1
|
Archer MO, Southwood DJ, Hartinger MD, Rastaetter L, Wright AN. How a Realistic Magnetosphere Alters the Polarizations of Surface, Fast Magnetosonic, and Alfvén Waves. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2022; 127:e2021JA030032. [PMID: 35864843 PMCID: PMC9286832 DOI: 10.1029/2021ja030032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 12/10/2021] [Accepted: 01/12/2022] [Indexed: 06/15/2023]
Abstract
System-scale magnetohydrodynamic (MHD) waves within Earth's magnetosphere are often understood theoretically using box models. While these have been highly instructive in understanding many fundamental features of the various wave modes present, they neglect the complexities of geospace such as the inhomogeneities and curvilinear geometries present. Here, we show global MHD simulations of resonant waves impulsively excited by a solar wind pressure pulse. Although many aspects of the surface, fast magnetosonic (cavity/waveguide), and Alfvén modes present agree with the box and axially symmetric dipole models, we find some predictions for large-scale waves are significantly altered in a realistic magnetosphere. The radial ordering of fast mode turning points and Alfvén resonant locations may be reversed even with monotonic wave speeds. Additional nodes along field lines that are not present in the displacement/velocity occur in both the perpendicular and compressional components of the magnetic field. Close to the magnetopause, the perpendicular oscillations of the magnetic field have the opposite handedness to the velocity. Finally, widely used detection techniques for standing waves, both across and along the field, can fail to identify their presence. We explain how all these features arise from the MHD equations when accounting for a non-uniform background field and propose modified methods that might be applied to spacecraft observations.
Collapse
Affiliation(s)
- M. O. Archer
- Space and Atmospheric Physics Group, Department of PhysicsImperial College LondonLondonUK
| | - D. J. Southwood
- Space and Atmospheric Physics Group, Department of PhysicsImperial College LondonLondonUK
| | | | | | - A. N. Wright
- Department of Mathematics and StatisticsUniversity of St AndrewsSt AndrewsUK
| |
Collapse
|
2
|
Viall NM, Borovsky JE. Nine Outstanding Questions of Solar Wind Physics. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2020; 125:e2018JA026005. [PMID: 32728511 PMCID: PMC7380306 DOI: 10.1029/2018ja026005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 01/15/2020] [Accepted: 01/22/2020] [Indexed: 06/11/2023]
Abstract
In situ measurements of the solar wind have been available for almost 60 years, and in that time plasma physics simulation capabilities have commenced and ground-based solar observations have expanded into space-based solar observations. These observations and simulations have yielded an increasingly improved knowledge of fundamental physics and have delivered a remarkable understanding of the solar wind and its complexity. Yet there are longstanding major unsolved questions. Synthesizing inputs from the solar wind research community, nine outstanding questions of solar wind physics are developed and discussed in this commentary. These involve questions about the formation of the solar wind, about the inherent properties of the solar wind (and what the properties say about its formation), and about the evolution of the solar wind. The questions focus on (1) origin locations on the Sun, (2) plasma release, (3) acceleration, (4) heavy-ion abundances and charge states, (5) magnetic structure, (6) Alfven waves, (7) turbulence, (8) distribution-function evolution, and (9) energetic-particle transport. On these nine questions we offer suggestions for future progress, forward looking on what is likely to be accomplished in near future with data from Parker Solar Probe, from Solar Orbiter, from the Daniel K. Inouye Solar Telescope (DKIST), and from Polarimeter to Unify the Corona and Heliosphere (PUNCH). Calls are made for improved measurements, for higher-resolution simulations, and for advances in plasma physics theory.
Collapse
|
3
|
He F, Guo RL, Dunn WR, Yao ZH, Zhang HS, Hao YX, Shi QQ, Rong ZJ, Liu J, Tian AM, Zhang XX, Wei Y, Zhang YL, Zong QG, Pu ZY, Wan WX. Plasmapause surface wave oscillates the magnetosphere and diffuse aurora. Nat Commun 2020; 11:1668. [PMID: 32245960 PMCID: PMC7125146 DOI: 10.1038/s41467-020-15506-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 03/16/2020] [Indexed: 11/09/2022] Open
Abstract
Energy circulation in geospace lies at the heart of space weather research. In the inner magnetosphere, the steep plasmapause boundary separates the cold dense plasmasphere, which corotates with the planet, from the hot ring current/plasma sheet outside. Theoretical studies suggested that plasmapause surface waves related to the sharp inhomogeneity exist and act as a source of geomagnetic pulsations, but direct evidence of the waves and their role in magnetospheric dynamics have not yet been detected. Here, we show direct observations of a plasmapause surface wave and its impacts during a geomagnetic storm using multi-satellite and ground-based measurements. The wave oscillates the plasmapause in the afternoon-dusk sector, triggers sawtooth auroral displays, and drives outward-propagating ultra-low frequency waves. We also show that the surface-wave-driven sawtooth auroras occurred in more than 90% of geomagnetic storms during 2014-2018, indicating that they are a systematic and crucial process in driving space energy dissipation.
Collapse
Affiliation(s)
- Fei He
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| | - Rui-Long Guo
- Laboratoire de Physique Atmosphérique et Planétaire, STAR Institute, Université de Liège, Liège, B-4000, Belgium
| | - William R Dunn
- Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
| | - Zhong-Hua Yao
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| | - Hua-Sen Zhang
- Institute of Applied Physics and Computational Mathematics, Beijing, 100088, China
| | - Yi-Xin Hao
- Institute of Space Physics and Applied Technology, Peking University, Beijing, 100871, China
| | - Quan-Qi Shi
- School of Space Science and Physics, Shandong University, Weihai, 264209, China
| | - Zhao-Jin Rong
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| | - Jiang Liu
- Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, 90095, USA
| | - An-Min Tian
- School of Space Science and Physics, Shandong University, Weihai, 264209, China
| | - Xiao-Xin Zhang
- Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, Beijing, 100081, China.
| | - Yong Wei
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China.
| | - Yong-Liang Zhang
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - Qiu-Gang Zong
- Institute of Space Physics and Applied Technology, Peking University, Beijing, 100871, China
| | - Zu-Yin Pu
- Institute of Space Physics and Applied Technology, Peking University, Beijing, 100871, China
| | - Wei-Xing Wan
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| |
Collapse
|
4
|
Wing S, Johnson JR. Applications of Information Theory in Solar and Space Physics. ENTROPY 2019; 21:e21020140. [PMID: 33266856 PMCID: PMC7514618 DOI: 10.3390/e21020140] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 01/18/2019] [Accepted: 01/20/2019] [Indexed: 11/16/2022]
Abstract
Characterizing and modeling processes at the sun and space plasma in our solar system are difficult because the underlying physics is often complex, nonlinear, and not well understood. The drivers of a system are often nonlinearly correlated with one another, which makes it a challenge to understand the relative effects caused by each driver. However, entropy-based information theory can be a valuable tool that can be used to determine the information flow among various parameters, causalities, untangle the drivers, and provide observational constraints that can help guide the development of the theories and physics-based models. We review two examples of the applications of the information theoretic tools at the Sun and near-Earth space environment. In the first example, the solar wind drivers of radiation belt electrons are investigated using mutual information (MI), conditional mutual information (CMI), and transfer entropy (TE). As previously reported, radiation belt electron flux (Je) is anticorrelated with solar wind density (nsw) with a lag of 1 day. However, this lag time and anticorrelation can be attributed mainly to the Je(t + 2 days) correlation with solar wind velocity (Vsw)(t) and nsw(t + 1 day) anticorrelation with Vsw(t). Analyses of solar wind driving of the magnetosphere need to consider the large lag times, up to 3 days, in the (Vsw, nsw) anticorrelation. Using CMI to remove the effects of Vsw, the response of Je to nsw is 30% smaller and has a lag time <24 h, suggesting that the loss mechanism due to nsw or solar wind dynamic pressure has to start operating in <24 h. Nonstationarity in the system dynamics is investigated using windowed TE. The triangle distribution in Je(t + 2 days) vs. Vsw(t) can be better understood with TE. In the second example, the previously identified causal parameters of the solar cycle in the Babcock-Leighton type model such as the solar polar field, meridional flow, polar faculae (proxy for polar field), and flux emergence are investigated using TE. The transfer of information from the polar field to the sunspot number (SSN) peaks at lag times of 3-4 years. Both the flux emergence and the meridional flow contribute to the polar field, but at different time scales. The polar fields from at least the last 3 cycles contain information about SSN.
Collapse
Affiliation(s)
- Simon Wing
- Applied Physics Laboratory, the Johns Hopkins University, Laurel, MD 20723-6099, USA
- Correspondence: ; Tel.: +1-240-228-8075
| | | |
Collapse
|
5
|
Claudepierre SG, Toffoletto FR, Wiltberger M. Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2016; 121:227-244. [PMID: 27668142 PMCID: PMC5020600 DOI: 10.1002/2015ja022048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2015] [Revised: 11/20/2015] [Accepted: 12/07/2015] [Indexed: 06/06/2023]
Abstract
We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.
Collapse
Affiliation(s)
| | | | - M. Wiltberger
- High Altitude ObservatoryNational Center for Atmospheric ResearchBoulderColoradoUSA
| |
Collapse
|
6
|
Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss. Nature 2015; 523:193-5. [PMID: 26123022 DOI: 10.1038/nature14515] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Accepted: 05/05/2015] [Indexed: 11/09/2022]
Abstract
Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high plasma density called the plasmasphere, within four to five Earth radii, arises largely from interaction with an electromagnetic plasma wave called plasmaspheric hiss. This interaction strongly influences the evolution of the radiation belts during a geomagnetic storm, and over the course of many hours to days helps to return the radiation-belt structure to its 'quiet' pre-storm configuration. Observations have shown that the long-term electron-loss rate is consistent with this theory but the temporal and spatial dynamics of the loss process remain to be directly verified. Here we report simultaneous measurements of structured radiation-belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated by hiss-scattered electrons colliding with the Earth's atmosphere after removal from the radiation belts. Our results show that changes of up to an order of magnitude in the dynamics of electron loss arising from hiss occur on timescales as short as one to twenty minutes, in association with modulations in plasma density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. This nearly global-scale coherence was not predicted and may affect the short-term evolution of the radiation belts during active times.
Collapse
|
7
|
Kavosi S, Raeder J. Ubiquity of Kelvin-Helmholtz waves at Earth's magnetopause. Nat Commun 2015; 6:7019. [PMID: 25960122 PMCID: PMC4432594 DOI: 10.1038/ncomms8019] [Citation(s) in RCA: 116] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 03/24/2015] [Indexed: 11/09/2022] Open
Abstract
Magnetic reconnection is believed to be the dominant process by which solar wind plasma enters the magnetosphere. However, for periods of northward interplanetary magnetic field (IMF) reconnection is less likely at the dayside magnetopause, and Kelvin-Helmholtz waves (KHWs) may be important agents for plasma entry and for the excitation of ultra-low-frequency (ULF) waves. The relative importance of KHWs is controversial because no statistical data on their occurrence frequency exist. Here we survey 7 years of in situ data from the NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) mission and find that KHWs occur at the magnetopause ∼19% of the time. The rate increases with solar wind speed, Alfven Mach number and number density, but is mostly independent of IMF magnitude. KHWs may thus be more important for plasma transport across the magnetopause than previously thought, and frequently drive magnetospheric ULF waves.
Collapse
Affiliation(s)
- Shiva Kavosi
- Department of Physics and Space Science Center, University of New Hampshire, 8 College Road, Durham, New Hampshire 03824, USA
| | - Joachim Raeder
- Department of Physics and Space Science Center, University of New Hampshire, 8 College Road, Durham, New Hampshire 03824, USA
| |
Collapse
|
8
|
Ukhorskiy AY, Sitnov MI, Millan RM, Kress BT, Fennell JF, Claudepierre SG, Barnes RJ. Global storm time depletion of the outer electron belt. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2015; 120:2543-2556. [PMID: 27656334 PMCID: PMC5014085 DOI: 10.1002/2014ja020645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Revised: 03/04/2015] [Accepted: 03/04/2015] [Indexed: 06/06/2023]
Abstract
The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by orders of magnitude at different spatial and temporal scales. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of 17 March 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 h after the sudden storm commencement. For the analysis we used three-dimensional test particle simulations of global evolution of the outer belt in the Tsyganenko-Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the Magnetic Electron Ion Spectrometer experiment shows that magnetopause loss accounts for most of the observed depletion at L>5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion.
Collapse
Affiliation(s)
- A. Y. Ukhorskiy
- Johns Hopkins University Applied Physics LaboratoryLaurelMarylandUSA
| | - M. I. Sitnov
- Johns Hopkins University Applied Physics LaboratoryLaurelMarylandUSA
| | - R. M. Millan
- Department of Physics and AstronomyDartmouth CollegeHanoverNew HampshireUSA
| | - B. T. Kress
- Cooperative Institute for Research in Environmental SciencesUniversity of Colorado at BoulderBoulderColoradoUSA
| | | | | | - R. J. Barnes
- Johns Hopkins University Applied Physics LaboratoryLaurelMarylandUSA
| |
Collapse
|