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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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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Nearly sonic and transsonic convective motions in the solar atmosphere related to the solar wind origin

MHD equations are considered for the solar atmosphere. 15 different simplest MHD regimes are indicated for the momentum transport equation depending on the mutual binary interplay between 6 possible and locally dominant terms: non-stationarity and inhomogeneity of the flow, gas pressure, magnetic tensions, viscous and gravity forces. These regimes are delimited by five physically independent dimensionless parameters, for example, Strouhal, sonic Mach, alfvenic Mach, Reynolds and Froude numbers or their combinations. Another partially overlapping classification of the simplest regimes may be introduced based on the energy conservation equation. There are also 15 independent binary combinations between nonstationary and inhomogeneous convective terms, dissipative energy sinks and sources (viscous, heat-conductive, Joule and radiative ones) in the energy equation. More complicated regimes are considered with multiple dominated terms. All these MHD regimes play their important role somewhere in the solar atmosphere complicated by the tensor transport coefficients in the magnetically dominated regions of the upper atmosphere. Nearly sonic and transsonic nonstationary convective motions with ascending and descending flows are observed in the solar chromosphere. the transition region and the lower pans of the solar corona together with related horizontal velocity components. This convection represents a kind of the 'cocoonery' manufacturing nonstationary vortices generated here and partially connected to the photosphere and to the solar wind. The solar wind originates from this powerful transsonic muddle in the solar atmosphere as a tiny fraction of the streamlines which are temporarily getting detached from the 'cocoons; and going to the infinity. The topologically complicated instantaneous 'runaway surface' around the Sun, i.e., the surface which separates outgoing to the infinity streams from other finite flows in the solar atmosphere was not described in the literature and needs additional investigation. We conclude that a simple one-connected smooth and quasistationary 'critical surface' which is often supposed to be placed somewhere in the solar corona (say, at 4 solar radii) in reality does not exist. Observational and theoretical arguments favor instead of this a highly structured, disordered, patched and time-dependent sonic transition surface in the solar atmosphere permanently fluctuating at positional dependent heights starting sometimes from photospheric (and maybe subphotospheric) levels and more frequently from the chromosphenc network up to several solar radii in the solar corona.

Veselovsky, I. S.↗
NASA NTRS1973

A kinematic model of a solar flare.

Hyder advocated the idea that the optical (H-alpha) flares can be identified with the response of the solar chromosphere to an infalling material stream resulting from the 'disparition brusque' of a prominence. Since some flares are observed without any apparent association with infalling streams, in this paper we examine the possibility of identifying the optical flare with the response of the chromosphere to a supersonic disturbance, i.e., a shock, propagating downward. The undisturbed chromosphere is represented by the Harvard-Smithsonian Reference Atmosphere and the evolution of the shock is evaluated with the use of the CCW (Chisnell, Chester, Whitham) approximation based on the theory of characteristics. It is shown that the chromosphere is heated by the shock, that radiation is enhanced, and that the enhanced radiation terminates the shock around the height of the temperature minimum.

Nakagawa, Y.↗
NASA NTRS1974

Interplantetary streams and their interaction with the earth

Plasma and magnetic field observations of interplanetary streams near 1 AU are summarized. Two types of streams have been identified corotating streams and flare-associated, and other flow patterns are present due to interactions among streams. The theory of corotating streams, which attributes them to a high temperature region near the sun, satisfactorily explains many of the effects observed at 1 AU. A correspondingly complete theory of flare-associated streams does not exist. Streams are a key link in the chain that connects solar and geomagnetic activity. The factors that most influence geomagnetic activity are probably related to streams and determined by the dynamics of streams. The evolution of streams on scales of 27 days and 11 years probably determines the corresponding variations of geomagnetic activity.

Burlaga, L. F.↗
NASA NTRS1975

Interplanetary streams and their interaction with the earth

Plasma and magnetic field observations of interplanetary streams near 1 AU are summarized. Two types of streams have been identified - corotating streams and flare-associated, and other flow patterns are present due to interactions among streams. The theory of corotating streams, which attributes them to a high temperature region near the sun, satisfactorily explains many of the effects observed at 1 AU. A correspondingly complete theory of flare-associated streams does not exist. Streams are a key link in the chain that connects solar and geomagnetic activity. The factors that most influence geomagnetic activity are probably related to streams and determined by the dynamics of streams. The evolution of streams on scales of 27 days and 11 years probably determines the corresponding variations of geomagnetic activity.

Burlaga, L. F.↗
NASA NTRS1975

Measurements of large scale turbulence in the solar system

Direct observations of the solar wind between 1965 and 1972 indicate the existence of significant large scale (L is greater than 10 to the 6th km) turbulence in the solar system at heliocentric distances from 1 to 3 AU. These results are based on power spectra of the solar wind proton data obtained by plasma spectrometers on Pioneer 6 and Pioneer 10. The power spectra indicate that there is a power-law frequency dependence between 10 to the -4 Hz and 10 to the -3 Hz of the power spectra of the solar wind proton number density and streaming speed between 1 and 3 AU. The slopes and the amplitudes of the power spectra provide qualitative information concerning the cosmic ray diffusion tensor between 1965 and 1972 and at heliocentric distances between 1 AU and 3 AU.

Intriligator, D. S.↗
NASA NTRS1980

Trajectories and orbits from the NASA-NMSU Meteor Observatory. III

In this final of three papers from the NASA-NMSU Meteor Observatory, trajectory and orbital elements are reported for 13 doubly-photographed meteors, four of which are Geminids and one an Orionid. A pair of meteors with rather similar orbits suggests the possibility of a new stream active in the range of solar longitude 200 deg to 204 deg (13-18 October) with a radiant near delta Aurigae.

Drummond, J. D.↗
NASA NTRS1982

The photochemical heating of the cometary atmosphere

A self-consistent solution of the thermodynamic structure of an H2O-dominated multispecies cometary atmosphere at 1 AU is obtained by solving the simultaneous set of differential equations representing conservation of number density, momentum, energy, and the flux of solar UV radiation in the three streams responsible for the major photolytic processes. The relative efficiency of the expansion and infrared cooling by H2O over the photolytic heating by the UV radiation in the inner coma brings about a rapid decrease in the temperature there, reaching a minimum of only about 5.4 K at a nuclear distance of approximately 54 km. Thereafter, the temperature is found to increase to about 810 K at a nuclear distance of 25,000 km, owing to higher efficiency of the photolytic heating over the cooling process. The expansion in the inner coma is seen to be highly supersonic, attaining a maximum Mach number of about 15 at the distance of temperature minimum. After that, the Mach number steadily decreases, reaching a value of about 2.3 at a nuclear distance of 25,000 km.

Marconi, M. L.↗
NASA NTRS1983

Observational constraints on solar wind acceleration mechanisms

A complete theoretical understanding of the acceleration of the solar wind must account for at least three types of solar wind flow: high-speed streams associated with coronal holes, low-speed boundary layer flows associated with sector boundaries, and both high- and low-speed flows associated with impulsive ejections from the Sun. The properties of each type of flow are summarized.

Neugebauer, M.↗
NASA NTRS1983

Solar wind minor ions: Recent observations

Systematic studies show that the minor ions generally travel with a common bulk speed and have temperatures roughly proportional to their masses. It was determined that (3)He(++) content varies greatly; (3)He(++)/(4)He(++) ranges from as high as 10(-12) values to below 2 x 10(-4). In some solar wind flows which can be related to energetic coronal events, the minor ions are found in unusual ionization states containing Fe(16+) as a prominent ion, showing that the states were formed at unusually high temperatures. Unexpectedly, in a few flows substantial quantities of (4)He(+) were detected, sometimes with ions identifiable as O(2+) and O(3+). Surprisingly, in some of these examples the ionization state is mixed showing that part of the plasma escaped the corona without attaining the usual million-degree temperatures while other parts were heated more nearly in the normal manner. Additionally, detailed studies of the minor ions increased our understanding of the coronal expansion. For example, such studies contributed to identifying near equatorial coronal streamers as the source of solar wind flows between high speed streams.

Bame, S. J.↗
NASA NTRS1984

Ongoing data reduction, theoretical studies and supporting research in magnetospheric physics

Data from ISEE-3, Pioneer Venus Orbiter, and Voyager 1 and 2 were analyzed. The predictability of local shock macrostructure at ISEE-1, at the Earth's bow shock, from solar wind measurements made up-stream by ISEE-3, was conducted using computer graphic format. Morphology of quasi-parallel shock was reviewed. The review attempted to interrelate various measurements and computations involving the q-parallel structure and foreshock elements connected to it. A new classification for q-parallel morphology was suggested.

Scarf, F. L.↗
NASA NTRS1987

Collisionless coupling in the AMPTE artificial comet

Analysis of previously reported observations of the solar wind-barium interaction associated with the AMPTE artificial comet release of Dec. 27, 1984, is presented. On the basis of these results it is argued that solar wind couples momentum (and energy) to the barium ions through both laminar and turbulent processes. The laminar forces acting on the particles are the laminar electric and magnetic fields; the turbulent forces are associated with the intense electrostatic wave activity. This wave activity is shown to be caused by a cross-field solar wind proton-barium ion streaming instability. The observed wave frequencies and saturated amplitudes are consistent with the theoretical analysis.

Papadopoulos, K.↗
NASA NTRS2007

Regional Aerosol Optical Properties and Radiative Impact of the Extreme Smoke Event in the European Arctic in Spring 2006

In spring 2006 a special meteorological situation occurred in the European Arctic region giving record high levels of air pollution. The synoptic situation resulted in extensive transport of pollution predominantly from agricultural fires in Eastern Europe into the Arctic region and record high air-pollution levels were measured at the Zeppelin observatory at Ni-Alesun(78deg 54'N, 11deg 53'E) in the period from 25 April to 12 May. In the present study we investigate the optical properties of the aerosols from this extreme event and we estimate the radiative forcing of this episode. We examine the aerosol optical properties from the source region and into the European Arctic and explore the evolution of the episode and the changes in the optical properties. A number of sites in Eastern Europe, Northern Scandinavia and Svalbard are included in the study. In addition to AOD measurements, we explored lidar measurements from Minsk, ALOMAR (Arctic Lidar Observatory for Middle Atmosphere Research at Andenes) and Ny-Alesund. For the AERONET sites included (Minsk, Toravere, Hornsund) we have further studied the evolution of the aerosol size. Importantly, at Svalbard it is consistency between the AERONET measurements and calculations of single scattering albedo based on aerosol chemical composition. We have found strong agreement between the satellite dally MODIS AOD and the ground-based AOD observations. This agreement is crucial for the radiative forcing calculations. We calculate a strong negative radiative forcing for the most polluted days employing the analysed ground based data, MODIS AOD and a multi-stream model for radiative transfer of solar radiation.

Lund Myhre, C.↗
NASA NTRS1972

Corotation of an intermittent solar wind source

The measured electron content of the solar wind in mid-1970 exhibited a region of relatively high electron density that reappeared at intervals of about 27.8 days. It is shown that the repeating event cannot be reconciled with the concept of a long-enduring steady flow, even though the recurrence period is close to the rotation period of the sun. This evidence of transients is inferred from the short duration of each appearance of the interval of higher density; each should last for roughly one corotation interval if it is caused by a steady stream. The radio path was approximately 0.8 AU long, and the corotation interval exceeded 3 days. Other aspects of the content data patterns support the view that such transient events are common in the solar wind. The mid-1970 repeating event is an unusually good example of the intermittent character of flow regions in the solar wind that fluctuate on a time scale of days but endure as identifiable regions for many months. A sputtering corotating source of thin solar plasma streams could explain this series of events; it could also be explained in terms of a stream that is steady in density and speed but undulating north-south so that it passes into and out of the 0.8 AU radio path in a matter of a day or less.

Croft, T. A.↗
NASA NTRS1995

The solar origins of two high-latitude interplanetary disturbances

Two extremely similar interplanetary forward/reverse shock events, with bidirectional electron streaming were detected by Ulysses in 1994. Ground-based and Yohkoh/SXT observations show two strikingly different solar events that could be associated with them: an LDE flare on 20 Feb. 1994, and a extremely large-scale eruptive event on 14 April 1994. Both events resulted in geomagnetic storms and presumably were associated with coronal mass ejections. The sharply contrasting nature of these solar events argues against an energetic causal relationship between them and the bidirectional streaming events observed by Ulysses during its S polar passage. We suggest instead that for each pair of events. a common solar trigger may have caused independent instabilities leading to the solar and interplanetary phenomena.

Hudson, H. S.↗
NASA NTRS1975

Multispacecraft study of the solar wind velocity at interplanetary sector boundaries

The sector structure of the interplanetary magnetic field and the solar wind velocity at the sector boundaries are compared at separations of up to 0.3 AU, 50 deg in heliocentric longitude, and 7 deg in heliographic latitude, using data from Mariner 5 en route to Venus and from the near-earth Explorer 33, 34, and 35 satellites. The polarity pattern of the magnetic sectors is found to be very similar at the two locations, and 18 pairs of corresponding sector boundaries are identified. One-hour averages of solar wind velocities near the boundaries show that the velocities near earth exceed those measured by Mariner 5 by as much as 30%. Two possible explanations of the observed velocity differences are discussed: a preferential acceleration of sector boundaries with distance, possibly caused by stream-stream interactions; and a dependence of the solar wind velocity on heliographic latitude.

Rhodes, E. J., Jr.↗
NASA NTRS1983

Iron charge states observed in the solar wind

Solar wind measurements from the ULECA sensor of the Max-Planck-Institut/University of Maryland experiment on ISEE-3 are reported. The low energy section of approx the ULECA sensor selects particles by their energy per charge (over the range 3.6 keV/Q to 30 keV/Q) and simultaneously measures their total energy with two low-noise solid state detectors. Solar wind Fe charge state measurements from three time periods of high speed solar wind occurring during a post-shock flow and a coronal hole-associated high speed stream are presented. Analysis of the post-shock flow solar wind indicates the charge state distributions for Fe were peaked at approx +16, indicative of an unusually high coronal temperature (3,000,000 K). In contrast, the Fe charge state distribution observed in a coronal hole-associated high speed stream peaks at approx -9, indicating a much lower coronal temperature (1,400,000 K). This constitutes the first reported measurements of iron charge states in a coronal hole-associated high speed stream.

Ipavich, F. M.↗
NASA NTRS1994

Stream interfaces and energetic ions closer than expected: Analyses of Pioneers 10 and 11 observations

An empirical study of corotating interaction regions (CIRs) observed between 3.9 AU and 5.9 AU on Pioneers 10 and 11 shows that the main corotation energetic ion population (CEIP), which is associated with the trailing reverse shock, terminates within the CIR at a definite, structural boundary, which we show here is the stream interface. This new result has significant implications for solar wind and energetic particle modeling. In particular it implies either that the reverse shock forms closer to the stream interface than models suggest or that the theories that treat the generation and transport of these energetic ions, such as preshock Fermi acceleration and cross-field diffusion must be combined or extended. We test these scenarios by comparing the CEIP intensity profiles on the two sides of the stream interface. We find that while each automatically accounts for one or two aspects of the results none of them alone can account for all of our empirical results.

Intriligator, Devrie S.↗
DOE OSTI2023

InSPIRE 2.0 (Final Technical Report)

Co-locating solar projects and agriculture can provide mutual benefits to local farmers (e.g., dual revenue streams, increased yields from pollinator services, irrigation reductions) and to the solar projects (e.g., reduced timeline/costs for installation and O&M, expanded market, increased PV efficiency from a cooler, vegetated microclimate). While prior work sought to demonstrate the feasibility of agricultural co-location (or "agrivoltaic") opportunities, there is a fundamental gap in data available to developers, landowners, and state agencies that prevents widespread deployment of these mutually beneficial practices. This project addressed this gap by (1) establishing a stakeholder research working group composed of multi-sector industry leaders and academics to provide guidance and assist with outreach; (2) undertaking targeted field-based research projects evaluating solar and agriculture co-location tradeoffs; (3) conducting analysis and modeling studies that complement the field-based research; and (4) developing a data portal to consolidate all data on this topic in one location.

14 SOLAR ENERGY↗