Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session MR13: Space Plasma Science |
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Chair: Gary Zank, University of Alabama-Huntsville Room: Virtual GEC platform |
Thursday, October 7, 2021 8:00AM - 8:15AM |
MR13.00001: Flux Ropes, Turbulence, and Collisionless Perpendicular Shock Waves: High Plasma Beta Case Gary P Zank, Masaru Nakanotani, Lingling Zhao, Senbei Du, Laxman Adhikari, Haihong Che, Jakobus A le Roux With the onset of solar maximum and the likely increased prevalence of interplanetary shock waves, Parker Solar Probe is likely to observe numerous shocks in the next few years. An outstanding question that has received surprisingly little attention has been how turbulence interacts with collisionless shock waves. Turbulence in the supersonic solar wind is described frequently as a superposition of a majority 2D and a minority slab component. We formulate a collisional perpendicular shock-turbulence transmission problem in a way that enables investigation of the interaction and transmission of quasi-perpendicular fluctuations such as magnetic flux ropes/islands and vortices as well as entropy and acoustic modes in the large plasma beta regime. We focus on the transmission of an upstream spectrum of these modes, finding that the downstream spectral amplitude is typically increased significantly (a factor of 10 or more), and that the upstream spectral index of the inertial range, and indeed the general spectral shape, is unchanged for the downstream magnetic variance, kinetic energy, and density variance. A comparison of the theoretically predicted downstream magnetic variance, kinetic energy, and destiny variance spectra with those observed at 1 au, 5 au, and 84 au by Wind, Ulysses, and Voyager 2 shows excellent agreement. The overall theoretically predicted characteristics of the transmission of turbulence across shocks observed in the solar wind appear to be largely consistent with recent observational studies by Pitna et al. 2016, Pitna et al. 2020, and Borovsky 2020. |
Thursday, October 7, 2021 8:15AM - 8:30AM |
MR13.00002: Coronal Loop Heating by Nearly Incompressible Magnetohydrodynamic Turbulence Mehmet S Yalim, Gary P Zank, Laxman Adhikari, Nikolai Pogorelov How is the solar corona heated? Physical models that address the question of heating of the solar corona fall into essentially two classes: Wave/turbulence-driven models and reconnection/loop-opening models. The transport of waves and turbulence beyond the photosphere is central to the coronal heating problem. In 2018, a new model that describes the transport and evolution of turbulence in the quiet solar corona was proposed and applied to a simple 1D model of the corona. This model utilizes the nearly incompressible magnetohydrodynamic (NI MHD) turbulence transport equations to describe the transport of low-frequency turbulence in open magnetic field regions. It describes the evolution of the coupled majority quasi-2D and minority slab component, driven by the magnetic carpet and advected by a subsonic, sub-Alfvenic flow from the lower corona. In this work, we couple the NI MHD turbulence transport model with an MHD model of solar corona to study the heating problem in a coronal loop. We find that a loop whose initial magnetic field topology consists of a uniform and strong axial guide field without any transverse small scale fields and braiding can be heated to ~1 million K by transport of Alfven wave turbulence described by the NI MHD turbulence transport model. |
Thursday, October 7, 2021 8:30AM - 8:45AM |
MR13.00003: Evolution of anisotropic turbulence in the fast and slow solar wind: Theory and Solar Orbiter measurements Laxman Adhikari, Gary P Zank, Lingling Zhao, Danielle Telloni, Tim Horbury, Helen O’Brien, Vincent Evans, Chris J Owen, Philippe Louarn, Andrei Fedorov Solar Orbiter (SolO) was launched on February 9, 2020, allowing us to study the nature of turbulence in the inner heliopshere. We investigate the evolution of anisotropic turbulence in the fast and slow solar wind in the inner heliosphere using the nearly incompressible magnetohydrodynamic (NI MHD) turbulence model and SolO measurements. We calculated the two dimensional (2D) and the slab variances of the energy in forward and backward propagating modes, the fluctuating magnetic energy, the fluctuating kinetic energy, the normalized residual energy, and the normalized cross-helicity as a function of the angle between the mean solar wind speed and the mean magnetic field θ_UB, and as a function of the heliocentric distance using SolO measurements. We compared the observed results and the theoretical results of the NI MHD turbulence model as a function of the heliocentric distance. The results show that the ratio of 2D energy and slab energy of forward and backward propagating modes, magnetic field fluctuations, and kinetic energy fluctuations increases as the angle between the mean solar wind flow and the mean magnetic field increases from θ_UB=0 deg to approximately θ_UB=90 deg and then decreases as θ_UB -> 180 deg. We find that solar wind turbulence is a superposition of the dominant 2D component and a minority slab component as a function of the heliocentric distance. We find excellent agreement between the theoretical results and observed results as a function of the heliocentric distance. |
Thursday, October 7, 2021 8:45AM - 9:00AM |
MR13.00004: Turbulence and wave transmission at an ICME-driven shock observed by the Solar Orbiter and Wind Lingling Zhao, Gary P Zank, Jiansen He, Daniele Telloni, Qiang Hu, Gang Li, Masaru Nakanotani, Laxman Adhikari, Emilia Kilpua, Tim Horbury Interplanetary shocks in the heliosphere have important consequences for the generation and evolution of solar wind turbulence. The direct effects of shock waves on nearby turbulence remains a controversial issue. An interplanetary coronal mass ejection (ICME) event was observed by the Solar Orbiter at 0.8 AU on 2020 April 19 and wind at 1 AU on 2020 April 20. Furthermore, an interplanetary shock wave was driven in front of the ICME. In this talk, we focus on the transmission of the magnetic fluctuations across the shock and analyze the characteristic wave modes of solar wind turbulence in the vicinity of the shock observed by both spacecraft. We find that the observed ICME-driven shock is a fast, forward oblique shock with a more perpendicular shock angle at the Wind position. After the shock crossing, the magnetic field fluctuation power increases. Most of the magnetic field fluctuation power resides in the transverse fluctuations. In the vicinity of the shock, both spacecraft observe right-hand polarized waves in the spacecraft frame. The upstream wave signatures fall within a relatively broad and low-frequency band, which might be attributed to low-frequency MHD waves excited by the streaming particles. For the downstream magnetic wave activity, we find oblique kinetic Alfvén waves with frequencies near the proton cyclotron frequency in the spacecraft frame. The frequency of the downstream waves increases by a factor of ∼7–10 due to the shock compression and the Doppler effect. |
Thursday, October 7, 2021 9:00AM - 9:15AM |
MR13.00005: Cosmic Ray-Dominated Shocks in the Hot Ionized Interstellar Medium Bingbing Wang, Gary P Zank, Lingling Zhao, Laxman Adhikari Galactic cosmic rays are energetic particles that are primarily accelerated by supernova remnant shocks. The back-reaction of energetic particles can modify the structure of the |
Thursday, October 7, 2021 9:15AM - 9:30AM |
MR13.00006: Density Turbulence and the Angular Broadening of Radio Sources in the high latitude and Ecliptic Planes Samira Tasnim, Gary P Zank, Iver H Cairns, Laxman Adhikari Density irregularities are responsible for the scattering of radio waves in the solar wind and astrophysical plasmas. These irregularities significantly affect the inferred physical properties of the radio sources, such as size, direction, and intensity. We present here a theory of angular broadening due to the scattering of radio waves by density irregularities that improves the existing formalism used to investigate radio wave scattering in the outer heliosphere (OH) and the very local interstellar medium (VLISM). The model includes an inner scale and both latitudinal and radial dependencies for the density fluctuation spectra and propagation paths for the radiation out of the ecliptic plane. Based on the pickup ion-mediated solar wind model (PUI model) of Zank {et al.} [2018], we estimate the turbulence and solar wind quantities for the high latitude fast solar wind. The predictions include the density variance, inner/dissipation scale, velocity correlation length, mean magnetic field, and proton temperature. The density turbulence amplitude is estimated in two ways. A simple scaling technique is used to extend the theoretical predictions of the PUI model for the high latitude wind beyond the heliospheric termination shock (HTS). The solar wind and turbulence quantities are calculated in the ecliptic plane using plasma and magnetometer data from the Voyager 2 spacecraft over the period 1977 to 2018. Based on the models and observations, we calculate the scattering angle of the radio sources in the high latitude and ecliptic wind. Finally, we compare the numerical results with the analytic predictions from Cairns [1995] and Armstrong {et al.} [2000]. |
Thursday, October 7, 2021 9:30AM - 9:45AM |
MR13.00007: Electron Acceleration and the Development of Power-Law Energy Spectra in Magnetic Reconnection with A Force-free Current Sheet Haihong Che, Arnold O Benz, Bofeng Tang, Chris Crawford Extensive observations have discovered that a huge number of energetic electrons with energy up to MeV (~0.9c and Lorentz factor ~2) are produced during solar flares. These very mild relativistic energetic electrons demonstrate two-stage power-law spectral evolutions. What mechanism efficiently accelerates non-relativistic particles to a power-law has been a long-standing “ injection problem” in particle acceleration theory since Fermi first proposed his famous Fermi-acceleration model in 1949. In this talk, I will discuss why particle acceleration in solar flares is an “injection problem” and what problems are with the previous and current widely invoked models. I will present a new acceleration mechanism in magnetic reconnection. I will show how the velocity shear stored naturally in force-free currents drives an electron Kevin-helmholtz instability (EKHI) during magnetic reconnection and efficiently acceleration electrons to a power-law energy spectrum via a two-stage soft-hard-hard evolution. Finally, I will discuss the potentially broad application of this mechanism in solar physics and how the complexity of solar flares may impact the further development of this model. |
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