The first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert–Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvénic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence.

Switchbacks are sudden, large radial deflections of the solar wind magnetic field, widely revealed in interplanetary space by the Parker Solar Probe. The switchbacks’ formation mechanism and sources are still unresolved, although candidate mechanisms include Alfvénic turbulence, shear-driven Kelvin–Helmholtz instabilities, interchange reconnection, and geometrical effects related to the Parker spiral. This Letter presents observations from the Metis coronagraph on board a Solar Orbiter of a single large propagating S-shaped vortex, interpreted as the first evidence of a switchback in the solar corona. It originated above an active region with the related loop system bounded by open-field regions to the east and west. Observations, modeling, and theory provide strong arguments in favor of the interchange reconnection origin of switchbacks. Metis measurements suggest that the initiation of the switchback may also be an indicator of the origin of slow solar wind.

The properties of Alfvénic solar wind turbulence have been studied for decades using spacecraft measurements. In particular, the observation of spectral anisotropy of magnetic fluctuations has stimulated the development of several phenomenological models, one of the most popular being critical balance. However, the experimental validation of these models is intrinsically difficult because of the one-dimensional nature of the measurements provided by spacecraft instrumentation. In this work, a thorough search is performed in the Wind spacecraft database to extract samples of field-aligned fast solar wind, which allow the precise estimation of the parallel spectral properties of the magnetic fluctuations, and of their intermittency. Hilbert spectral analysis is used, in order to eliminate the possible role of nonstationarity and large-scale structures. Our results indicate that the spectral anisotropy predicted by the critical balance theory is not observed in the selected database, thus questioning the validity of the critical balance in the solar wind turbulence. A stochastic process characterized by a −5/3 spectral scaling, which is not necessarily attributed to usual turbulence, as indicated by the absence of intermittency, is indeed observed in the analyzed data samples.

Parker Solar Probe (PSP) observed a large variety of Alfvénic fluctuations in the fast and slow solar wind flow during its two perihelia. The properties of Alfvénic solar wind turbulence have been studied for decades in the near-Earth environment. A spectral index of −5/3 or −2 for magnetic field fluctuations has been observed using spacecraft measurements, which can be explained by turbulence theories of nearly incompressible magnetohydrodynamics (NI MHD) or critical balance. In this study, a rigorous search of field-aligned solar wind is applied to PSP measurements for the first time, which yields two events in the apparently slow solar wind. The parallel spectra of the magnetic fluctuations in the inertial range show a power law. Probability distributions of the magnetic field show that these events are not contaminated by intermittent structures, which, according to previous studies, are known to modify spectral properties. The results presented here are consistent with spectral predictions from NI MHD theory and further deepen our understanding of the Alfvénic solar wind turbulence near the Sun.

The nature of the solar wind parallel fluctuations is investigated in this Letter by using magnetic helicity to characterize their polarization state at proton scales. Our aim is to assess the role of the proton cyclotron instability as a mechanism for generating ion cyclotron waves (ICWs) in solar wind turbulence. The wave polarization is found to depend strongly on the proton temperature anisotropy and on the power level of magnetic fluctuations at fluid scales. The results indicate a clear link between fluid and kinetic scales in the solar wind turbulence, allowing for a picture in which the resonant dissipation of high-frequency Alfvén waves heats protons in a direction perpendicular to the magnetic field, increasing their temperature anisotropy. The velocity distribution thus becomes unstable to the proton cyclotron instability, which then drives the local generation of ICWs in the solar wind.

The Hg⁰ time series recorded at the Mauna Loa Observatory (MLO) in Hawaii between 2002 and 2009 has been analyzed using Empirical Mode Decomposition. This technique has been used in numerous contexts in order to identify periodical variations in time series data. The periodicities observed in the tropical Pacific sea surface temperature (SST), through the data collected from five buoys, are also observed in Hg⁰ concentrations and the relative humidity measured at the MLO. The lag times in the observed periodicities are related to the position of the buoys with respect to the measurement site. This demonstrates a direct link between climatological phenomena, in this case SST, and measured Hg⁰ and reflects the influence of ocean SST on Hg⁰ evasion. This is the first long‐term experimental evidence of such a direct effect on Hg⁰ evasion from the oceanic surface driven by temperature.