arXiv subjects

Andrii Voshchepynets

Publications and source records attributed to Andrii Voshchepynets.

7 recordsLinked to original sources

arXiv2026

On flying near the base of a pseudo-streamer

Near the 10 solar radius perihelion of Parker Solar Probe encounter 24, a confined region containing an enhanced plasma density (25,000 per cubic centimeter) and broadband electrostatic waves was encountered. The solar wind velocity (200 kilometers per second) and ion temperature (25 electron Volts) were significantly reduced as compared to their values in the ambient solar wind. Because the polarity of the radial magnetic field did not change sign on the two sides of the crossing and the crossed region contained a double-peaked plasma structure, the spacecraft must have passed near the base of a pseudo-streamer. In the plasma frame, an electric field as large as 400 millivolts per meter was detected during the crossing. This field is not associated with an ExB drift because it is observed in the plasma rest frame. Instead, it is balanced by the Generalized Ohm's Law terms whose current dependent term associated with this electric field was less than 1 milliampere per square meter, corresponding to a drift velocity less than 2.5 kilometers per second. The region also contained a turbulent plasma with density fluctuations as large as 0.3, suggesting that the resistive term in the Generalized Ohm's Law could be significant. In addition, both the density and electric field had non-zero slopes as functions of time, suggesting that the pressure gradient term in the Generalized Ohm's Law also mattered. This large electric field in the plasma rest frame may be the first and largest such field ever reported.

physics.space-ph↗

arXiv2025

On the origin of the dominant waves in the extended solar corona

The extended solar corona at 10-30 solar radii is essentially devoid of all waves below 100 kHz other than triggered ion acoustic waves (TIAW), which consist of a low frequency electromagnetic wave at a frequency of a few Hz coupled to one or more electrostatic waves at a few hundred Hz, such that the amplitudes of the higher frequency waves peak at a fixed phase of each low frequency wave period. All the waves in a TIAW event travel at the same phase speed, which is found to be 150 km/sec (the ion acoustic speed was about 100 km/sec). It has not been possible to explain the TIAW as a resonant wave-wave interaction, so a non-resonant interaction has been considered in which the loss of energy by the low frequency wave is used to both heat the electrons and grow the higher frequency waves. Evidence in support of this explanation is described and a PIC simulation that discusses this process is summarized. This simulation demonstrates wave-particle interactions driven by the enhanced LF fluctuations, which subsequently modify the proton VDF and create conditions favorable for the growth of HF waves. This interplay between a pair of waves, mediated by modifications of plasma parameters and energy conversion, represents a significant nonlinear process in plasma physics, the study of which will deepen the understanding of energy transfer, wave generation, and plasma dynamics in diverse astrophysical environments.

astro-ph.SR↗

arXiv2025

Intermingled open and closed magnetic field lines near the radial origin of the heliospheric current sheet

Aims. To investigate the magnetic field geometry and waves in the region near the Sun where the heliospheric current sheet is formed. Methods. One good example of apparent open and closed field lines was found and its fields and plasmas were analyzed. Results. The radial component of the magnetic field (the Z-component) measured on the Parker Solar Probe (PSP) changed sign between 12:00 and 13:00 UT on March 30, 2024, when the spacecraft was at 13 solar radii. This sign change may have occurred because the spacecraft crossed the heliospheric current sheet on long open magnetic field lines or it may have occurred because the spacecraft crossed from one side of the equator to the other on much shorter closed magnetic field lines. During this crossing, two distinct regions having different magnetic field geometries, strahl flows, plasma densities, and electric field spectra were observed and identified as regions with open and closed magnetic field lines, respectively. The two regions intermingled on time scales less than 100 milliseconds to create a complex magnetic field geometry. The waves observed in both regions were electrostatic and composed of wide band signatures (in the open field lines regions) and well-structured frequency harmonics (in both the open and closed field lines regions). These harmonic frequencies correlated with the proton plasma frequency, fpp, with the lowest frequency at ~0.1fpp. This result plus the field aligned electric field perturbations and plasma density fluctuations, require that the observed intense electrostatic mode and associated harmonics were ion acoustic waves. The absence of broadband electrostatic signals in closed field line regions is explained by the lower (than in open field line regions) hot and core electron density and higher ratio of the electron plasma frequency to the electron gyrofrequency, suppressing wave generation.

astro-ph.SR↗

arXiv2024

On the origin of the type-III radiation observed near the Sun

$\textit{AIMS.}$ To investigate processes associated with generation of type-III radiation. $\textit{METHODS.}$ Measure the amplitudes and phase velocities of Parker Solar Probe observed electric fields, magnetic fields, and plasma density fluctuations. $\textit{RESULTS.}$ (1) There are slow electrostatic waves near the Langmuir frequency and at as many as six harmonics, the number of which increases with the amplitude of the Langmuir wave. Their electrostatic nature is shown by measurement of the plasma density fluctuations. From these density fluctuations and the electric field magnitude, the k-value of the Langmuir wave is estimated to be 0.14 and $k λ_d$ = 0.4. Even with a large uncertainty in this quantity (more than a factor of two) the phase velocity of the Langmuir wave was <10,000 km/sec. (2) There is an electromagnetic wave near the Langmuir frequency having a phase velocity <50,000 km/sec. (3) Whether there are electromagnetic waves at the harmonics of the Langmuir frequency cannot be determined because, if they existed, their magnetic field components would be below the noise level of the measurement. (4) The rapid (less than one msec) amplitude variations typical of the Langmuir wave and its harmonics are artifacts resulting from addition of two waves, one of which has small frequency variations that arise from traveling through density irregularities. None of these results are expected in or consistent with the conventional model of the three-wave interaction of two counter-streaming Langmuir waves that coalesce to produce the type-III wave. They are consistent with a new model in which electrostatic antenna waves are produced at the harmonics by radiation of the Langmuir wave, after which at least the first harmonic wave evolved through density irregularities such that its wave number decreased and it became the type-III radiation.

astro-ph.SR↗

arXiv2023

Multi-Point Detection of the Powerful Gamma Ray Burst GRB221009A Propagation through the Heliosphere on October 9, 2022

We present the results of processing the effects of the powerful Gamma Ray Burst GRB221009A captured by the charged particle detectors (electrostatic analyzers and solid-state detectors) onboard spacecraft at different points in the heliosphere on October 9, 2022. To follow the GRB221009A propagation through the heliosphere we used the electron and proton flux measurements from solar missions Solar Orbiter and STEREO-A; Earth magnetosphere and the solar wind missions THEMIS and Wind; meteorological satellites POES15, POES19, MetOp3; and MAVEN - a NASA mission orbiting Mars. GRB221009A had a structure of four bursts: less intense Pulse 1 - the triggering impulse - was detected by gamma-ray observatories at 131659 UT (near the Earth); the most intense Pulses 2 and 3 were detected on board all the spacecraft from the list, and Pulse 4 detected in more than 500 s after Pulse 1. Due to their different scientific objectives, the spacecraft, which data was used in this study, were separated by more than 1 AU (Solar Orbiter and MAVEN). This enabled tracking GRB221009A as it was propagating across the heliosphere. STEREO-A was the first to register Pulse 2 and 3 of the GRB, almost 100 seconds before their detection by spacecraft in the vicinity of Earth. MAVEN detected GRB221009A Pulses 2, 3, and 4 at the orbit of Mars about 237 seconds after their detection near Earth. By processing the time delays observed we show that the source location of the GRB221009A was at RA 288.5 degrees, Dec 18.5 degrees (J2000) with an error cone of 2 degrees

astro-ph.HE↗

arXiv2020

Harmonic radio emission in randomly inhomogeneous plasma

In present paper, we describe a theoretical model of generation of harmonic emissions of type III solar radio bursts. The goal of our study is to fully take into account the most efficient physical processes participating in generation of harmonic electromagnetic emission via nonlinear coupling of Langmuir waves in randomly inhomogeneous plasma of solar wind ($l+l^{'} \rightarrow t$). We revisit the conventional mechanism of coalescence of primarily generated and back-scattered Langmuir waves in quasihomogeneous plasma. Additionally, we propose and investigate another mechanism that generates the harmonic emission only in a strongly inhomogeneous plasma: the nonlinear coupling of incident and reflected Langmuir waves inside localized regions with enhanced plasma density (clumps), in the close vicinity of the reflection point. Both mechanisms imply the presence of strong density fluctuations in plasma. We use the results of a probabilistic model of beam-plasma interaction and evaluate the efficiency of energy transfer from Langmuir waves to harmonic emission. We infer that harmonic emissions from a quasihomogeneous plasma are significantly more intense than found in previous studies. The efficiency of Langmuir waves conversion into electromagnetic harmonic emission is expected to be higher at large heliospheric distances for the mechanism operating in quasihomogeneous plasma, and at small heliocentric distances - for the one operating in inhomogeneous. The evaluation of emission intensity in quasihomogeneous plasma may also be applied for type II solar radio bursts. The radiation pattern in both cases is quadrupolar, and we show that emission from density clumps may efficiently contribute to the visibility of harmonic radio emission.

physics.plasm-ph↗

arXiv2018

On the mechanism of radio emission in type III Solar Radiobursts

Type III solar radio bursts are generated by streams of energetic electrons accelerated at the Sun during periods of the solar activity. The generation occurs in two steps. Initially, electron beams generate electrostatic Langmuir waves and then these waves are transformed in electromagnetic emissions. It is widely accepted that the mechanism of generation of emission on fundamental frequency close to plasma frequency is due to induced scattering of Langmuir waves into electromagnetic. However this process imposes quite restrictive limit of the ratios of effective brightness temperatures of electromagnetic and Langmuir waves in the source region. Recent studies showed that the level of density fluctuations in the solar wind and in the solar corona is so high that it may significantly affect beam-plasma interaction. Here we show that the presence of intense density fluctuations not only crucially influence the process of beam plasma interaction but also changes the mechanism of energy transfer from electrostatic waves into electromagnetic. Reflection of the Langmuir waves from the density inhomogeneities may result in partial transformation of the energy of electrostatic wave into electromagnetic. We show that the linear wave energy transformation for the level of fluctuations of the order of 1\% or higher may be significantly more efficient for generation of type III solar radio bursts than conventionally considered process of nonlinear conversion due to induced scattering on ions.

astro-ph.SR↗