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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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NASA NTRSDate not supplied

Preliminary Results from the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket mission that aims to observe the soft x-ray solar spectrum (0.6 – 2.5 nm) with both spatial and spectral resolution over a substantial field of view. This wavelength range has several high temperature and abundance diagnostics that can be used to assist in diagnosing the coronal heating mechanism. MaGIXS launched from White Sands Missile Range on July 30, 2021 and successfully observed the Sun through a 4’ x 33’ effective slot, producing ``overlappograms’’, where the spatial and spectral information are overlapped and must be unfolded. In this presentation, I will report on the MaGIXS launch and data collection and provide preliminary analysis of MaGIXS data.

Amy Winebarger↗
NASA NTRSDate not supplied

Preliminary Results from the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket mission that aims to observe the soft x-ray solar spectrum (0.6 – 2.5 nm) with both spatial and spectral resolution over a substantial field of view. This wavelength range has several high temperature and abundance diagnostics that can be used to assist in diagnosing the coronal heating mechanism. MaGIXS launched from White Sands Missile Range on July 30, 2021 and successfully observed the Sun through a 4’ x 33’ effective slot, producing ``overlappograms’’, where the spatial and spectral information are overlapped and must be unfolded. In this presentation, I will report on the MaGIXS launch and data collection and provide preliminary analysis of MaGIXS data.

Amy Winebarger↗
NASA NTRS2001

Magnetic Characteristics of Active Region Heating Observed with TRACE, SOHO/EIT, and Yohkoh/SXT

Over the past several years, we have reported results from studies that have compared the magnetic structure and heating of the transition region and corona (both in active regions and in the quiet Sun) by combining X-ray and EUV images from Yohkoh and Solar and Heliospheric Observatory (SOHO) with photospheric magnetograms from ground-based observatories. Our findings have led us to the hypothesis that most heating throughout the corona is driven from near and below the base of the corona by eruptive microflares occurring in compact low-lying "core magnetic fields (i.e., fields rooted along and closely enveloping polarity inversion lines in the photospheric magnetic flux). We now extend these studies, comparing sequences of UV images from Transition Region and Coronal Explorer (TRACE) with longitudinal magnetograms from Kitt Peak and vector magnetograms from MUSIC. These comparisons confirm the previous results regarding the importance of core-field activity to active region heating. Activity in fields associated with satellite polarity inclusions and/or magnetically sheared configurations is especially prominent. This work is funded by NASA's Office of Space Science through the Sun-Earth Connection Guest Investigator Program and the Solar Physics Supporting Research and Technology Program.

Porter, J. G.↗
NASA NTRS1982

Collisional damping of surface waves in the solar corona

The damping of surface waves by viscosity and heat conduction is evaluated. For the solar corona, it is found that surface waves dissipate efficiently only if their periods are shorter than a few tens of seconds and only if the background magnetic field is less than about 10 Gauss. Heating of quiet coronal regions is possible if the coronal waves have short periods, but they cannot heat regions of strong magnetic field, such as coronal active region loops.

Gordon, B. E.↗
NASA NTRS2001

Characteristics of the Time Variable Component of the Coronal Heating Process

The goal of the proposed study was to explore the non-steady nature of the coronal heating processes and its manifestations in the inner corona and interplanetary space by coordinating coronal SOHO observations in white light, ultraviolet, and extreme ultraviolet, with complementary radio occultation measurements during an unprecedented and rare coincidence of a total solar eclipse with the superior conjunction of a planetary spacecraft, Galileo, in February 1998. In addition, radio occultation measurements by the Mars Global Surveyor spacecraft in May 1998 spanned the inner heliosphere observed by coronal SOHO instruments and probing it to within 0.5 R(sub S), above the solar surface. Inferences of physical properties derived from these simultaneous observations were subsequently used in solar wind model computations to yield the range of plasma parameters characteristic of the fast and slow solar wind.

Habbal, Shadia R.↗
NASA NTRS1984

The effect of line-tying on the radiative MHD stability of coronal plasmas with radial pressure profile

The role of photospheric line-tying, i.e., solar coronal loop structures, was investigated in terms of the effect on radiative modes and the influence that different radial pressure profiles exert on the effects of line-tying on radiative MHD stability. Energy is assumed dissipated by heat conduction and radiation and zero- and first-order solutions are obtained for the radiative time scales. Line-tying is a magnetic tension in the zero-order MHD mode and produces stability. Heat conduction occurs along bent field lines in first-order MHD modes when plasmas cross the field lines. Irradiated cool-core loops can experience MHD instabilities in the cylinder center, while line-tying can stabilize the plasma in the surrounding hot medium. Line-tying also adds stability to magnetosonic and condensation modes.

An, C.-H.↗
NASA NTRS1991

Data evaluation, analysis, and scientific study

Extensive work was performed in data analysis and modeling of solar active phenomena. The work consisted in the study of UV data from the Ultraviolet Spectrometer and Polarimeter (UVSP) instrument on board the Solar Maximum Mission satellite. These data were studied in conjunction with X-rays from the Hard X-ray Imaging Spectrometer (HXIS) instrument, and with H-alpha and magnetographic data from ground-based observatories. The processes we studied are the active phenomena which result from the interaction of the solar magnetic fields with the plasma in the outer regions of the solar atmosphere. These processes include some very dynamic processes such as the prominence eruptions and the 'microflares'. Our research aimed at characterizing the following: the observed phenomena, the possible physical models, and the relevance to the chromospheric and coronal heating.

Wu, S. T.↗
NASA NTRS1994

Electric currents and coronal heating in NOAA active region 6952

We examine the spatial and temporal relationship between coronal structures observed with the soft X-ray telescope (SXT) on board the Yohkoh spacecraft and the vertical electric current density derived from photospheric vector magnetograms obtained using the Stokes Polarimeter at the Mees Solar Observatory. We focus on a single active region: AR 6952 which we observed on 7 days during 1991 December. For 11 independent maps of the vertical electric current density co-aligned with non-flaring X-ray images, we search for a morphological relationship between sites of high vertical current density in the photosphere and enhanced X-ray emission in the overlying corona. We find no compelling spatial or temporal correlation between the sites of vertical current and the bright X-ray structures in this active region.

Metcalf, T. R.↗
NASA NTRS1989

H-alpha redshifts as a diagnostic of solar flare heating

The dynamics of chomospheric condensations formed during chromospheric evaporation are studied using coordinated X-ray and H-alpha observations of five solar flares. It is shown that the peak downflow velocity of condensations predicted by simple hydrodynamic compression of the chromosphere is in good agreement with empirical downflow velocities implied by impulsive phase H-alpha red wing Doppler shifts. It is found that the H-alpha wing redshift provides a diagnostic of the pressure excess in the evaporating region and the coronal energy flux driving chromospheric evaporation. Because preflare coronal pressures derived for each of the flares are high, it is suggested that the chromosphere succeeds in radiating excess flare heat energy without undergoing explosive chromospheric evaporation.

Zarro, Dominic M.↗
NASA NTRS1994

Flow properties of the solar wind obtained from white light data and a two-fluid model

The flow properties of the solar wind from 1 R(sub s) to 1 AU were obtained using a two fluid model constrained by density and scale height temperatures derived from white light observations, as well as knowledge of the electron temperature in coronal holes. The observations were obtained with the white light coronographs on SPARTAN 201-1 and at Mauna Loa (Hawaii), in a north polar coronal hole from 1.16 to 5.5 R(sub s) on 11 Apr. 1993. By specifying the density, temperature, Alfven wave velocity amplitude and heating function at the coronal base, it was found that the model parameters fit well the constraints of the empirical density profiles and temperatures. The optimal range of the input parameters was found to yield a higher proton temperature than electron temperature in the inner corona. The results indicate that no preferential heating of the protons at larger distances is needed to produce higher proton than electron temperatures at 1 AU, as observed in the high speed solar wind.

Habbal, Shadia Rifai↗
NASA NTRS1978

The solar probe and coronal dynamics

The discovery of coronal holes led to basic changes in ideas about the structure of the low corona and its expansion into the solar wind. The nature of the energy flux is not understood. Current ideas include enhanced thermal conductivities, extended MHD wave heating, and wave momentum transfer, all in rapidly diverging geometries. There is little feel for the relative importance of these processes. The Solar Probe, with its penetration deep into the solar corona, could lead to observational constraints on their relative importance, and thus to an understanding of the origin of the solar wind. Observations from the Solar Probe will also bear on such questions as to whether small scale "intrastream" structure is common close to the Sun in open field-line regions, whether the properties of the wind are pronouncedly different over closed and open field-line regions at five solar radii, and many others. The resolution of these questions requires measurements of the magnetic field and of the proton and electron distribution functions.

Belcher, J.↗
NASA NTRS1993

Solar flare model atmospheres

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

Hawley, Suzanne L.↗
NASA NTRS1973

Mass motion in solar flares

Mass motions in solar flares are here considered in terms of a previously proposed model. Particle acceleration occurs during reconnection of a current sheet located at coronal heights. The downward component of the particle flux produces an impulsive hard X-ray burst and heats the upper layers of the chromosphere sufficiently to lead to explosive evaporation. Some of the evaporated gas remains trapped in newly closed magnetic field lines and is responsible for the soft thermal component of X-ray emission. Gas which flows along open magnetic field lines subsequently forms a plasmoid which is ejected by magnetic stresses into interplanetary space and may subsequently cause a geomagnetic storm. Analysis of a highly simplified model leads to formulas for the density, temperature, and other parameters of the flare-produced plasma in terms of a length scale and mean magnetic field strength for the flare.

Sturrock, P. A.↗
NASA NTRS1994

Solar flare model atmospheres

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane-parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of nonthermal electrons and X-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick H I, Ca II and Mg II transitions using the non-local thermodynamic equilibrium (non-LTE) prescription in the program MULTI. Hydrogen ionization rates from X-ray photoionization and collisional ionization by nonthermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in the pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring. We have computed the chromospheric radiation that results from a range of coronal heating rates, with particular emphasis on the widely observed diagnostic H(alpha). Our conclusion is that the H(alpha) fluxes and profiles actually observed in flares can only be produced under conditions of a low-pressure corona with strong beam heating. Therefore we suggest that H(alpha) in flares is produced primarily at the footprints of newly heated loops where significant evaporation has not yet occurred. As a single loop evolves in time, no matter how strong the heating rate may become, the H(alpha) flux will diminish as the corona becomes denser and hence more effective at stopping the beam. This prediction leads to several observable consequences regarding the spatial and temporal signatures of the X-ray and H(alpha) radiation during flares.

Hawley, Suzanne L.↗
NASA NTRS2002

RHESSI and Trace Observations of the 21 April 2002 X1.5 Flare

Observations of the X1.5 flare on 21 April 2002 are reviewed using the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Transition Region and Coronal Explorer (TRACE). The major findings are as follows: 1. The 3-25 keV X-rays started 54 mins before the EUV (195 A) emission suggesting that the initial energy release heated plasma directly to 220 MK, well above the 1.6 MK needed to produce the Fe XII (195 A) line. 2. Using coaligned 12-25 keV RHESSI and TRACE images, further evidence is found for the existence of hot (15-20 MK) plasma in the 195 A passband. This hot, diffuse emission is attributed to the presence of the Fe XXIV (192 A) line within the TRACE 195 A passband. 3. The 12-25 keV source centroid moves away from the limb with an apparent velocity of approx. 9.9 km/ s, slowing to approx. 1.7 km/ s after 3 hours, its find altitude being approx. 120 Mm after approx. 12 hours. This suggests that the energy release site moves to higher altitudes in agreement with classical flare models. 4. The 50-100 keV emission correlates well with EUV flare ribbons, suggesting thick-target interactions at the footpoints of the magnetic arcade. The 50-100 keV time profile matches the time derivative of the GOES light curve (Neupert effect), which suggests that the same electrons that produced the thick-target hard X-ray emission also heat the plasma seen in soft X-rays. 5. X-ray footpoint emission has an E(sup -3) spectrum down to approx. 10 keV suggesting a lower electron cutoff energy than previously thought. 6. The hard X-ray (25-200 keV) peaks have FWHM durations of approx. 1 min suggesting a more gradual energy release process than expected. 7. The TRACE images reveal a bright symmetric front propagating away from the main flare site at speeds of greater than or = 120 km/ s. This may be associated with fast CME observed several minutes later by LASCO. 8. Dark sinuous lanes are observed in the TRACE images that extend almost radially from the post-flare loop system. This "fan of spines" becomes visible well into the decay phase of the flare and shows evidence for both lateral and downward motions.

Gallagher, Peter T.↗
NASA NTRS1992

Particle acceleration in solar flares - Observations

Contrary to our historical understanding, the energetic particles in most major solar proton events do not come from the flare itself. The particle abundances, ionization states, time evolution, and longitude distributions all indicate that the particles are accelerated from the ambient plasma by a shock wave driven by a coronal mass ejection in these events. In contrast, the particles that do come from impulsive solar flares are unique in character. These particles are electron rich, have He-3/He-4 enhancements of up to 10,000, and enhancements in heavy elements such as Fe/C by factors of 10. The high ionization state of Fe, +20 indicates that the material has been heated to temperatures of about 2 x 10 exp 7 K. It is generally believed that preferential heating by selective absorption of plasma waves is combined with stochastic acceleration in these events. Recent studies of the broad gamma-ray lines emitted by energetic particles within the flare loops indicate that they are also Fe-rich, He-3 rich and proton-poor like the particles seen at 1 AU. In large impulsive events, particles from the impulsive phase may be reaccelerated by a coronal blast-wave shock.

Reames, Donald V.↗
NASA NTRS1989

Creation of current filaments in the solar corona

It has been suggested that the solar corona is heated by the dissipation of electric currents. The low value of the resistivity requires the magnetic field to have structure at very small length scales if this mechanism is to work. In this paper it is demonstrated that the coronal magnetic field acquires small-scale structure through the braiding produced by smooth, randomly phased, photospheric flows. The current density develops a filamentary structure and grows exponentially in time. Nonlinear processes in the ideal magnetohydrodynamic equations produce a cascade effect, in which the structure introduced by the flow at large length scales is transferred to smaller scales. If this process continues down to the resistive dissipation length scale, it would provide an effective mechanism for coronal heating.

Mikic, Z.↗