Search NASA⌕ Search

SEARCH · Search NASA

Results for “Corona Dynamics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

MHD simulations of coronal mass ejections - Importance of the driving mechanism

The importance of the form of the driving mechanism in MHD simulations of coronal mass ejections is investigated. A model simulation problem is devised, and it is found that the use of a simple form for the initial corona, with an upward moving parcel of cold, dense plasma as the driving mechanism, can produce results that are consistent with many of the features observed by coronagraphs. The results imply that the nature of the driving mechanism may play an important role in determining the dynamical evolution of mass ejections.

Linker, J. A.↗
NASA NTRS2000

Fine Structure in the Corona and Solar Wind at High Heliographic Latitudes at Solar Maximum

Microstreams and pressure balance structures in fast solar wind were more easily detected at Ulysses at 2.2 AU over the poles than at Helios at 0.3 AU. This is because solar rotation brings sources of fast solar wind beneath sources of slow solar wind at a rate that depends on latitude, for the same size features. Dynamic interaction between the fast and slow wind tends to mix the flows and make features more difficult to detect with increasing distance from the Sun. A given sized feature takes proportionally longer to pass a longitude when it is at 80 degrees latitude than when it is at the equator. At solar maximum, Ulysses will mainly be sampling solar wind coming from above streamers and from near streamers. The data will provide information on fine structure at the tops of streamers - the stalks - and on the source of slow solar wind, The visibility of the boundaries between fast and slow wind and of the stalk will increase with increasing latitude. We will present quantitative calculations of the visibility of various sized features, with various differences in flow speed, at the location of Ulysses when it is over the south (in 2000) and north (in 2001) polar regions of the Sun.

Suess. S. T.↗
NASA NTRS2001

Fine Structure in the Corona and Solar Wind at High Heliographic Latitudes at Solar Maximum

Microstreams and pressure balance structures in fast solar wind were more easily detected at Ulysses at 2.2 AU over the poles than at Helios at 0.3 AU. This is because solar rotation brings sources of fast solar wind beneath sources of slow solar wind at a rate that depends on latitude, for the same size features. Dynamic interaction between the fast and slow wind tends to mix the flows and make features more difficult to detect with increasing distance from the Sun. A given sized feature takes proportionally longer to pass a longitude when it is at 80 degrees latitude than when it is at the equator. At solar maximum, Ulysses will mainly be sampling solar wind coming from above streamers and from near streamers. The data will provide information on fine structure at the tops of streamers - the stalks - and on the source of slow solar wind. The visibility of the boundaries between fast and slow wind and of the stalk will increase with increasing latitude. I will present quantitative calculations of the visibility of various sized features, with various differences in flow speed, at the location of Ulysses when it is over the south (in 2000) and north (in 2001) polar regions of the Sun.

Suess, S. T.↗
NASA NTRS2008

Coronal Mass Ejections and their Implications for the Corona and Heliosphere

Coronal mass ejections (CMEs) are the largest and most energetic form of transients that connect the Sun to the heliosphere. They are critically important both for understanding the physical mechanisms of explosive solar activity and for predicting space weather. Furthermore they are an extreme example of how cross-scale coupling can play a critical role in determining the properties of a large-scale dynamical system. In this presentation CME theories are reviewed and the latest results from 3D numerical modeling of CME initiation propagation to the heliosphere are presented. In particular the focus is on the breakout model, but many of the results hold for the flux rope models as well. The implications of these results for understanding heliospheric structure and dynamics and for upcoming space missions will be discussed.

Antiochos, Spiro K.↗
NASA NTRS1982

Solar atmospheric dynamics. II - Nonlinear models of the photospheric and chromospheric oscillations

The one-dimensional, nonlinear dynamics of the solar atmosphere is investigated, and models of the observed photospheric (300 s) and chromospheric (200 s) oscillations are described. These are resonances of acoustic wave cavities formed by the variation of the temperature and ionization between the subphotospheric, hydrogen convection zone and the chromosphere-corona transition region. The dependence of the oscillations upon the excitation and boundary conditions leads to the conclusion that for the observed amplitudes, the modes are independently excited and, as trapped modes, transport little if any mechanical flux. In the upper photosphere and lower chromosphere, where the two modes have comparable energy density, interference between them leads to apparent vertical phase delays which might be interpreted as evidence of an energy flux.

Leibacher, J.↗
NASA NTRS1994

Radio evidence for nonthermal particle acceleration on stars of late spectral type

Radio evidence for nonthermal particle acceleration on stars of late spectral type (G, K, and M) is reviewed, including the pre-main-sequence T Tauri stars, the dwarf M flare stars, and the RS CVn binary stars. Both the long-lasting radio emission and the transient radio flares can be attributed to nonthermal electrons accelerated in magnetically confined coronae, radiating by either incoherent gyrosynchrotron radiation or by coherent processes. Related observations of the Sun provide the framework for interpreting the radio emission of late-type stars. We review recent Very Long Base Interferometry (VLBI) observations of single and binary stars, observations of rapid acceleration and dynamic spectra of dwarf M flare stars, and models for long-lasting radio emission from dwarf M flare stars and RS CVn stars. The VLBI data provide evidence for nonthermal particle acceleration in large-scale magnetospheres several times larger than the stellar radius for T Tauri and RS CVn stars. In contrast, rapid radio flares on dwarf M stars require sources much smaller than the visible star in size, and this is consistent with the VLBI data. Dynamic spectra suggest particle acceleration by relativistic electron beams on dwarf M stars. The long-lived radio radiation of dwarf M stars and RS CVn stars requires more-or-less continuous particle acceleration over periods of hours, perhaps by persistent low-amplitude flaring.

Lang, Kenneth R.↗
NASA NTRS2019

The SDO/EVE Solar Irradiance Coronal Dimming Index Catalog. I. Methods and Algorithms

When a coronal mass ejection departs, it leaves behind a temporary void. That void is known as coronal dimming, and it contains information about the mass ejection that caused it. Other physical processes can cause parts of the corona to have transient dimmings, but mass ejections are particularly interesting because of their influence in space weather. Prior work has established that dimmings are detectable even in disk-integrated irradiance observations, i.e., Sun-as-a-star measurements. The present work evaluates four years of continuous Solar Dynamics Observatory Extreme Ultraviolet Experiment (EVE) observations to greatly expand the number of dimmings we may detect and characterize, and collects that information into James’s EVE Dimming Index catalog. This paper details the algorithms used to produce the catalog, provides statistics on it, and compares it with prior work. The catalog contains 5051 potential events (rows), which correspond to all robustly detected solar eruptive events in this time period as defined by >C1 flares. Each row has a corresponding 27,349 elements of metadata and parameterizations (columns). In total, this catalog is the result of analyzing 7.6 million solar ultraviolet light curves.

James’s EVE Dimming Index (JEDI)↗
DOE OSTI2021

Molecular Weight Dependence of Block Copolymer Micelle Fragmentation Kinetics

The effect of molecular weight (M) on the fragmentation kinetics of micelles formed by 1,2-polybutadiene-block-poly(ethylene oxide) (PB-PEO) copolymers was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A series of six samples, with total M ranging from 10 4 to 10 5 g mol –1 and nearly constant composition (f PEO ≈ 0.4), were examined; all six formed spherical micelles with PEO coronas. Nonequilibrium PB-PEO micelles were prepared by direct dissolution, a process that systematically produces nanoparticles with mean aggregation numbers more than twice the equilibrium values. When subjected to high temperature annealing (170 °C), the average micelle radius was found to decrease substantially, as determined by temperature-jump dynamic light scattering (T-jump DLS) and time-resolved small-angle X-ray scattering (TR-SAXS). Furthermore, the characteristic fragmentation times (τ) were found to increase strongly with increasing degree of polymerization N, as τ ~ N 1.8 . This result compares favorably with the prediction of a previously untested model.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1990

Filament cooling and condensation in a sheared magnetic field

Thermal instability driven by optically thin radiation in the corona is believed to initiate the formation of solar filaments. The fact that filaments are observed generally to separate regions of opposite, line-of-sight, magnetic polarity in the differentially rotating photosphere suggests that filament formation requires the presence of a highly sheared magnetic field. The coupled energetics and dynamics of the most important condensation modes, those due to perpendicular thermal conduction at short wavelengths are discussed. Linear structure in the sheared field and their growth rates is described, and 2D, nonlinear, MHD simulations of the evolution of these modes in a force-free field are conducted. The simulations achieve the fine thermal structures, minimum temperatures and maximum densities characteristic of observed solar filaments.

Van Hoven, Gerard↗
NASA NTRS2008

The Formation of Coronal Loops by Thermal Instability in Three Dimensions

Plasma loops in solar active regions have been observed in EUV and soft X-rays for decades. Their formation mechanism and properties, however, are still not fully understood. Predictions by early models, based on 1D hydrostatic equilibria with uniform plasma heating, are not consistent with high-resolution measurements. In this Letter, we demonstrate, via 3D simulations, that a class of heating models can lead to the dynamic formation of plasma loops provided the plasma is heated sufficiently to match SXT soft X-ray measurements. We show that individual flux tubes in a 3D magnetic structure tend to stand out against their neighbors. The loops have large aspect ratios and nearly uniform cross sections in the corona, similar to those observed by EIT and TRACE. The coronal EUV emission from these thermally unstable solutions is roughly consistent with EIT measurements. The solution oscillates in time through a large-amplitude, nonlinear cycle, leading to repeated brightening and fading of the loops.

Mok, Yung↗
NASA NTRS2017

Solar Magnetic Activity and Solar-Stellar Connections

Prediction of solar magnetic activity on various temporal scales is a fundamental element of space weather, which requires a wide range of theoretical and observational expertise in solar phenomena from the deep interior to the corona. Historical observations have revealed many features of cyclic variations of the solar activity; but these data are dramatically insufficient to draw a physical picture of global magnetic field evolution. New observational data, currently available from space missions and ground-based observatories, provide us with detailed information about solar dynamics and magnetism. However, because of the relatively short duration of data series and the great variety of data types and quality, it is challenging to assimilate these data in theoretical models and make reliable forecasts. The recent unexpectedly weak solar activity cycles, as well as observations of rotational and magnetic topology transitions in solar-type stars, suggest that the Sun and its magnetic dynamo are currently in a very interesting evolutionary stage. This could relate to the difficulty in getting a model of the Sun to produce solar-like – rather than anti-solar-like – differential rotation, to reproduce the rotation profile obtained from helioseismology, and to predict solar activity cycles.

magnetic↗
NASA NTRS1980

Mass ejections

Observations and model simulations of solar mass ejection phenomena are examined in an investigation of flare processes. Consideration is given to Skylab and other observations of flare-associated sprays, eruptive prominences, surges and coronal transients, and to MHD, gas dynamic and magnetic loop models developed to account for them. Magnetic forces are found to confine spray material, which originates in preexisting active-region filaments, within steadily expanding loops, while surges follow unmoving, preexisting magnetic field lines. Simulations of effects of a sudden pressure pulse at the bottom of the corona are found to exhibit many characteristics of coronal transients associated with flares, and impulsive heating low in the chromosphere is found to be able to account for surges. The importance of the magnetic field as the ultimate source of energy which drives eruptive phenomena as well as flares is pointed out.

Rust, D. M.↗
DOE OSTI2026

Modeling The Nucleosynthetic Imprint of Stellar Merger Phenomena - Final Technical Report

This DOE CAREER project developed a comprehensive, multi-physics framework for modeling stellar mergers and their observable consequences. The work successfully integrated analytical models, three-dimensional hydrodynamic simulations, stellar evolution calculations, nucleosynthesis, and radiation transport into a unified pipeline. Key scientific advances include demonstrating stellar mergers as a unifying explanation for systems such as Betelgeuse and R Coronae Borealis stars, quantifying merger-driven chemical signatures, and establishing the connection between merger physics and circumstellar environments. A major outcome of the project is the development of SuperLite, an open-source Monte Carlo radiation transport code that enables the generation of synthetic spectra for astrophysical transients. This work bridges dynamical, thermal, and radiative timescales and provides a powerful, DOE-relevant computational framework for interpreting observations of supernovae and related transient phenomena, while also contributing to workforce development through the training of postdoctoral researchers and graduate students.

Chatzopoulos, Emmanouil [Louisiana State Universit↗
NASA NTRS1996

On flow phenomena that emit X-rays in hot star winds

The X-ray emission from O stars may originate from instability-generated shocks in their stellar winds. Previous numerical simulations that assumed the wind to be isothermal could only draw limited conclusions concerning this emission. Calculations that include the energy transfer in the wind are presented. They confirm that up to a few stellar radii, radiative cooling is efficient which implies that the shock cooling zones are short in comparison with the dynamical lengths. At larger radii, the wind structure changes as all the shocks are destroyed due to a broadening of their cooling zones. The following flow phenomena are discussed as possible X-ray sources: inner radiative shock; shock merging, outer adiabatic shocks, remaining hot gas from shock destruction, and an outer corona.

Feldmeier, A.↗
NASA NTRS2003

The Formation of Relativistic Jets from Kerr Black Holes

We have performed the first fully three-dimensional general relativistic magnetohydrodynamics (GRMHD) simulation for Schwarzschild and Kerr black holes with a free falling corona and thin accretion disk. The initial simulation results with a Schwarzschild metric show that a jet is created as in the previous axisymmetric simulations with mirror symmetry at the equator. However, the time to form the jet is slightly longer than in the 2-D axisymmetric simulation. We expect that the dynamics of jet formation are modified due to the additional freedom in the azimuth dimension without axisymmetry with respect to the Z axis and reflection symmetry respect to the equatorial plane. The jet which is initially formed due to the twisted magnetic fields and shocks becomes a wind at the later time. The wind flows out with a much wider angle than the initial jet. The twisted magnetic fields at the earlier time were untwisted and less pinched. The accretion disk became thicker than the initial condition. Further simulations with initial perturbations will provide insights for accretion dynamics with instabilities such as magneto-rotational instability (MRI) and accretion-eject instability (AEI). These instabilities may contribute to variabilities observed in microquasars and AGN jets.

Nishikawa, K.-I.↗
NASA NTRS2018

Helioseismic Observations of Torsional Oscillations Inside the Sun and Their Potential for Predicting Solar Cycles

The helioseismic analysis of torsional oscillations of the Sun, obtained in 1996-2018 from SOHO (Solar and Heliospheric Observatory) and SDO (Solar Dynamics Observatory), reveals the spatio-temporal dynamics associated with the dynamo process. The data reveal new relationships between the migrating magnetic field patterns observed in synoptic magnetograms and the dynamics of torsional oscillations near the surface and in the interior. In particular, it is found that the evolution of torsional oscillations in the deep convection zone is ahead of the surface magnetic evolution by several years, and that it is related to the extended solar cycle phenomenon previously observed in the solar corona. The data show substantial differences in the torsional oscillation properties between Cycles 23 and 24 indicating fundamental changes in the dynamo regime, and also reveal initiation of Cycle 25. The helioseismology observations of the torsional oscillations open new perspectives for understanding the global dynamo processes inside the Sun, and for predicting the next solar cycle.

Oscillations↗
NASA NTRS2020

Transition Region Contribution to AIA Observations in the Context of Coronal Heating

We investigate the ratio of coronal and transition region intensity in coronal loops observed by the AtmosphericImaging Assembly(AIA)on the Solar Dynamics Observatory(SDO). Using Enthalpy-based Thermal Evolution ofLoops(EBTEL)hydrodynamic simulations, we model loops with multiple lengths and energyfluxes heatedrandomly by events drawn from power-law distributions with different slopes and minimum delays between eventsto investigate how each of these parameters influences observable loop properties. We generate AIA intensitiesfrom the corona and transition region for each realization. The variations within and between models generatedwith these different parameters illustrate the sensitivity of narrowband imaging to the details of coronal heating.We then analyze the transition region and coronal emission from a number of observed active regions andfindbroad agreement with the trends in the models. In both models and observations, the transition region brightness issignificant, often greater than the coronal brightness in all six“coronal”AIA channels. We also identify an inverserelationship, consistent with heating theories, between the slope of the differential emission measure(DEM)coolward of the peak temperature and the observed ratio of coronal to transition region intensity. These resultshighlight the use of narrowband observations and the importance of properly considering the transition region ininvestigations of coronal heating

S J Schonfeld↗
NASA NTRS1987

Meterwave observations of a coronal hole

Meter-wave maps are presented showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in HeI lambda10830 spectroheliograms. The 73.8 MHz coronal hole, when seen near disk center, appears to coincide with the HeI footprint of the hole. At the lower frequencies, the emission comes from higher levels of the corona, and the hole appears to be displaced, probably due to the non-radial structure of the coronal hole. The contrast of the hole relative to the quiet Sun is much greater than reported previously for a coronal hole observed at 80 MHz. The higher contrast is certainly real, due to the superior dynamic range, sensitivity, and calibration of the Clark Lake instrument. Using a coronal hole model, the electron density is derived from radio observations of the brightness temperature. A very large discrepancy is found between the derived density and that determined from Skylab EUV observations of coronal holes. This discrepancy suggests that much of the physics of coronal holes has yet to be elucidated.

Wang, Z.↗