Kinetic Electrostatic Waves and their Association with Current Structures in the Solar Wind
D. B. Graham, Yu. V. Khotyaintsev, A. Vaivads, N. J. T. Edberg, A. I. Eriksson, E. Johansson, L. Sorriso-Valvo, M. Maksimovic, J. Souček, D. Píša, S. D. Bale, T… 展开作者
D. B. Graham, Yu. V. Khotyaintsev, A. Vaivads, N. J. T. Edberg, A. I. Eriksson, E. Johansson, L. Sorriso-Valvo, M. Maksimovic, J. Souček, D. Píša, S. D. Bale, T. Chust, M. Kretzschmar, V. Krasnoselskikh, E. Lorfèvre, D. Plettemeier, M. Steller, Š. Štverák, P. Trávníček, A. Vecchio, T. S. Horbury, H. O'Brien, V. Evans, V. Angelini
A variety of kinetic waves develop in the solar wind. The relationship between these waves and larger-scale structures, such as current sheets and ongoing turbulence remain a topic of investigation. Similarly, the instabilities producing ion-acoustic waves in the solar wind remains an open question. The goals of this paper are to investigate kinetic electrostatic Langmuir and ion-acoustic waves in the solar wind at 0.5 AU and determine whether current sheets and associated streaming instabilities can produce the observed waves. The relationship between these waves and currents is investigated statistically. Solar Orbiter's Radio and Plasma Waves instrument suite provides high-resolution snapshots of the fluctuating electric field. The Low Frequency Receiver resolves the waveforms of ion-acoustic waves and the Time Domain Sampler resolves the waveforms of both ion-acoustic and Langmuir waves. Using these waveform data we determine when these waves are observed in relation to current structures in the solar wind, estimated from the background magnetic field. Langmuir and ion-acoustic waves are frequently observed in the solar wind. Ion-acoustic waves are observed about 1% of the time at 0.5 AU. The waves are more likely to be observed in regions of enhanced currents. However, the waves typically do not occur at current structures themselves. The observed currents in the solar wind are too small to drive instability by the relative drift between single ion and electron populations. When multi-component ion and/or electron distributions are present the observed currents may be sufficient for instability. Ion beams are the most plausible source of ion-acoustic waves. The spacecraft potential is confirmed to be a reliable probe of the background electron density by comparing the peak frequencies of Langmuir waves with the plasma frequency calculated from the spacecraft potential.
Recent observation of large amplitude Langmuir waveforms during a Type III event in the solar wind have been interpreted as the signature of the electrostatic decay of beam-driven Langmuir waves. This mechanism is thought to be a first step to explain the generation of solar Type III radio emission. The threshold for this parametric instability in typical solar wind condition is investigated here by means of 1D-1V Vlasov-Poisson simulations. We show that the amplitude of the observed Langmuir beat-like waveforms is of the order of the effective threshold computed from the full kinetic simulati…
For more than 12 hours beginning on January 18, 2021, continuous narrowband electrostatic emissions were observed on Parker Solar Probe near 20 solar radii. The observed <1000 Hz frequencies were well below the local ion plasma frequency. Surprisingly, the emissions consisted of electrostatic wave packets with shock-like envelopes, appearing repetitively at a ~1.5 Hz rate. This repetitiveness correlated and was in phase with low frequency electromagnetic fluctuations. The emissions were associated with simultaneously observed ion beams and conditions favorable for ion-acoustic wave excitation,…
Several studies in the near-Earth environment show that intermittent structures are important sites of energy dissipation and particle energization. Recent Parker Solar Probe (PSP) data, sampled in the near-Sun environment, have shown that proton heating is concentrated near coherent structures, suggesting local heating of protons by turbulent cascade in this region. However, whether electrons exhibit similar behavior in the near-Sun environment is not clear. Here, we address this question using PSP data collected near the Sun during the first seven orbits. We use the partial variance of incre…
Above lunar crustal magnetic anomalies, large fractions of solar wind electrons and ions can be scattered and stream back towards the solar wind flow, leading to a number of interesting effects such as electrostatic instabilities and waves. These electrostatic structures can also interact with the background plasma, resulting in electron heating and scattering. We study the electrostatic waves and electron heating observed over the lunar magnetic anomalies by analyzing data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecr…
The observation of parallel ion velocity in the near-lunar wake approximately equal to external solar wind velocity \emph{can} be explained within uncertainties by an analytic electrostatic expansion model. The one-dimensional model frequently used is inadequate because it does not account for the moon's spherical shape. However, application of a more recent generalization to three-dimensions of the solution along characteristics predicts higher velocities, and is probably sufficient to account for the SARA observations on the Chandrayaan-1 space-craft.
A new electrostatic ramjet space engine is proposed and analyzed. The upper atmosphere (85 -1000 km) is extremely dense in ions (millions per cubic cm). The interplanetary medium contains positive protons from the solar wind. A charged ball collects the ions (protons) from the surrounding area and a special electric engine accelerates the ions to achieve thrust or decelerates the ions to achieve drag. The thrust may have a magnitude of several Newtons. If the ions are decelerated, the engine produces a drag and generates electrical energy. The theory of the new engine is developed. It is shown…
Electrostatic structures have been observed in many regions of space plasmas, including the solar wind, the magnetosphere, the auroral acceleration region, and in association with shocks, turbulence, and magnetic reconnection. Due to potentially large amplitude of electric fields within these structures, their effects on particle heating, scattering, or acceleration can be important. One possible theoretical description of some of these structures is the concept of Bernstein-Greene-Kruskal (BGK) modes, which are exact nonlinear solutions of the Vlasov-Poisson system of equations in collisionle…
Large amplitude whistler waves at frequencies of 0.2 to 0.4 times electron cyclotron frequency are frequently observed in the solar wind. The waves are obliquely propagating close to the resonance cone, with significant electric fields parallel to the background magnetic field, enabling strong interactions with electrons. Propagation angles are distinctly different from whistlers usually observed in the solar wind, and amplitudes are significantly larger. Waves occur most often in association with stream interaction regions (SIRs), and are often close-packed. 68 percent of the 54 SIRs had narr…
The solar wind escapes from the solar corona and is accelerated, over a short distance, to its terminal velocity. The energy balance associated with this acceleration remains poorly understood. To quantify the global electrostatic contribution to the solar wind dynamics, we empirically estimate the ambipolar electric field ($\mathrm{E}_\parallel$) and potential ($Φ_\mathrm{r,\infty}$). We analyse electron velocity distribution functions (VDFs) measured in the near-Sun solar wind, between 20.3\,$R_S$ and 85.3\,$R_S$, by the Parker Solar Probe. We test the predictions of two different solar wind…
Electric field measurements of the Time Domain Sampler (TDS) receiver, part of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter, often exhibit very intense broadband wave emissions at frequencies below 20~kHz in the spacecraft frame. In this paper, we present a year-long study of electrostatic fluctuations observed in the solar wind at an interval of heliocentric distances from 0.5 to 1~AU. The RPW/TDS observations provide a nearly continuous data set for a statistical study of intense waves below the local plasma frequency. The on-board and continuously collected and process…
We present a statistical study of the characteristics of very large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data from the Wind spacecraft as an addition of the study by Kellogg et al., [2010b]. We observed 244(65) whistler waves using electric(magnetic) field data from the Wind spacecraft finding ~40%(~62%) of the waves have peak-to-peak amplitudes of >/- 50 mV/m(>/- 0.5 nT). We present an example waveform capture of the largest magnetic field amplitude (>/- 8 nT peak-to-peak) whistler wave ever reported in the radiation belts. The estimated Poyntin…
The solar wind wake behind the moon is studied with 1D electrostatic particle-in-cell (PIC) simulations using a physical ion to electron mass ratio (unlike prior investigations); the simulations also apply more generally to supersonic flow of dense magnetized plasma past non-magnetic objects. A hybrid electrostatic Boltzmann electron treatment is first used to investigate the ion stability in the absence of kinetic electron effects, showing that the ions are two-stream unstable for downstream wake distances (in lunar radii) greater than about three times the solar wind Mach number. Simulations…
We use data from the first six encounters of Parker Solar Probe and employ the Partial Variance of Increments ($PVI$) method to study the statistical properties of coherent structures in the inner heliosphere with the aim of exploring physical connections between magnetic field intermittency and observable consequences such as plasma heating and turbulence dissipation. Our results support proton heating localized in the vicinity of, and strongly correlated with, magnetic structures characterized by $PVI \geq 1$. We show that on average, such events constitute $\approx 19\%$ of the dataset, tho…
The anticorrelated distributions of temperature and density of protons are a well-known property of the solar wind. Nevertheless, it is unclear till now if they are formed by some kind of the universal physical mechanism? Unfortunately, a straightforward comparison of the characteristic relaxation times for the temperature and density, on the one hand, and pressure, on the other hand, encounters the problem of inapplicability of the hydrodynamical approach in the situation when the free-path length of the protons is considerably greater than the spatial scale of the structures under considerat…
Electrostatic analyzers of different designs have been used since the earliest days of the space age, beginning with the very earliest solar wind measurements made by Mariner 2 en route to Venus in 1962. The Parker Solar Probe (PSP) mission, NASA's first dedicated mission to study the innermost reaches of the heliosphere, makes its thermal plasma measurements using a suite of instruments called the Solar Wind Electrons, Alphas, and Protons (SWEAP) investigation. SWEAP's electron Parker Solar Probe Analyzer (SPAN-E) instruments are a pair of top-hat electrostatic analyzers on PSP that are capab…
It has long been known that the high-speed stream (HSS) peak velocity at Earth directly depends on the area of the coronal hole (CH) on the Sun. Different degrees of association between the two parameters have been shown by many authors. In this study, we revisit this association in greater detail for a sample of 45 nonpolar CHs during the minimum phase of solar cycle 24. The aim is to understand how CHs of different properties influence the HSS peak speeds observed at Earth and draw from this to improve solar wind modeling. The characteristics of the CHs of our sample were extracted based on …
The dynamical relationship between magnetic storms and magnetospheric substorms presents one of the most controversial problems of contemporary geospace research. Here, we tackle this issue by applying a causal inference approach to two corresponding indices in conjunction with several relevant solar wind variables. We demonstrate that the vertical component of the interplanetary magnetic field is the strongest and common driver of both, storms and substorms, and explains their the previously reported association. These results hold during both solar maximum and minimum phases and suggest that…
We present the first observations of large amplitude waves in a well-defined electron diffusion region at the sub-solar magnetopause using data from one THEMIS satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves and electrostatic electron cyclotron waves, are observed in the same 12-sec waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistle…
Isolated electrostatic structures are observed throughout much of the 4 Re by 19.6 Re Cluster orbit. These structures are observed in the Wideband plasma wave instrument's waveform data as bipolar and tripolar pulses. These structures are observed at all of the boundary layers, in the solar wind and magnetosheath, and along auroral field lines at 4.5-6.5 Re. Using the Wideband waveform data from the various Cluster spacecraft we have carried out a survey of the amplitudes and time durations of these structures and how these quantities vary with the local magnetic field strength. Such a survey …
