Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session YO07: Space/Heliospheric PlasmasLive Streamed
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Chair: Arya Afshari, University of Iowa Room: 401 ABC |
Friday, October 21, 2022 9:30AM - 9:42AM |
YO07.00001: Suprathermal electrons in Earth's Magnetotail: a statistical picture Li-jen Chen, James F Drake, Ian J Cohen, Drew L Turner, Mitsuo Oka Based on measurements from NASA's Magnetospheric Multiscale mission, statistical analyses of suprathermal electrons in Earth's magnetotail reveal two main categories of magnetic configurations where suprathermal electrons are observed. The first one is created by the earthward flow of the reconnected magnetic flux. Occurrence of suprathermal electron flux enhancements peaks statistically at regions with elevated magnetic flux and weak plasma flows behind the reconnection front. The earthward transport of reconnected fluxes gives rise to an electric field in the same direction as the reconnection electric field. This electric field occurs in the region extending from the X line to the reconneciton front, much larger |
Friday, October 21, 2022 9:42AM - 9:54AM |
YO07.00002: Direct Observation of Ion Cyclotron Damping of Turbulence in Earth's Magnetosheath Plasma Arya S Afshari, Gregory G Howes, Jason Shuster, Daniel McGinnis, Mihailo M Martinovic, Kristopher G Klein, Craig A Kletzing, David P Hartley, Scott A Boardsen The turbulent cascade in heliospheric plasmas, such as the solar corona, solar wind, and Earth's magneotsheath, transfers energy to kinetic length scales at which poorly understood dissipation mechanisms damp the turbulent fluctuations and consequently energize the plasma particles. The dissipation mechanism in effect can be identified in the resulting velocity-space signature from applying the Field-Particle Correlation (FPC) technique. The FPC technique correlates the time series of the phase-space density measurements with that of the electric field fluctuations, both of which are measured by instrument suites aboard NASA's Magnetospheric Multiscale (MMS) mission. In a case study when the MMS spacecraft were located in the Earth's magnetosheath, we quantify the turbulent cascade rate in the inertial range and compare it to the dissipation of this energy at the ion kinetic scale through ion cyclotron damping, and at the electron kinetic scale through electron Landau damping. The distinct velocity-space signatures of these dissipation mechanisms allow us to differentiate between the two, as well as quantify the particle energization rate due to each. By comparing each species' energization rate with the turbulent cascade rate, we identify the dominant channel through which turbulent energy is dissipated. |
Friday, October 21, 2022 9:54AM - 10:06AM |
YO07.00003: Simulating Starfish: Numerical Investigation of the Starfish HANE EMP and Diamagnetic Cavity Evolution with Comparison to Observational Data Mikhail Belyaev Starfish Prime was a high altitude nuclear explosion (HANE) that produced a significant geomagnetic disturbance within the Earth's ionosphere. The E3 electromagnetic pulse (EMP) was recorded on Johnston Island, and sounding rockets measured the magnetic field evolution within the diamagnetic bubble (Dyal 2006). |
Friday, October 21, 2022 10:06AM - 10:18AM |
YO07.00004: Particle acceleration by nonlinear whistler precursors and possible reformation Lynn B Wilson An examination reveals the disruption, deceleration, and heating of the incident solar wind ion core population by nonlinear whistler precursor waves at a high Mach number, quasi-perpendicular shock observed by the four MMS spacecraft. The precursors propagate obliquely to the quasi-static magnetic field, the shock normal unit vector, and the incident bulk flow velocity vector, consistent with previous work. These large amplitude oscillations are not consistent with shock ripples -- Alfven-like oscillations on the surface of a shock that are linearly polarized and propagate along the shock surface. The oscillations examined here are elliptically-to-circularly polarized, not propagating along the shock surface, and have durations roughly seven times shorter than expected for shock ripples from theory. Their spatial scales range from a few 100 km down to several 10s of km, which corresponds to spatial scales spanning from from several upstream averaged ion inertial lengths to electron scales. The magnitude of the disruption and profile of the reduced ion distributions may suggest these nonlinear waves are causing the shock to reform; at the very least they induce local nonstationarity. |
Friday, October 21, 2022 10:18AM - 10:30AM |
YO07.00005: Nonlinear spectral analysis of ion acoustic solitary wave solutions to the forced Korteweg-de Vries equation Ian DesJardin, Christine M Hartzell Solitary ion acoustic waves (solitons) in a collisionless plasma can exhibit strong stability properties even though they are nonlinear. This makes them an attractive indirect sensing mechanism for sub-cm orbital debris in low Earth orbit which is unobservable. However, observations of these solitons from spacecraft or experiment rely on visual identification because solitons are broadband in a Fourier based analysis. In this work, we numerically implement a nonlinear spectral decomposition known as the Inverse Scattering Transform and demonstrate its ability to successfully detect solitons in simulations of the Korteweg-de Vries equation, which models ion acoustic dynamics. This spectral technique is applied to simulations of solitons generated by a 10 mm spherical debris object orbiting at an altitude of 2000km interacting with the ionospheric plasma. We demonstrate the feasibility of using this technique as a real time analysis tool for screening spacecraft data for solitons. |
Friday, October 21, 2022 10:30AM - 10:42AM |
YO07.00006: Generalized Theory of Weak Magnetohydrodynamic Turbulence Peter H Yoon The heliosphere is replete with Alfvenic fluctuations which are of solar origin. These are believed to be important in the context of the solar coronal heating and solar wind acceleration processes. The study of such low-frequency hydromagnetic turbulent phenomena is thus of compelling nature, especially in view of the contemporary space missions such as NASA's Parker Solar Probe and ESA's Solar Orbiter missions. Among the mathematical tools to study such turbulent phenomena is the weak turbulence theory. The weak magnetohydrodynamic (MHD) turbulence theory found in the literature often starts from the equations of incompressible MHD theory expressed via the Elsasser variables, and the derivation is carried out via a truncated solution at the second-order of iteration under the assumption of zero residual energy, which is the difference between the turbulent energy associated with the velocity fluctuation and the magnetic field fluctuation associated with the shear Alfven waves. The present paper generalizes the formulation of weak MHD turbulence theory by relaxing the assumption on the residual energy, and by retaining the iterative solution up to the third order. For this purpose, it is found that the pristine form of incompressible MHD equation, rather than that expressed in terms of Elsasser fields, offers a more straightforward theoretical platform. It is also found that the residual energy is generally finite, but in order to treat this proble properly, it is necessary to include the third-order nonlinear correction. |
Friday, October 21, 2022 10:42AM - 10:54AM |
YO07.00007: Preliminary Results for Experiment at WiPPL Khalil J Bryant, Rachel Young, Joseph R Olson, Cary B Forest, Carolyn C Kuranz The Sun, being an active star, undergoes eruptions of magnetic fields and charged particles that reach the Earth and cause the aurora near the poles. |
Friday, October 21, 2022 10:54AM - 11:06AM |
YO07.00008: Electric Fields and Electric Jets of the Sun and Solar Wind Charles F Driscoll A simple model of solar electric fields explains the solar wind energetics and coronal "heating", invoking only thermo-electric and photo-electric forces. In the (collisional) solar interior, thermal electron pressure generates a radial electric field eE ~ mpg/2. In the (less collisional) photospheric plasma "sheath", the outward photon energy flux Γε gives eE = σγe Γε /c. Here, the photon-electron cross-section σγe varies widely with density and temperature: The minimum (Thompson) cross-section is ~0.7 barn, but correlated 2- or 3-body “rydberg” states (and H-) have σγe ~ 10^8 barn. Here, a modelled σγe ~3x10^4 barn generates the observed solar wind: “collisional runaway” protons are accelerated out of the -2.keV gravity well and up to +1.3 keV within several Rs, accompanied by neutralizing electrons. Spatial variations will be caused by the solar surface convective cells, with runaway generation more prevalent in the cold downflow edges. Morever, plasma “pinch” dynamics may concentrate the edge acceleration into smaller “jets” (e.g. ~10.km), consistent with the “campfires” imaged by Solar Orbiter. This proton/electron flow will glow as the K-Corona, obviating the traditional T=200eV “hydrostatic un-charged electron gas” models. NNP.ucsd.edu/Solar. |
Friday, October 21, 2022 11:06AM - 11:18AM |
YO07.00009: Generation of Large-Scale Density Fluctuations near the Sun Xiangrong Fu, Zhaoming Gan, Hui Li As a signature of compressible solar wind, enhanced density fluctuations are reported by in-situ and remote sensing observations near the Sun. However, their generation mechanism remains elusive. In this study, we use MHD simulations to study the nature of fluid-scale density fluctuations and explore two possible generation mechanisms. The first one is parametric decay instability (PDI), where coherent density fluctuations are associated with the slow mode excited by a large amplitude Alfven wave in the low-beta environment. The PDI process is essentially 1D and it could explain some observed density fluctuations within ~15 solar radii, even those in the lower solar atmosphere. The second mechanism is nonlinear coupling to incompressible Alfvenic structures, which are found in 3D driven turbulence simulations. The structures are perpendicular to the background magnetic field. They have very low frequency and do not follow dispersion relation of any linear MHD wave. We examine the relation and interplay between these two mechanisms. |
Friday, October 21, 2022 11:18AM - 11:30AM |
YO07.00010: Fluid simulations of Farley-Buneman instabilities: Model description and applications Enrique L Rojas, David Hysell, Keaton J Burns It is generally accepted that modeling Farley-Buneman instabilities require resolving ion Landau damping to reproduce experimentally observed nonlinear features. Particle in cell (PIC) simulations have reproduced most of these at a computational cost that severely affects their scalability. This limitation hinders the study of non-local phenomena that require three dimensions or coupling with larger-scale processes. We argue that a variation of the five-moment fluid system can recreate several aspects of Farley-Buneman dynamics, such as density and phase speed saturation, wave turning, and heating. Furthermore, we show that this model offers an excellent qualitative agreement with a kinetic solver. Finally, we will outline some of the applications of this new approach for studying the coupling with larger-scale phenomena such as gradient drift instabilities, improving our interpretation of coherent backscatter from E-region irregularities, and refining conductivity estimates of Global Circulation Models. |
Friday, October 21, 2022 11:30AM - 11:42AM |
YO07.00011: Studying effects of Coulomb collisions on the temperatures of solar wind electrons using cylindrical VPIC simulations. Harsha Gurram, Jan Egedal, Stanislav A Boldyrev, Adam J Stanier Solar wind plasma expands from the hot solar corona, but its temperature does not decrease as fast as adiabatic expansion would predict. A first-principle kinetic derivation shows that the heating of the solar-wind electrons results from the energy exchange between strahl component and the electrons trapped between the electric potential and magnetic mirror walls (the core) [1]. In this work, we verified the kinetic model by studying the effects of weak Coulomb collisions on the temperature scaling of the isotropic part of the electrons using Cylindrical VPIC simulations. Cylindrical VPIC is a particle-in-cell code with $B_r \propto 1/r$ scaling and scattering rates that can be changed independently, making it perfect for simulating solar wind. In our analysis of electron distribution functions, we found the temperature of trapped electrons increases with the ratio $\nu_{ee}/\nu_{ei}$, higher the $\nu_{ee}/\nu_{ei}$ higher the electron temperatures, implying a strong correlation between the Coulomb collisions and electron temperatures as suggested by the collisional model. |
Friday, October 21, 2022 11:42AM - 11:54AM |
YO07.00012: Stochastic electron acceleration by temperature anisotropy instabilities in solar flares Mario A Riquelme, Alvaro Osorio, Daniel Verscharen, Lorenzo Sironi Using 2D particle-in-cell (PIC) plasma simulations we study electron acceleration by temperature anisotropy instabilities, in the case where the electron temperature perpendicular to the ambient magnetic field (B) is larger than the parallel temperature and assuming conditions typical of above-the-loop-top (ALT) sources in solar flares. We focus on the long-term effect of the instabilities by driving the anisotropy growth during the entire simulation time. This is done through externally forcing a growth of B in the simulation by imposing a shearing plasma velocity, as a way to resemble local turbulent motions. The growth of B makes the anisotropy grow due to electron magnetic moment conservation, and amplifies the ratio w_c,e/w_p,e (w_c,e and w_p,e are the electron cyclotron and plasma frequencies, respectively). When w_c,e/w_p,e ~ 1.5, electrons are efficiently accelerated by the inelastic scattering provided by parallel, electromagnetic z (PEMZ) modes. After B has grown by a factor ~4, the electron spectra show nonthermal, power-law tails that, depending on the initial w_c,e/w_p,e, have indices between ~2 and ~3.5 and can reach ~MeV energies. |
Friday, October 21, 2022 11:54AM - 12:06PM |
YO07.00013: Global structure of magnetotail reconnection inferred from data mining and implications for its MHD simulations Harry Arnold, Kareem Sorathia, Grant Stephens, Mikhail Sitnov, Viacheslav Merkin, Joachim Birn Recent advances in reconstructing the Earth's magnetic field and associated currents by utilizing data mining of in situ observations in the magnetosphere have proven remarkably accurate at reproducing observed ion diffusion regions. We investigate the effect of placing regions of localized resistivity in global simulations of the magnetosphere at specific locations inspired by the data mining results for the substorm occurring on July 6, 2017. Unsurprisingly, we are able to form x-lines at the same time and location as the MMS observation of an ion diffusion region at 15:35 UT on that day. Without this explicit resistivity, reconnection forms later in the substorm and far too close to the Earth ($\gtrsim-15R_E$), a common problem with global simulations of the Earth's magnetosphere. A consequence of reconnection taking place further in the tail due to localized resistivity is that the reconnection outflows transport magnetic flux Earthward and thus prevent the current sheet from thinning enough for reconnection to take place near the Earth. Interestingly, as these same flows rebound tailward from the inner magnetosphere, they can temporarily and locally (in the dawn-dusk direction) stretch the magnetic field allowing for small scale x-lines to form in the near Earth region. Due to the narrow extent of these x-lines ($\lesssim5R_E$) and their short lifespan ($\lesssim5$min), they will be difficult to observe by in situ measurements. Future work will explore time dependent resistivity to better match simulations with data mining reconstructions. |
Friday, October 21, 2022 12:06PM - 12:18PM |
YO07.00014: Thin Filament Oscillations: Pure Interchange in a Bubble Jason R Derr, Richard A Wolf, Frank Toffoletto Buoyancy waves are an important low-frequency wave mode in the Earth's magnetosphere that is akin to gravity waves in the Earth's atmosphere, but where gravity is replaced by magnetic tension. We have recently computed the eigenfrequencies and eigenfunctions of buoyancy waves using two different approaches: classic interchange theory and MHD ballooning. Interchange waves are not MHD waves, but rather assume a constant pressure $p$ along each field line. We found that in an average magnetosphere the ballooning and interchange modes are very similar for field lines that extend into the plasma sheet but differ somewhat in the inner magnetosphere [Toffoletto et al., 2022]. We found that the determining factor that controls whether a buoyancy wave is an interchange oscillation is the gradient of entropy $pV^\gamma$, where $V$ is the flux tube volume. Low entropy bubbles, which are ubiquitous in the magnetosphere, have a small entropy gradient, so one would expect very different buoyancy waves within the bubble compared to the background even in the inner magnetosphere. In the bubble scenario, we use a localized small negative entropy-gradient region which is unstable adjacent to a region where the entropy gradient is near-vanishing within which low frequency waves can occur. We find that inside the bubble the buoyancy frequencies are much lower and resemble pure interchange modes. |
Friday, October 21, 2022 12:18PM - 12:30PM Author not Attending |
YO07.00015: Electron heating associated with magnetic reconnection and magnetic holes in foreshock waves: PIC analysis Shan Wang, Naoki Bessho, Jonathan Ng Kinetic structures like magnetic reconnection and magnetic holes develop in the shock transition region. They are potentially important sites for contributing energy dissipation at the shock, but their roles in plasma heating are still unclear. One pathway of generating such kinetic structures is that the ion-ion instability in the foreshock region excites ion-scale waves, which grow into large amplitudes, compress, and form thin current layers or generate secondary instabilities that allow reconnection to occur. We perform a 2D particle-in-cell simulation starting from the ion-ion instability, which indeed develops reconnection and magnetic hole structures. The probability distribution of the electron temperature indicates that electron heating is enhanced around the reconnection X-line. Heating starts from the magnetic field compression process before forming thin current sheets, which may lead to complicated temperature profiles in individual current sheets, and the heating efficiency also has temporal variations. The simulation also shows development of magnetic hole structures, where magnetic fields compress to form magnetic bottle structures that gradually evolve into electron-scale magnetic holes associated with electron temperature enhancements. The correlation analysis between the magnetic field strength and electron temperature indicates that the electron heating is adiabatic at large scales with positive correlations, while non-adiabatic heating occurs at sub-ion scales where the correlation coefficients are negative. The results demonstrate the importance of sub-ion scale reconnection or magnetic holes in electron heating at shocks. |
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