Search NASA⌕ Search

SEARCH · Search NASA

Results for “SOLAR EFFECT”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Effect of solar radiation on a swarm of meteoric particles

The theory of the Poynting-Robertson effect is used to study the motion of meteors relative to a parent comet describing an undisturbed elliptical orbit. It is shown that any emitted particle proceeds to move retrogressively away from the comet to a certain maximum angular distance (as seen from the sun) depending on its sigma-s value, and then undergoes relative motion in the opposite forward direction. The time taken to reach this greatest elongation behind the comet is the same for all particles, and after twice this time the particles will have returned to zero angular displacement relative to the comet. For comet Encke the time for the elongation to return to zero is about 6600 y; for Halley it is about 200,000 y; for Temple-Tuttle (1965 IV) it is just over 100,000 y.

Lyttleton, R. A.↗
NASA NTRS1987

Solar wind effects on the outer ion coma of Comet Halley

A simple two-dimensional model is developed to examine the composition of the cometary ion coma in the region outside the ionopause which is strongly affected by the solar wind. Two-dimensional ion distributions are obtained assuming a cylindrically symmetric ion coma which accounts for the dynamic effects of the mass-loaded solar wind flow around the cometary ionosphere. The results of this model are discussed in the context of analyzing the GIOTTO ion data.

Flammer, K. R.↗
NASA NTRS1989

Line mixing effects in solar occultation spectra of the lower stratosphere - Measurements and comparisons with calculations for the 1932/cm CO2 Q branch

Line mixing effects have been observed in a CO2 Q branch recorded in 0.01/cm-resolution IR solar occultation spectra of the lower stratosphere. The spectral data were obtained by the Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer during the Spacelab 3 mission in the spring of 1985. Analysis of the 1932.47/cm Q branch of (C-12)(O-16)2 shows absorption coefficients below the band origin about 0.62 times those calculated using a standard Voigt line-shape function. Calculations of line mixing using the Lorentz halfwidths of the lines and a simple energy-gap scaling law to parameterize rotational energy transfer reproduce the observed absorption coefficients to about 10 percent. The present results provide the first quantitative information on air-broadened line mixing effects in a Q branch at low temperatures (about 210 K) and show that these effects are significant even at the low pressures of the lower stratosphere (about 100 mbar).

Rinsland, Curtis P.↗
NASA NTRS1980

A model of comet comae. II - Effects of solar photodissociative ionization

Improvements to a computer model of coma photochemistry are described. These include an expansion of the chemical reactions network and new rate constants that have been measured only recently. Photolytic reactions of additional molecules are incorporated, and photolytic branching ratios are treated in far greater detail than previously. A total of 25 photodissociative ionization (PDI) reactions are now considered (as compared to only 3 PDI reactions previously). Solar PDI of the mother molecule CO2 is shown to compete effectively with photoionization of CO in the production of observed CO(+). The CO(+) density peak predicted by the improved model, for CO2 or CO mother molecules, is deep in the inner coma, in better agreement with observation than the old CO2 model. However, neither CO2 nor CO mother molecule calculations reproduce the CO(+)/H2O(+) ratio observed in comet Kohoutek. PDI products of CO2, CO, CH4, and NH3 mother molecules fuel a complex chemistry scheme, producing inner coma abundances of CN, C2, and C3 much greater than previously calculated.

Huebner, W. F.↗
NASA NTRS1994

Combined Contamination and Space Environmental Effects on Solar Cells and Thermal Control Surfaces

For spacecraft in low Earth orbit (LEO), contamination can occur from thruster fuel, sputter contamination products and from products of silicone degradation. This paper describes laboratory testing in which solar cell materials and thermal control surfaces were exposed to simulated spacecraft environmental effects including contamination, atomic oxygen, ultraviolet radiation and thermal cycling. The objective of these experiments was to determine how the interaction of the natural LEO environmental effects with contaminated spacecraft surfaces impacts the performance of these materials. Optical properties of samples were measured and solar cell performance data was obtained. In general, exposure to contamination by thruster fuel resulted in degradation of solar absorptance for fused silica and various thermal control surfaces and degradation of solar cell performance. Fused silica samples which were subsequently exposed to an atomic oxygen/vacuum ultraviolet radiation environment showed reversal of this degradation. These results imply that solar cells and thermal control surfaces which are susceptible to thruster fuel contamination and which also receive atomic oxygen exposure may not undergo significant performance degradation. Materials which were exposed to only vacuum ultraviolet radiation subsequent to contamination showed slight additional degradation in solar absorptance.

Dever, Joyce A.↗
NASA NTRS1991

Solar zenith angle effects on vegetation indices in tallgrass prairie

The examination of the effects of solar zenith angle is based on computations of spectral vegetation indices (VIs) computed from spectral reflectance factors. The indices are examined in terms of biomass and LAI, and low-density canopies show no change in the low VI values during the day. The spectral VIs appear to measure the instantaneous, projected, and illuminated LAI canopy fraction relative to the illuminated substrate.

Middleton, Elizabeth M.↗
NASA NTRS1994

Observations of interplanetary Lyman-alpha with the Galileo Ultraviolet Spectrometer: Multiple scattering effects at solar maximum

The Galileo Ultravilet Spectrometer Experiment (UVS) obtained a partial celestial sphere map of interplanetary Lyman-alpha (IP L alpha) on 13-14 December 1990 during the first Earth encounter. The Galileo spacecraft was near the downwind axis of the local interstellar medium flow. These UVS measurements sampled the downwind, anti-sunward hemisphere. The data were modeled using a hot model of the interplanetary hydrogen density distribution with the goal of studying multiple scattering effects in the inner solar system. The derived ratio in the downwind direction of the observed brightness and a single scattering model brightness, both normalized to unity in the upwind direction, is 1.82 +/- 0.2. This brightness ratio requires a multiple scattering correction which is 36% larger than can be accounted for by theoretical calculations. The hot model may require: (1) a temperature perturbation of the interstellar wind velocity distribution or (2) an additional downstream source of interplanetary hydrogen. However, a more likely exlanation which affects the hot model is the latitude dependence of the radiation pressure. This dependence, based on the known solar L alpha flux latitude variation at solar maximum, causes a downwind brightness enhancement by preferential focusing of H-atoms with trajectory planes containing the solar poles. This result implies that radiation pressure near the solar poles is nearly independent of solar cycle and is insufficient to lead to a net repulsion of hydrogen atoms by the sun, as can occur near the ecliptic plane during the solar maximum. In addition, the UVS performed 13 observations of IP L alpha while in cruise between Venus and the Earth in 3 directions fixed in ecliptic coordinates.

Ajello, J. M.↗
NASA NTRS1982

Silicon materials task of the Low Cost Solar Array Project: Effect of impurities and processing on silicon solar cells

The effects of impurities and processing on the characteristics of silicon and terrestrial silicon solar cells were defined in order to develop cost benefit relationships for the use of cheaper, less pure solar grades of silicon. The amount of concentrations of commonly encountered impurities that can be tolerated in typical p or n base solar cells was established, then a preliminary analytical model from which the cell performance could be projected depending on the kinds and amounts of contaminants in the silicon base material was developed. The impurity data base was expanded to include construction materials, and the impurity performace model was refined to account for additional effects such as base resistivity, grain boundary interactions, thermal processing, synergic behavior, and nonuniform impurity distributions. A preliminary assessment of long term (aging) behavior of impurities was also undertaken.

Hopkins, R. H.↗
NASA NTRS1975

Numerical experiments on short-term meteorological effects on solar variability

A set of numerical experiments was conducted to test the short-range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day sets of integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Any causal relationships between solar variability and weather, for time scales of two weeks or less, rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model.

Somerville, R. C. J.↗
NASA NTRS1974

Numerical experiments on short-term meteorological effects of solar variability

Set of numerical experiments has been carried out to test the short range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Thus any causal relationships between solar variability and weather, for time scales of two weeks or less, will have to rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model.

Somerville, R. C. J.↗
NASA NTRS1978

Lunar interaction with the solar wind - Effects on lunar electrical conductivity estimates

The lunar electromagnetic response, measured at very low frequencies with the moon in the solar wind, is used to evaluate interior electrical conductivity at great depth and to determine limits on the size of possible lunar core. A theory is developed wherein compression of the magnetic field in the lunar tail cavity caused by inflowing plasma at the lunar limbs and in the lunar wake, bends the magnetic field in the lunar interior and thereby alters the tangential component of magnetic field observed on the dayside surface. This theory strongly indicates that cavity fringing cannot explain the enhanced East-West fluctuations. It is proposed that the East-West fluctuations might be due to diamagnetic currents caused by lunar surface photoelectrons in the lunar terminator region.

Goldstein, B. E.↗
NASA NTRS2002

RHESSI Investigations of the Neupert Effect in Solar Flares

In many solar flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission. This is known as the Neupert Effect and is believed to result when the same accelerated electrons that produce the bremsstrahlung hard X-rays also heat the plasma that produces the thermal bremsstrahlung soft X-rays. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating this effect since is covers the soft (down to 3 keV) and hard X-ray energy ranges with keV energy resolution, arcsecond-class angular resolution, and sub-second time resolution. Several GOES M-class flares have already been detected that show this general effect, but the detailed time histories suggest that there must be other heating mechanisms besides the thermalization of accelerated electrons that are heating the soft X-ray emitting plasma, even during the impulsive phase. Spatially-resolved hard and soft X-ray observations of these flares are also being investigated to determine what fraction of the heating is produced by the accelerated electrons.

Dennis, Brian R.↗
NASA NTRS2012

The Effects of Solar Variability on Earth's Climate: A Workshop Report

Solar irradiance, the flux of the Sun s output directed toward Earth, is Earth s main energy source.1 The Sun itself varies on several timescales over billions of years its luminosity increases as it evolves on the main sequence toward becoming a red giant; about every 11 years its sunspot activity cycles; and within just minutes flares can erupt and release massive amounts of energy. Most of the fluctuations from tens to thousands of years are associated with changes in the solar magnetic field. The focus of the National Research Council's September 2011 workshop on solar variability and Earth's climate, and of this summary report, is mainly magnetically driven variability and its possible connection with Earth's climate variations in the past 10,000 years. Even small variations in the amount or distribution of energy received at Earth can have a major influence on Earth's climate when they persist for decades. However, no satellite measurements have indicated that solar output and variability have contributed in a significant way to the increase in global mean temperature in the last 50 years. Locally, however, correlations between solar activity and variations in average weather may stand out beyond the global trend; such has been argued to be the case for the El Nino-Southern Oscillation, even in the present day. A key area of inquiry deals with establishing a unified record of the solar output and solar-modified particles that extends from the present to the prescientific past. The workshop focused attention on the need for a better understanding of the links between indices of solar activity such as cosmogenic isotopes and solar irradiance. A number of presentations focused on the timescale of the solar cycle and of the satellite record, and on the problem of extending this record back in time. Highlights included a report of progress on pyroheliometer calibration, leading to greater confidence in the time history and future stability of total solar irradiance (TSI), and surprising results on changes in spectral irradiance over the last solar cycle, which elicited spirited discussion. New perspectives on connections between features of the quiet and active areas of the photosphere and variations in TSI were also presented, emphasizing the importance of developing better understanding in order to extrapolate back in time using activity indices. Workshop participants reviews highlighted difficulties as well as causes for optimism in current understanding of the cosmogenic isotope record and the use of observed variability in Sun-like stars in reconstructing variations in TSI occurring on lower frequencies than the sunspot cycle. The workshop succeeded in bringing together informed, focused presentations on major drivers of the Sun-climate connection. The importance of the solar cycle as a unique quasi-periodic probe of climate responses on a timescale between the seasonal and Milankovitch cycles was recognized in several presentations. The signal need only be detectable, not dominant, for it to play this role of a useful probe. Some workshop participants also found encouraging progress in the top-down perspective, according to which solar variability affects surface climate by first perturbing the stratosphere, which then forces the troposphere and surface. This work is now informing and being informed by research on tropospheric responses to the Antarctic ozone hole and volcanic aerosols. In contrast to the top-down perspective is the bottom-up view that the interaction of solar energy with the ocean and surface leads to changes in dynamics and temperature. During the discussion of how dynamical air-sea coupling in the tropical Pacific and solar variability interact from a bottom-up perspective, several participants remarked on the wealth of open research questions in the dynamics of the climatic response to TSI and spectral variability. The discussion of the paleoclimate record emphasized that the link between solar varbility and Earth s climate is multifaceted and that some components are understood better than others. According to two presenters on paleoclimate, there is a need to study the idiosyncrasies of each key proxy record. Yet they also emphasized that there may be an emerging pattern of paleoclimate change coincident with periods of solar activity and inactivity, but only on long timescales of multiple decades to millennia. Several speakers discussed the effects of particle events and cosmic-ray variability. These are all areas of exciting fundamental research; however, they have not yet led to conclusive evidence for significant related climate effects. The key problem of attribution of climate variability on the timescales of the Little Ice Age and the Maunder Minimum were directly addressed in several presentations. Several workshop participants remarked that the combination of solar, paleoclimatic, and climate modeling research has the potential to dramatically improve the credibility of these attribution studies.

Source record↗
NASA NTRS2013

The Solar Poynting-Robertson Effect On Particles Orbiting Solar System Bodies: Circular Orbits

The Poynting-Robertson effect from sunlight impinging directly on a particle which orbits a Solar System body (planet, asteroid, comet) is considered from the Sun's rest frame. There appear to be no significant first-order terms in V(sub b)/c for circular orbits, where V(sub b) is the body's speed in its orbit about the Sun and c is the speed of light, when the particle's orbital semimajor axis is much smaller than the body's orbital semimajor axis about the Sun as is mainly the case in the Solar System.

circular orbits↗
NASA NTRS1994

An investigation of solar wind effects on the evolution of the Martian atmosphere

This investigation concentrated on the question of how atmosphere escape, related to both photochemistry and the Mars solar wind interaction, may have affected the evolution of Mars' atmosphere over time. The principal investigator and postdoctoral researcher adopted the premise that contemporary escape processes have dominated the losses to space over the past 3.5 billion years, but that the associated loss rates have been modified by solar evolution. A model was constructed for the contemporary escape scenario based on knowledge gained from both Venus in-situ measurements from Pioneer Venus Orbiter and Mars measurements from Phobos-2. Venus provided a valuable second example of a weakly magnetized planet having a similar solar wind interaction where we have more knowledge from observations. The model included photochemical losses from recombining ionospheric molecular ions, scavenging Martian upper atmosphere ('pickup') ions by the solar wind, and sputtering of the atmosphere by reentering pickup ions. The existence of the latter mechanism was realized during the course of the supported investigation, and is now thought by Jakosky and Pepin to explain some of the Martian noble gas isotope ratios.

Luhmann, Janet G.↗
NASA NTRS1994

The possibility of forming an inhomogeneous Sun and the solar neutrino effect

Recent observations confirm that the flux of neutrinos from the interior of the Sun is significantly less than what is expected on the basis of solar models. It has long been known that a low neutrino flux could result from a temperature in the Sun's core lower than the approximately 1.5 x 10(exp 7) K central temperature given by standard solar models. A low central temperature could occur if the solar interior were depleted in the so-called metals -- atomic species heavier than helium -- resulting in lower internal opacity. In this case, chemical abundances measured in the solar convection zone would be unrepresentative of the deep-interior abundances. The possibility of a compositionally inhomogeneous Sun has usually been discarded on the basis of cosmogonical arguments against the formation of such nonhomogeneity. This paper suggests that compositional nonhomogeneity could have arisen through unremarkable physical processes during the formation of the Sun, and that a compositionally inhomogeneous Sun remains a viable possibility for investigation of the solar neutrino problem.

Levy, E. H.↗