reconstructed the solar source using a potential field source surface model and performed a spectral analysis by using magnetic field observations and plasma parameters from spacecraft located at different heliocentric distances to characterize solar wind fluctuations. We then investigated the radial evolution of the turbulent energy transfer rate through the Politano-Pouquet law. Results. The open field region identified as the solar source of the different plasma parcels is characterized by a well-developed pseudostreamer configuration with strong non-monotonic expansion of the open magnetic field that gradually decayed one week later. In turn, in situ observations, although showing a general radial evolution of Alfvénicity due to solar wind expansion, may also reflect the changes experienced by the solar source. The radial weakening of the v - b alignment and the predominance of magnetic energy are associated with an increase in the intermittency of the fluctuations at MHD scales, providing insight on the interaction between Alfvénic fluctuations and turbulence in the heliosphere. The energy transfer rate shows a rapid decay as a function of the radial distance, indicating possible fast energy dissipation for the sample analyzed in this work. Conclusions. Results show a strong radial dependence of Alfvénicity, energy equipartition, homogeneities of the fluctuations and turbulent energy transfer, highlighting how both the solar source evolution and the interaction with local inhomogeneities can shape the properties of solar wind turbulence in different points of the heliosphere.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into “patches”. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into ``patches''. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

Coronal pseudostreamer flux systems have a specific magnetic configuration that influences the morphology and evolution of coronal mass ejections (CMEs) from these regions. Here we continue the analysis of the Wyper et al. magnetohydrodynamic simulation of a CME eruption from an idealized pseudostreamer configuration through the construction of synthetic remote-sensing and in situ observational signatures. We examine the pre-eruption and eruption signatures in extreme ultraviolet and white light from the low corona through the extended solar atmosphere. We calculate synthetic observations corresponding to several Parker Solar Probe–like trajectories at ∼10R _⊙ to highlight the fine-scale structure of the CME eruption in synthetic WISPR imagery and the differences between the in situ plasma and field signatures of flank and central CME-encounter trajectories. Finally, we conclude with a discussion of several aspects of our simulation results in the context of interpretation and analysis of current and future Parker Solar Probe data.

Context. It has been recently accepted that the standard classification of the solar wind solely according to flow speed is outdated, and particular interest has been devoted to the study of the origin and evolution of so-called Alfvénic slow solar wind streams and to what extent such streams resemble or differ from fast wind. Aims. In March 2022, Solar Orbiter completed its first nominal phase perihelion passage. During this interval, it observed several Alfvénic streams, allowing for characterization of fluctuations in three slow wind intervals (AS1-AS3) and comparison with a fast wind stream (F) at almost the same heliocentric distance. Methods. This work makes use of Solar Orbiter plasma parameters from the Solar Wind Analyzer (SWA) and magnetic field measurements from the magnetometer (MAG). The magnetic connectivity to the solar sources of selected solar wind intervals was reconstructed using a ballistic extrapolation based on measured solar wind speed down to the (spherical) source surface at 2.5 R_s below which a potential field extrapolation was used to map back to the Sun. The source regions were identified using SDO/AIA observations. A spectral analysis of in situ measured magnetic field and velocity fluctuations was performed to characterize correlations, Alfvénicity, normalized cross-helicity, and residual energy in the frequency domain as well as intermittency of the fluctuations and spectral energy transfer rate estimated via mixed third-order moments. A machine learning technique was used to separate proton core, proton beam, and alpha particles and to study v − b correlations for the different ion populations in order to evaluate the role played by each population in determining the Alfvénic content of solar wind fluctuations. Results. The comparison between fast wind and Alfvénic slow wind intervals highlights the differences between the two solar wind regimes: The fast wind is characterized by larger amplitude fluctuations, and magnetic and velocity fluctuations are closer to equipartition of energy. In fact the Alfvénic slow wind streams appear to be on a spectrum of wind types, with AS1, originating from open field lines neighboring active regions and displaying similarities with the fast wind in terms of fluctuation amplitude and turbulence characteristics, but not with respect to the alpha particles and proton beams. The other two slow streams differed both in their sources as well as plasma characteristics, with AS2 coming from the expansion of a narrow coronal hole corridor and AS3 from a region straddling a pseudostreamer. The latter displayed the coldest and highest density but the slowest stream with the smallest fluctuation amplitude and greatest magnetic energy excess. It also showed the largest scatter in proton beam speeds and the greatest difference in speed between proton beam and alpha particles. Conclusions. This study shows how the old fast–slow solar wind dichotomy, already called into question by the observations of slower Alfvénic solar wind streams, should further be refined, as the Alfvénic slow wind, originating in different solar wind regions, show significant differences in density, temperature, and proton and alpha-particle properties in the inner heliosphere. The observations presented here provide the starting point for a better understanding of the origin and evolution of different solar wind streams as well as the evolving turbulence contained within.

The heliosphere is permeated with highly structured solar wind originating from the Sun. One of the primary science objectives of Parker Solar Probe (PSP) is to determine the structures and dynamics of the plasma and magnetic fields at the sources of the solar wind. However, establishing the connection between in situ measurements and structures and dynamics in the solar atmosphere is challenging: most of the magnetic footpoint mapping techniques have significant uncertainties in the source localization of a plasma parcel observed in situ, and the PSP plasma measurements suffer from a limited field of view. Therefore, it lacks a universal tool to self-contextualize the in situ measurements. Here we develop a novel time series visualization method named Gaussianity Scalogram. Utilizing this method, by analyzing the magnetic magnitude data from both PSP and Ulysses, we successfully identify in situ structures that are possible remnants of solar atmospheric and magnetic structures spanning more than 7 orders of magnitude, from years to seconds, including polar and midlatitude coronal holes, as well as structures compatible with supergranulation, “jetlets” and “picoflares.” Furthermore, computer simulations of Alfvénic turbulence successfully reproduce the Gaussianization of magnetic magnitude, supporting the observed distribution. Building upon these discoveries, the Gaussianity Scalogram can help future studies to reveal the fractal-like fine structures in the solar wind time series from both PSP and a decades-old data archive.