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Results for “Magnetospheric physics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The impact of cold electrons and cold ions in magnetospheric physics

A review of the impact of the cold-ion and cold-electron populations in the Earth’s magnetosphere is presented in this paper. The cold populations are defined by total energy less than approximately 100 eV, i.e. in the energy range which is strongly affected by spacecraft charging and that often dominates the total plasma density. We also include the warm plasma cloak in the review, since it overlaps partially with the cold energy range and is a population that is still not well understood. The known impacts of cold ions and cold electrons that are discussed are: the source of magnetospheric plasma, solar-wind/magnetosphere coupling, magnetotail reconnection and substorms, Kelvin-Helmholtz instabilities at the magnetopause, chorus, hiss, electromagnetic-ion-cyclotron and ultra-low-frequency wave-particle interactions, aurora structuring and spacecraft charging. Other possible impacts are associated with refilling on open-drift trajectories, the remnant layer and plasmapause disruption. A discussion of the difficulty of cold-plasma measurements and the need for new measurement techniques that measure the full cold-ion and cold-electron distribution functions is also presented. There remain a lot of unknowns about the cold-ion and cold-electron populations, associated with their origin, properties, drivers and impacts. These populations will need to be fully understood before the magnetosphere-ionosphere system can be fully understood.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Outstanding questions in magnetospheric plasma physics: The pollenzo view

Based on discussions held at a workshop in Bra-Pollenzo, Italy, this paper elaborates upon 19 outstanding questions of plasma physics in the Earth's magnetosphere. The questions are grouped according to (a) driving processes, (b) radiation belt and ring current issues, (c) auroral physics, (d) internal plasma processes, and (e) magnetosphere-ionosphere mapping issues. Future needs for magnetospheric plasma physics (measurements, techniques, simulations, theories, studies) are outlined.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Determining the rotation direction in pulsars

Abstract Pulsars are rotating neutron stars emitting lighthouse-like beams. Owing to their unique properties, pulsars are a unique astrophysical tool to test general relativity, inform on matter in extreme conditions, and probe galactic magnetic fields. Understanding pulsar physics and emission mechanisms is critical to these applications. Here we show that mechanical-optical rotation in the pulsar magnetosphere affects polarisation in a way which is indiscernible from Faraday rotation in the interstellar medium for typical GHz observations frequency, but which can be distinguished in the sub-GHz band. Besides being essential to correct for possible systematic errors in interstellar magnetic field estimates, this result offers a unique means to determine the rotation direction of pulsars, providing additional constraints on magnetospheric physics. With the ongoing development of sub-GHz observation capabilities, our finding promises discoveries, such as the spatial distribution of pulsars rotation directions, which could exhibit potentially interesting, but presently invisible, correlations or features.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Evolution of a Relativistic Electron Beam for Tracing Magnetospheric Field Lines

Tracing magnetic field-lines of the Earth's magnetosphere using beams of relativistic electrons will open up new insights into space weather and magnetospheric physics. Analytic models and a single-particle-motion code were used to explore the dynamics of an electron beam emitted from an orbiting satellite and propagating until impact with the Earth. The impact location of the beam on the upper atmosphere is strongly influenced by magnetospheric conditions, shifting up to several degrees in latitude between different phases of a simulated storm. The beam density cross-section evolves due to cyclotron motion of the beam centroid and oscillations of the beam envelope. The impact density profile is ring shaped, with major radius ~22 m, given by the final cyclotron radius of the beam centroid, and ring thickness ~2 m given by the final beam envelope. Motion of the satellite may also act to spread the beam, however it will remain sufficiently focused for detection by ground-based optical and radio detectors. Furthermore, an array of such ground stations will be able to detect shifts in impact location of the beam, and thereby infer information regarding magnetospheric conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The Global Positioning System constellation as a space weather monitor. Comparison of electron measurements with Van Allen Probes data

Energetic electron observations in Earth's radiation belts are typically sparse, and multipoint studies often rely on serendipitous conjunctions. This paper establishes the scientific utility of the Combined X-ray Dosimeter (CXD), currently flown on 19 satellites in the Global Positioning System (GPS) constellation, by cross-calibrating energetic electron measurements against data from the Van Allen Probes. By breaking our cross calibration into two parts—one that removes any spectral assumptions from the CXD flux calculation and one that compares the energy spectra—we first validate the modeled instrument response functions, then the calculated electron fluxes. Unlike previous forward modeling of energetic electron spectra, we use a combination of four distributions that together capture a wide range of observed spectral shapes. Moreover, our two-step approach allowed us to identify, and correct for, small systematic offsets between block IIR and IIF satellites. Using the Magnetic Electron Ion Spectrometer and Relativistic Electron-Proton Telescope on Van Allen Probes as a “gold standard,” here we demonstrate that the CXD instruments are well understood. A robust statistical analysis shows that CXD and Van Allen Probes fluxes are similar and the measured fluxes from CXD are typically within a factor of 2 of Van Allen Probes at energies inline image4 MeV. Our team present data from 17 CXD-equipped GPS satellites covering the 2015 “St. Patrick's Day” geomagnetic storm to illustrate the scientific applications of such a high data density satellite constellation and therefore demonstrate that the GPS constellation is positioned to enable new insights in inner magnetospheric physics and space weather forecasting.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Self-consistent modeling of electron precipitation and responses in the ionosphere: application to low-altitude energization during substorms

Here, we report a new modeling capability that self–consistently couples physics–based magnetospheric electron precipitation with its impact on the ionosphere. Specifically, the ring current model RAM–SCBE is two–way coupled to an ionospheric electron transport model GLOW, representing a significant improvement over previous models, in which the ionosphere is either treated as a 2D spherical boundary of the magnetosphere, or is driven by empirical precipitation models that are incapable of capturing small–scale, transient variations. The new model enables us to study the impact of substorm–associated, spectrum–resolved electron precipitation on the 3D ionosphere. We found that after each substorm injection, a high–energy tail of precipitation is produced in the dawn sector outside the plasmapause, by energetic electrons (10 < E < 100 keV) scattered by whistler–mode chorus waves. Consequently, an ionospheric sub–layer characterized by enhanced Pedersen conductivity arises at unusually low altitude (~85 km), with its latitudinal width of ~5–10° in the auroral zone. The sub–layer structure appears intermittently, in correlation with recurrent substorm injections. It propagates eastward from the nightside to the dayside in the same drift direction of source electrons injected from the plasmasheet, resulting in global impact within the ionosphere. In conclusion, this study demonstrates the model's capability of revealing complex cross–scale interactions in the geospace environment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Fast Diffusion of Ultrarelativistic Electrons in the Outer Radiation Belt: 17 March 2015 Storm Event

Inward radial diffusion driven by ULF waves has long been known to be capable of accelerating radiation belt electrons to very high energies within the heart of the belts, but more recent work has shown that radial diffusion values can be highly event-specific, and mean values or empirical models may not capture the full significance of radial diffusion to acceleration events. Here we present an event of fast inward radial diffusion, occurring during a period following the geomagnetic storm of 17 March 2015. Ultrarelativistic electrons up to ~8 MeV are accelerated in the absence of intense higher-frequency plasma waves, indicating an acceleration event in the core of the outer belt driven primarily or entirely by ULF wave-driven diffusion. We examine this fast diffusion rate along with derived radial diffusion coefficients using particle and fields instruments on the Van Allen Probes spacecraft mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Prediction of the SYM-H Index Using a Bayesian Deep Learning Method With Uncertainty Quantification

We propose a novel deep learning framework, named SYMHnet, which employs a graph neural network and a bidirectional long short-term memory network to cooperatively learn patterns from solar wind and interplanetary magnetic field parameters for short-term forecasts of the SYM-H index based on 1- and 5-min resolution data. SYMHnet takes, as input, the time series of the parameters' values provided by NASA's Space Science Data Coordinated Archive and predicts, as output, the SYM-H index value at time point t + w hours for a given time point t where w is 1 or 2. By incorporating Bayesian inference into the learning framework, SYMHnet can quantify both aleatoric (data) uncertainty and epistemic (model) uncertainty when predicting future SYM-H indices. Experimental results show that SYMHnet works well at quiet time and storm time, for both 1- and 5-min resolution data. The results also show that SYMHnet generally performs better than related machine learning methods. For example, SYMHnet achieves a forecast skill score (FSS) of 0.343 compared to the FSS of 0.074 of a recent gradient boosting machine (GBM) method when predicting SYM-H indices (1 hr in advance) in a large storm (SYM-H = -393 nT) using 5-min resolution data. When predicting the SYM-H indices (2 hr in advance) in the large storm, SYMHnet achieves an FSS of 0.553 compared to the FSS of 0.087 of the GBM method. In addition, SYMHnet can provide results for both data and model uncertainty quantification, whereas the related methods cannot.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Experimental observations of detached bow shock formation in the interaction of a laser-produced plasma with a magnetized obstacle

The magnetic field produced by planets with active dynamos, like the Earth, can exert sufficient pressure to oppose supersonic stellar wind plasmas, leading to the formation of a standing bow shock upstream of the magnetopause, or pressure-balance surface. Scaled laboratory experiments studying the interaction of an inflowing solar wind analog with a strong, external magnetic field are a promising new way to study magnetospheric physics and to complement existing models, although reaching regimes favorable for magnetized shock formation is experimentally challenging. This paper presents experimental evidence of the formation of a magnetized bow shock in the interaction of a supersonic, super-Alfvenic plasma with a strongly magnetized obstacle at the OMEGA laser facility. The solar wind analog is generated by the collision and subsequent expansion of two counterpropagating, laser-driven plasma plumes. The magnetized obstacle is a thin wire, driven with strong electrical currents. Hydrodynamic simulations using the FLASH code predict that the colliding plasma source meets the criteria for bow shock formation. Spatially resolved, optical Thomson scattering measures the electron number density, and optical emission lines provide a measurement of the plasma temperature, from which we infer the presence of a fast magnetosonic shock far upstream of the obstacle. Proton images provide a measure of large-scale features in the magnetic field topology, and reconstructed path-integrated magnetic field maps from these images suggest the formation of a bow shock upstream of the wire and as a transient magnetopause. Finally, we compare features in the reconstructed fields to two-dimensional MHD simulations of the system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Simulating ‘Two Ribbon’ Type Solar Flares [Slides]

The underlying mechanism in solar flares in a process known as magnetic reconnection. This astrophysical process is when magnetic field lines, running anti-parallel, break and reconnect. The change in configuration of field lines results in an explosive release of energy as the leftover magnetic energy is converted to kinetic and thermal energies. In this project, we are using an astrophysical magnetohydrodynamic (MHD) simulation code known as Athena++ with a reconnection problem generator file created by Li et al. 2018. Our current research is to successfully implement a radiative cooling term into the MHD equations as it could have important physical effects on the plasma. We use Klimchuk et al. 2008 and SPEX_DM as our chosen cooling functions. The results from the SPEX_DM function show there is a condensation forming that we had predicted but had not seen before with our simulation code. We will continue to analyze the SPEX_DM function and potentially implement thermal conduction.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Experimental observations of detached bow shock formation in the interaction of a laser-produced plasma with a magnetized obstacle

The magnetic field produced by planets with active dynamos, like the Earth, can exert sufficient pressure to oppose supersonic stellar wind plasmas, leading to the formation of a standing bow shock upstream of the magnetopause, or pressure-balance surface. Scaled laboratory experiments studying the interaction of an inflowing solar wind analog with a strong, external magnetic field are a promising new way to study magnetospheric physics and to complement existing models, although reaching regimes favorable for magnetized shock formation is experimentally challenging. This paper presents experimental evidence of the formation of a magnetized bow shock in the interaction of a supersonic, super-Alfvenic plasma with a strongly magnetized obstacle at the OMEGA laser facility. The solar wind analog is generated by the collision and subsequent expansion of two counter- propagating, laser-driven plasma plumes. The magnetized obstacle is a thin wire, driven with strong electrical currents. Hydrodynamic simulations using the FLASH code predict that the colliding plasma source meets the criteria for bow shock formation. Spatially resolved, optical Thomson scat- tering measures the electron number density, and optical emission lines provide a measurement of the plasma temperature, from which we infer the presence of a fast magnetosonic shock far upstream of the obstacle. Proton images provide a measure of large-scale features in the magnetic field topology, and reconstructed path-integrated magnetic field maps from these images suggest the formation of a bow shock upstream of the wire and as a transient magnetopause. We compare features in the reconstructed fields to two-dimensional MHD simulations of the system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015

Two of the largest geomagnetic storms of the last decade were witnessed in 2015. On 17 March 2015, a coronal mass ejection-driven event occurred with a Dst (storm time ring current index) value reaching –223 nT. On 22 June 2015 another strong storm (Dst reaching –204 nT) was recorded. These two storms each produced almost total loss of radiation belt high-energy (E ≳ 1 MeV) electron fluxes. Following the dropouts of radiation belt fluxes there were complex and rather remarkable recoveries of the electrons extending up to nearly 10 MeV in kinetic energy. The energized outer zone electrons showed a rich variety of pitch angle features including strong “butterfly” distributions with deep minima in flux at α = 90°. However, despite strong driving of outer zone earthward radial diffusion in these storms, the previously reported “impenetrable barrier” at L ≈ 2.8 was pushed inward, but not significantly breached, and no E ≳ 2.0 MeV electrons were seen to pass through the radiation belt slot region to reach the inner Van Allen zone. Altogether, these intense storms show a wealth of novel features of acceleration, transport, and loss that are demonstrated in the present detailed analysis.

58 GEOSCIENCES↗