Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SOLAR ATMOSPHERE”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Effects of diffusion and mass flows on C IV and Si IV lines formed in the solar atmosphere

A model for the transition region is derived from an initial interpretation of EUV observations, assuming ionization equilibrium and constant elemental abundance with height. The effects of diffusion and mass flows are then included in the initial model and the emergent profiles of several C IV and Si IV lines are computed. It is found that diffusion and mass flows have a strong effect on both the emergent intensity and spectral shape of these lines. Diffusion acts to deplete the transition region of heavy ions to an extent which depends on the detailed temperature and density structure. The net effect is a weighting of the coronal emission relative to that in the transition. On the basis of the results, it is suggested that the downflows observed in the network in lines of C IV and Si IV could be due to gravitational settling of the ions following their injection, via diffusion, into the corona from spicules. When flows are superposed on the basic diffusion model, the rapid change in elemental abundance characteristic of the model is virtually eliminated and the coronal contribution to the emission in C IV and Si IV lines becomes negligible relative to that in the transition region. Flows have a strong effect on the computed line intensities and introduce large asymmetries into the line shapes.

Roussel-Dupre, R.↗
NASA NTRS1982

The vertical propagation of waves in the solar atmosphere. II Phase delays in the quiet chromosphere and cell-network distinctions

The differences in the phase of the velocity oscillations between a pair of chromospheric Ca II lines was measured using the Vacuum Tower Telescope at the Sacramento Peak Observatory. The observed phase differences indicate that the acoustic modes are trapped or envanescent, rather than propagating, in the chromosphere. Systematic distinctions are found in the phase delays between quiet network and cell interior regions for both intensity and velocity oscillations in photospheric and chromospheric lines. The theory of linear perturbations in an isothermal atmosphere is invoked to interpret these differences. From this analysis it is found that one or more of the following explanations is possible: (1) the radiative damping is more effective in the network than in the cell interior; (2) the network features exclude oscillations of large horizontal wavenumber; or (3) the scale height of the chromosphere is larger in the network than in the cell interior.

Lites, B. W.↗
NASA NTRS1986

Magnetic energy storage and conversion in the solar atmosphere

According to the approach employed in this investigation, particularly important simple configurations of magnetic field and plasma are identified, and it is attempted to achieve an understanding of the large-scale dynamic processes and transformations which these systems can undergo. Fundamental concepts are discussed, taking into account aspects of magnetic energy generation, ideal MHD theory, non-MHD properties, the concept of 'anomalous' resistivity, and global electrodynamic coupling. Questions of magnetically controlled energy conversion are examined, giving attention to magnetic modifications of plasma transport, the transition region structure and flows, channeling and acceleration of plasma, channeling and dissipation of MHD waves, and anomalous dissipation of field-aligned currents. A description of the characteristics of magnetohydrodynamic energy conversion is also provided, and outstanding questions are discussed.

Spicer, D. S.↗
NASA NTRS1986

The energy balance of plasmoids in the solar atmosphere

The properties of an isolated magnetized plasmoid in a nonuniform magnetic field such as arises in stellar atmospheres are studied. The work of Pneuman and Cargill (1985) on the so-called melon-seed effect is extended to include an equation describing the energy balance, so giving a unified picture of the shape, motion, and energetics of the plasmoid. Three treatments of plasmoid energy balance are considered: (1) a polytropic law, (P = about N to the gamma); (2) one in which the plasmoid cools radiatively; and (3) one in which a heating function proportional to the local density balances the radiation. For a gamma = 4/3 polytrope the evolution is self-similar, so that the plasmoid maintains its shape as it moves out from the stellar surface. If gamma is less than 4/3, the final shape is a long thin cigar-shaped body, whereas if gamma is greater than or equal to 4/3, it ultimately becomes self-similar. In cases with radiation and also with heating, the ultimate shape of the plasmoid is determined by whether its gas or magnetic pressure dominate. The former is equivalent to the gamma-less-than-4/3 polytrope, and the latter to the gamma-greater-than-4/3 one. If radiation alone is present, the plasmoid cools rapidly and subsequently evolves self-similarly. If heating balances radiation initially, then the plasmoid heats up as it moves out, but, if the ratio of the transit of time of Alfven waves across it is much less than the radiative cooling time, it ultimately evolves as a gamma = 5/3 polytrope. In each case the plasmoid can be ejected to large distances (several radii) in a stellar atmosphere, for a reasonable choice of surface parameters.

Cargill, P. J.↗
NASA NTRS1987

The formation of current sheets in the solar atmosphere

A simple model of the effect of slow photospheric motions on the coronal magnetic field is examined. In this model, a magnetic field is stretched between two conducting plates and slow tangential displacements of the plates cause the field to evolve quasi-statically. If the field is treated as a continuum, the interior magnetic topology is uniquely specified by the displacement of the boundaries, while the topology of a field made up of discrete flux tubes is not determined by the boundary displacement. Treating the field as a continuum, it is found that small perturbations of a constant vertical or weakly sheared field can come to an equilibrium free of singularities if the separation between the plates is finite.

Zweibel, Ellen G.↗
NASA NTRS1990

A comparison between progressive extension method (PEM) and iterative method (IM) for magnetic field extrapolations in the solar atmosphere

This paper presents a comparison between two numerical methods for the extrapolation of nonlinear force-free magnetic fields, viz the Iterative Method (IM) and the Progressive Extension Method (PEM). The advantages and disadvantages of these two methods are summarized, and the accuracy and numerical instability are discussed. On the basis of this investigation, it is claimed that the two methods do resemble each other qualitatively.

Wu, S. T.↗
NASA NTRS1991

Electric fields in the solar atmosphere - A review

A review is presented of remote sensing techniques which measure the electric field component transverse to the line of sight and achieve a sensitivity range of 5-10 V/cm. Three models are shown to predict quasistatic, macroscopic values of E(parallel), the electric field component parallel to the magnetic vector, beyond the sensitivity range considered. These processes are: the discharge model of flares; the models of return currents related to flare particle beams; and the models of neutral sheets related to two-ribbon flares and postflare loops. Time dependent electric fields related to MHD and plasma waves, and to plasma disturbance, may allow the detection of both E components (parallel and perpendicular). The uncertainty relating to the emission measures, time scales, volumes, and plasma conditions of these flares and electrified plasma volumes is emphasized. It is pointed out, however, that important information can be obtained by observing electric fields at existing sensitivity levels. By measuring these E-fields, the understanding of flares and related dynamic events can be improved.

Foukal, P.↗
NASA NTRS1991

Formation of the infrared emission lines of Mg I in the solar atmosphere

A non-LTE radiative transfer investigation of the emission lines is conducted at 7 and 12 microns using a realistic atomic model for neutral magnesium. An average quiet sun atmospheric model is used to calculate emission-line profiles that resemble the observed ones, i.e., broad absorption troughs with narrow central emission, and significant limb brightening. The charge exchange rates are found to be significant, but the effects of high-n coupling between Mg and Mg(+) together with radiative low-n transitions are of greater importance. It is confirmed that the emission cores are formed no higher than the temperature minimum region, and that the emission is caused by non-LTE effects rather than by the chromospheric temperature rise. It is inferred from the model calculations that the line core is sensitive to magnetic fields located almost 400 km above those measured in ordinary magnetograms; the gas pressure decreases 20-fold between these two heights.

Chang, E. S.↗
NASA NTRS1992

Plasma dynamics and energetics in the solar atmosphere

Prominence condensation and support, the dynamics of coronal loops, and streamer structure and disconnection are briefly discussed. Prominence condensation and magnetic levitation in a coronal loop and simulations of coronal disconnection events are discussed.

Vanhoven, Gerard↗
NASA NTRS1992

The thermal and plasma-physical evolution of laminar current sheets formed in the solar atmosphere by emerging flux

A time-dependent analysis of emerging flux is carried out, and the time evolution of both the current sheet energetics and the plasma state is calculated. This evolution is determined in two different regimes. In the first case the width of the current sheet is assumed to be independent of the sheet thermodynamics and is fixed by the initial conditions. In the second, the width of the current sheet is a function of the resistivity and is allowed to decrease to its minimum given by the electron gyroradius. In both cases the resistivity is computed according to the marginal stability hypothesis. In each case the thermodynamic evolution is found to be quite rapid, with the temperature increasing from 10,000 to 1,000,000 K in a second or less. In contrast to previous studies, it is found that the resistivity is not significantly enhanced by the current-driven plasma wave turbulence. It is concluded that a laminar current sheet cannot be responsible for the activity associated with emerging flux.

Larosa, T. N.↗
NASA NTRS2009

The Lower Solar Atmosphere During the WHI Campaign (20 Apr-16 May 2008)

The Whole Heliospheric Interval (WHI) period of 20 March - 16 April had a "quiet side" of the Sun, and an "active side," with three ARs. At least two of the ARs produced CMEs, but there were several events that may have been "confined eruptions" from these regions too. Examining the magnetic environment of the erupting regions gives insight into the onset and dynamics of the eruptions. Several of the CMEs can be traced back to likely disk sources, but several unmatched cases still remain. More work is needed to sort through these points.

Sterling, Alphonse↗
NASA NTRS2012

The Role of Type II Spicules in the Upper Solar Atmosphere

We examine the suggestion that most of the hot plasma in the Sun's co rona comes from type II spicule material that is heated as it is ejected from the chromosphere. This contrasts with the traditional view th at the corona is filled via chromospheric evaporation that results fr om coronal heating. We explore the observational consequences of a hy pothetical spicule dominated corona and conclude from the large discr epancy between predicted and actual observations that only a small fraction of the hot plasma can be supplied by spicules (<2% in active regions and <5% in the quiet Sun). The red- blue asymmetries of EUV spec tral lines and the ratio of lower transition region (LTR; T< or =0.1 MK) to coronal emission measures are both predicted to be 2 orders of magnitude larger than observed. Furthermore, hot spicule material would cool dramatically by adiabatic expansion as it rises into the corona, so coronal heating would be required to maintain the high temperatu res that are seen at all altitudes. The necessity of coronal heating is inescapable. Traditional coronal heating models predict far too little emission from the LTR, and we suggest that this emission comes pr imarily from the bulk of the spicule material that is heated to < or =0.1 MK and is visible in He II (304 ?A) as it falls back to the surf ace.

Klimchuk, James A.↗
NASA NTRS2019

IRIS Observations of Magnetic Interactions in the Solar Atmosphere Between Preexisting and Emerging Magnetic Fields. II. UV Emission Properties

Multiwavelength ultraviolet (UV) observations by the Interface Region Imaging Spectrograph satellite in active region NOAA 12529 have recently pointed out the presence of long-lasting brightenings, akin to UV bursts, and simultaneous plasma ejections occurring in the upper chromosphere and transition region during secondary flux emergence. These signatures have been interpreted as evidence of small-scale, recurrent magnetic reconnection episodes between the emerging flux region (EFR) and the preexisting plage field. Here we characterize the UV emission of these strong, intermittent brightenings and study the surge activity above the chromospheric arch filament system (AFS) overlying the EFR. We analyze the surges and the cospatial brightenings observed at different wavelengths. We find an asymmetry in the emission between the blue and red wings of the Si iv λ1402 Å and Mg ii k λ2796.3 lines, which clearly outlines the dynamics of the structures above the AFS that form during the small-scale eruptive phenomena. We also detect a correlation between the Doppler velocity and skewness of the Si iv λλ1394 and 1402 line profiles in the UV burst pixels. Finally, we show that genuine emission in the Fe xii λ1349.4 line is cospatial to the Si iv brightenings. This definitely reveals a pure coronal counterpart to the reconnection event.

Guglielmino, Salvo L.↗