Vladimir Krasnosselskikh

The collisionless shock research started in the late 1950s. Since then, plenty of data have been accumulated due to the large number of missions in the heliosphere, providing in situ measurements of the fields and particles. The quality of these measurements has vastly improved, especially in the last two decades. Much more data is available for analysis than is already analyzed. Theoretical studies received a push in 1966, when it was shown that shocks are formed due to the interplay between the nonlinear steepening and dispersive broadening of the magnetic field profile. At present, it is a common point of view that shocks are essentially shaped by the kinetics of ions. So far, we achieved a good semi‐quantitative understanding of the ion heating in low‐Mach number shocks and the relation of this process to the magnetic profile, and a qualitative understanding of the ion reflection and the nature of the well‐structured magnetic field. Rippled and nonstationary quasi‐perpendicular shocks have been observed, and theory is being developed.

Solar radio bursts, and astrophysical radio emissions in general, are observed either in space or on the ground by measuring their fluctuating electric field. Here, we report the first measurement of the magnetic component of a solar radio wave, observed simultaneously by the Solar Orbiter and Parker Solar Probe missions. The observations were made during the type III radio burst on 2021 October 28. The analysis of the wave polarization and magnetic and electric field amplitudes allows us to estimate the refractive index and put constraints on the direction of the wave. The wave is found to be consistent with an ordinary-mode wave and with a source near the southeast limb of the Sun. These results pave the way for future observations and analyses of the magnetic field of radio waves, in particular, for solar radio bursts.

The magnetic field in the chromosphere and low corona near the boundaries of equatorial coronal holes in the quiet Sun is thought to reconfigure through interchange reconnection (IR). This process occurs in low-beta plasma with a strong guiding field and may produce an ion distributions known as “hammerhead.” These distributions have been observed in coronal plasma associated with current sheets and in regions whose footpoints lie near equatorial coronal holes. They usually consist of a core plus a perpendicularly diffuse beam feature at a specific velocity relative to the core. The mechanism we propose involves the interpenetration of two plasmas with different properties—one on closed field lines and one on open field lines. In the chromosphere and low corona, these distributions can generate ion-sound and ion-cyclotron waves once the beam’s relative velocity exceeds a threshold. As such plasma distributions travel toward the solar wind through a funnel region where the magnetic field and plasma density rapidly drop, they may become unstable and produce Alfvén-type magnetic perturbations that can evolve nonlinearly into switchback structures. These threshold conditions are likely met near the transition from sub-Alfvénic to super-Alfvénic wind.

Collisionless shocks are often modelled as smooth, planar surfaces - but many show organized corrugations that steer how particles get accelerated and how they radiate. We present a simple, linear magnetohydrodynamic (MHD) model that treats the shock as an evolving interface. This lets us separate two things: (1) the shock’s own properties and geometry, and (2) the statistics of the upstream turbulence that hits it. With this separation, we obtain adirect map from incoming fluctuations to the corrugation patterns they create, including their drift speed and coherence. In our model, the interface acts like an “impedance” that focuses broad-band turbulent power into fast-mode waves that skim along the shock. The shock responds most strongly when the wave’s normal group speed is small (a sharp, single-peaked response). Corrugation strength increases with compression, while the shock geometry and plasma beta control how long these patterns persist. The framework makes testable predictions linking upstream turbulence and shock shape to finestructure in electromagnetic signals from heliospheric and supernova-remnant shocks.

The formation of a collisionless shock is the result of a balance between nonlinear steepening and processes that counteract this steepening. Dispersive shocks are shocks in which dispersive processes counterbalance the front steepening and are formed when the dispersive spatial scale exceeds scales associated with resistive processes. Oblique dispersive shocks are characterized by a phase standing wave precursor adjacent to the magnetic ramp. The whistler critical Mach number is defined as the maximum Mach number for which a linear whistler wave can phase stand upstream of the shock front. It was widely accepted that if the Mach number exceeds , linear whistler waves propagating along the shock normal are not able to “phase stand” in the upstream flow, and “…the shock will be initiated by a monotonic ramp.” (Kennel et al., 1985, https://doi.org/10.1029/gm034p0001 ). In this study, we present results of numerical simulations and observations of shocks with that reveal the occurrence of an alternative scenario. For both the shock resulting from kinetic particle‐in‐cell simulations and that observed by MMS, the propagation direction of the precursor deviates from the shock normal direction. As a result, the velocity of the surface of constant phase along the shock normal exceeds the phase speed of these waves. It is shown that the propagation of the surface of constant phase along the shock normal occurs at a velocity that is nearly equal to the shock speed. Hence, these waves are “phase standing along the shock normal” in spite of .

Type III radio bursts are signatures of the fluxes of near-relativistic electrons ejected during solar flares. These bursts are frequently observed by spacecraft such as the Parker Solar Probe. It has been traditionally believed that these electron beams generate Langmuir waves through the two-stream instability, which are then converted into electromagnetic waves. In this study, we revise that model, by examining how the electron distribution becomes truncated due to the “time-of-flight” effect, as the beam travels through a randomly inhomogeneous and gently varying solar wind plasma. Rather than the two-stream instability, this truncation destabilizes the distribution and leads to the generation of Langmuir waves via a linear instability; we confine our analysis to this linear regime and do not take into account the backreaction of the generated Langmuir waves on the electron distribution, which is nonlinear. The instability grows until slower electrons arrive and dampen the waves. Our qualitative analysis shows that the resulting wave intensity growth and decay closely match the intensity–time profile of observed type III radio bursts at the fundamental frequency, supporting this modified theory.

Context. In situ studies of the solar wind require precise magnetic field measurements at all frequencies. The Solar Orbiter mission carries two magnetometers to measure the solar wind magnetic field: the fluxgate magnetometer (MAG), which is best suited for frequencies from DC to a few Hertz, and the search coil magnetometer (SCM), which is best suited for frequencies above a few Hertz. Aims. The aim of this paper is to produce a merged magnetic field data product that takes the best of both instruments and provides the community with high quality, easy to use magnetic field data over a wide range of frequencies. Methods. We first compared the two instruments in their overlapping frequency range, then we performed the merging in Fourier space using a weighted function determined by the sensitivity of the two sensors. Results. The two instruments are found to give consistent results in their overlapping frequency range. SCM has a lower gain than MAG by 14% around 1 Hz and MAG is delayed by about 20 ms with respect to SCM, and the merged magnetic field takes care of these discrepancies. It is basically identical to MAG data below 2 Hz and to SCM data above about 15 Hz (with amplitude increased by 14%). We show that the merged magnetic field is suitable to analyse waves and turbulence over a broad frequency range, in particular by confirming that ion cyclotron waves can lower the level of energy at the sub ionic scales. The merged magnetic field is distributed as daily files containing the magnetic field at either 256 or 4096 Hz, and either in the radial-tangential-normal co-ordinates or in the spacecraft reference frame co-ordinates.

We present statistics on the polarization properties of whistler waves in the solar wind down to 0.05 AU (10.75 RS) using data from Parker Solar Probe's first 17 encounters. These properties were previously uncharacterized due to a technical issue affecting one component of the search‐coil magnetometer after Encounter 1. Using a reconstruction technique, we show that whistlers are predominantly quasi‐parallel to the magnetic field across all distances and propagation directions, with 87% exhibiting a propagation angle relative to the background magnetic field below 25. Waves with above 25 are observed with significantly lower amplitudes. Sunward whistlers (including counter‐propagating (CP) cases, where anti‐sunward waves are observed at the same time) statistically exhibit higher normalized amplitudes and frequencies than anti‐sunward whistlers. We discuss generation mechanisms and wave‐particle interactions. Specifically, CP sunward and sunward waves interact via less efficient resonances with Strahl electrons ( eV).

Low Mach number, fast magnetosonic, dispersive shocks are formed if the characteristic scale of the shock front exceeds the characteristic the spatial scale associated with resistive processes. In these cases, dispersion arrests the nonlinear steepening of the shock front. According to the established view, a whistler wave precursor, whose wave vector is parallel to the shock normal, is formed in oblique dispersive shocks provided that the Mach number does not exceed the Whistler Critical Mach number Mw. Numerical simulations and data obtained by the MMS satellites are used to investigate the evolution of the properties of the upstream whistler precursor as the Mach number increases above Mw.