Search NASA⌕ Search

SEARCH · Search NASA

Results for “Distributed Solar”

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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The photospheric magnetic flux budget

The ensemble of bipolar regions and the magnetic network both contain a substantial and strongly variable part of the photospheric magnetic flux at any phase in the solar cycle. The time-dependent distribution of the magnetic flux over and within these components reflects the action of the dynamo operating in the solar interior. We perform a quantitative comparison of the flux emerging in the ensemble of magnetic bipoles with the observed flux content of the solar photosphere. We discuss the photospheric flux budget in terms of flux appearance and disappearance, and argue that a nonlinear dependence exists between the flux present in the photosphere and the rate of flux appearance and disappearance. In this context, we discuss the problem of making quantitative statements about dynamos in cool stars other than the Sun.

Schrijver, C. J.↗
NASA NTRS2003

Science Rationale for Jupiter Entry Probe as Part of JIMO

A Jupiter atmospheric entry probe as part of JIMO is a cost effective way to address fundamental science questions identified in the National Research Council Solar System Exploration Decadal Survey (SSEDS): New Frontiers in the Solar System, An Integrated Ex- ploration Strategy. Compared to either the cost of an entirely separate Jupiter mission, or the cost of JIMO itself, inclusion of such a probe on JIMO would be cost advantageous. The probe itself could be relatively simple, and could build on the Galileo Probe heritage. The SSEDS specifically identified the distribution of water across the Solar System as a Key Scientific Question. Correspondingly, knowing the water abun dance on Jupiter is fundamental to understanding almost every aspect of the evolution of the early solar nebula. The Galileo Probe obtained the abundance of several key elements in Jupiter's atmosphere, which data have already caused major rethinking of theories of how Jupiter formed and how the early solar nebula evolved. However, because of a combination of circumstances, the global abundance of the key element oxygen, in the form of water, was not obtained. Without knowledge of the jovian water abundance, further progress in understanding Solar System evolution and planet formation will be greatly inhibited. Therefore, quantifying jovian water abundance should be a goal of the very next mission to the jovian system. Such a measurement would be impossible via remote sensing from the JIMO orbiter because of the large distances the JIMO orbiter maintains from Jupiter. A Jupiter atmospheric entry probe as part of JIMO could achieve the fundamental water measurement. In order that a probe avoid repeating the Galileo probe's experience of failing to obtain the jovian water abundance, the probe should go deep, to at least 100 bars pressure. Probes to 100 bars have been accomplished many times in descending to the surface of Venus, and at 100 bars the temperature of the jovian atmosphere is 60-70 K less than the surface temperature of Venus.

Young, R. E.↗
NASA NTRS2017

The Mars Crustal Magnetic Field Control of Plasma Boundary Locations and Atmospheric Loss: MHD Prediction and Comparison with MAVEN

We present results from a global Mars time-dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3-D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic changes with time. We develop a physics-based, empirical algorithm to effectively summarize the multidimensional crustal field distribution. It is found that by organizing the model results using this new approach, the Mars crustal field shows a clear, significant influence on both the IMB and the BS. Specifically, quantitative relationships have been established between the field distribution and the mean boundary distances and the cross-section areas in the terminator plane for both of the boundaries. The model-predicted relationships are further verified by the observations from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our analysis shows that the boundaries are collectively affected by the global crustal field distribution, which, however, cannot be simply parameterized by a local parameter like the widely used subsolar longitude. Our calculations show that the variability of the intrinsic crustal field distribution in Mars-centered Solar Orbital itself may account for approx.60% of the variation in total atmospheric loss, when external drivers are static. It is found that the crustal field has not only a shielding effect for atmospheric loss but also an escape-fostering effect by positively affecting the transterminator ion flow cross-section area.

Global↗
NASA NTRS1997

Magnetic flux in modeled magnetic clouds at 1 AU and some specific comparisons to associated photospheric flux

In order to better understand the solar origins of magnetic clouds, statistical distributions of the estimated axial magnetic flux of 30 magnetic clouds at 1 AU, separated according to their occurrence during the solar cycle, were obtained and a comparison was made of the magnetic flux of a magnetic cloud to the aggregate flux of apparently associated photospheric magnetic flux tubes, for some specific cases. The 30 magnetic clouds comprise 12 cases from WIND, and the remainder from IMP-8, earlier IMPs, the International Sun-Earth Explorer (ISEE) 3 and HELIOS. The total magnetic flux along the cloud axis was estimated using a constant alpha, cylindrical, force-free flux rope model to determine cloud diameter and axial magentic field strength. The distribution of magentic fluxes for the 30 clouds is shown to be in the form of a skewed Gaussian.

Lepping, R. P.↗
NASA NTRS1978

A close-up of the sun

NASA's long-range plan for the study of solar-terrestrial relations includes a Solar Probe Mission in which a spacecraft is put into an eccentric orbit with perihelion near 4 solar radii (0.02 AU). The scientific experiments which might be done with such a mission are discussed. Topics include the distribution of mass within the Sun, solar angular momentum, the fine structure of the solar surface and corona, the acceleration of the solar wind and energetic particles, and the evolution of interplanetary dust. The mission could also contribute to high-accuracy tests of general relativity and the search for cosmic gravitational radiation.

Neugebauer, M.↗
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

Atlas of albedo and absorbed solar radiation derived from Nimbus 6 earth radiation budget data set, July 1975 to May 1978

An atlas of monthly mean global contour maps of albedo and absorbed solar radiation is presented. The atlas is based on 35 months of continuous measurements from July 1975 through May 1978. The data were retrieved from measurements made by the shortwave wide field-of-view radiometer of the first Earth Radiation Budget (ERB) instrument, which flew on the Nimbus 6 spacecraft in 1975. Profiles of zonal mean albedos and absorbed solar radiation are tabulated. These geographical distributions are provided as a resource for studying the radiation budget of the earth. This atlas of albedo and absorbed solar radiation complements the atlases of outgoing longwave radiation by Bess and Smith in NASA-RP-1185 and RP-1186, also based on the Nimbus 6 and 7 ERB data.

Smith, G. Louis↗
NASA NTRS1991

The sun's luminosity over a complete solar cycle

The Active Cavity Radiometer Irradiance Monitor (ACRIM I) measured the sun's luminosity from early 1980 to late 1989. The first account of the complete ACRIM I data set is presented and evidence is given which confirms that solar luminosity varies with the 11-yr solar cycle. This slow variation closely follows statistical measures of the distribution of magnetic and photospheric features on the solar surface. An exception to this correlation occurred in the form of a remarkable irradiance excess during 1980, at about the time of the sunspot maximum of solar cycle 21. The linkage, over a whole cycle, of luminosity variation to photospheric activity suggests the existence of an unknown physical mechanism other than the thermal diffusion model that explains luminosity deficits due to sunspots. Luminosity models connecting total irradiance to global indicators of solar activity are consistent with the gross features of the variability but fail to account for the 1980 irradiance excess.

Willson, Richard C.↗
NASA NTRS2020

SNPP and N20 VIIRS Solar Vector Orientation Knowledge Error Detected by SDSM Sun Views

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a passive scanning Earth observing satellite radiometer. The VIIRS has 22 spectral bands with design center wavelengths from 0.41 to 12.01 μm, providing data to generate more than 20 Earth’s biogeophysical parameters. Fourteen of the 22 VIIRS bands are the reflective solar bands (RSBs), detecting Earth reflected sunlight. To ensure data quality, regular on-orbit radiometric calibrations of the RSBs are performed, mainly through observations of an onboard solar diffuser (SD). The spectral radiance provided by the sunlit SD depends on the SD screen transmittance which is a function of the solar vector orientation. Additionally, on orbit the SD’s bidirectional reflectance distribution function (BRDF) changes its value due to solar bombardment. The BRDF change is derived from the SD stability monitor (SDSM) measurements. The SDSM views the Sun through a screen with through holes (the SDSM screen) and the SD at almost the same time. The time series of the ratio of the signal strengths is a measure of the SD BRDF on-orbit change. Hence the measurements of the on-orbit SD BRDF change depends on the SDSM screen relative transmittance which is also solar vector orientation dependent. In this paper for both the SNPP and the NOAA-20 VIIRS instruments we examine the solar vector orientation knowledge error through matching the SDSM screen relative effective transmittances derived from the calibration data collected on the yaw maneuver and the regular orbits.

SNPP↗
NASA NTRS1981

Solar cycle signal in air temperature in North America - Amplitude, gradient, phase and distribution

The considered investigation was motivated by three factors. One is related to an extension of single-channel MESA to multi-channel by Strand (1977), Morf et al. (1978), and Jones (1978). MESA is a high-resolution signal processing and spectrum analysis technique due to Burg (1975). The considered developments resulted in the discovery of the 11-year solar cycle signal in the change of the length of day by Currie (1980, 1981). They also led Currie (1981) to study the phase spectrum of the 11-year term in height H of sea level. The investigation tries to clarify the phase relations among the involved parameters. The second factor is connected with an application of the linear time domain technique used by Currie (1981) to temperature records to obtain more accurate information regarding the signal amplitude. The third factor of motivation is related to increases in the number of stations available for an analysis, the greater average length of the records, and the more accurate data set.

Currie, R. G.↗
NASA NTRS1984

High-frequency wave normals in the solar wind

High-frequency (0.01-0.04 Hz) magnetic fluctuations in 506 ten-minute intervals of contemporaneous Explorer 35 and Apollo 12 measurements made in the solar wind near the morning side of the earth's bow shock show the presence of a large population of disturbances resembling Alfven waves. Each wavefront normal is systematically aligned (median deviation = 35 deg) with the associated ten-minute average of the magnetic field. Because of variability in the direction of this ten-minute average, from one interval to another, the coupled wavefront-normal distribution is nearly isotropic in solar ecliptic coordinates, in contrast with the results of other studies of waves at much lower frequency indicating outward propagation from the sun. Presumably the high frequency waves discussed here are stirred into isotropy (in solar ecliptic coordinates) by following the low frequency fluctuations. As these waves maintain their alignment of wavefront-normal with the field ten-minute average despite the great variation of the field ten-minute average, a strong physical alignment constraint is inferred.

Herbert, F.↗
NASA NTRS1995

Kinematic models of supergranular diffusion on the Sun

We develop kinematic models of diffusion generated by supergranulation at the solar surface. These models use current observations for the size, horizontal velocity, and lifetime of supergranules. Because there is no observational description of the appearance and disappearance of supergranules, we investigate models using several plausible evolution processes, including the effect of different lifetime distribution functions for the cells. The results are quite insensitive to the methods chosen to replace old supergranules, the distribution of cell lifetimes, and even the cell lifetime itself, for mean lifetimes between 15 to 30 hr. Calculated diffusion coefficients range between 500 and 700 sq km/s, in agreement with the best fit diffusion coefficients used by Sheeley and his collaborators to model the large-scale distribution of magnetic fields over the solar surface. However, our models do not explain the field distribution in plage, and they predict that virtually all the strong field in quiet Sun exists in relatively isolated clumps. We suggest possible mechanisms for the creation of plage and the bright network seen in quiet Sun.

Simon, G. W.↗
NASA NTRS1994

The kinetics and dynamics of the coma of Halley's comet

This grant to the University of Michigan supported the efforts of Michael R. Combi to serve as a co-investigator in collaboration with a larger effort by the principal investigator, William Smyth of Atmospheric and Environmental Research, Inc. The overall objective of this project was to analyze in a self-consistent manner unique optical O((sup 1)D) and NH2 ultra-high resolution line profile data of excellent quality and other supporting lower-resolution spectral data for the coma of comet P/Halley by using highly developed and physically-based cometary coma models in order to determine and explain in terms of physical processes the actual dynamics and photochemical kinetics that occur in the coma. The justification for this work is that it provides a valuable and underlying physical base from which to interpret significantly different types of coma observations in a self-consistent manner and hence bring into agreement (or avoid) apparent inconsistencies that arise from non-physically based interpretations. The level of effort for the Michigan component amounted to less than three person-months over a planned period of three years. The period had been extended at no extra cost to four years because the Michigan grant and the AER contract did not have coincident time periods. An effort of somewhat larger scope was undertaken by the PI. The importance of the O((sup 1)D) profiles is that they provide a direct trace of the water distribution in comets. The line profile shape is produced by the convolution of the outflow velocity and thermal dispersion of the parent water molecules with the photokinetic ejection of the oxygen atoms upon photodissociation of the parent water molecules. Our understanding of the NH2 and its precursor ammonia are important for comet-to-comet composition variations as they relate to the cosmo-chemistry of the early solar nebula. Modeling of the distribution of NH2 is necessary in order to infer the ammonia production rates from NH2 observations.

Combi, Michael R.↗
NASA NTRS1979

Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion

This letter reports the discovery of an unusual Allende inclusion that is rich in hibonite, Ca(Al, Ti, Mg)12O19, the most refractory and possibly the most primitive major oxide mineral from the solar nebula. The Mg and Ca isotopic compositions of this hibonite-rich inclusion are studied in order to investigate the distribution of Al-26 in the solar system and to extend the search for isotopic anomalies. The Mg results indicate that no Mg isotopic anomalies are present, that the initial Al-26/Al-27 ratio for the inclusion when it crystallized was less than 200 billionths, and that the Mg mass-fractionation effect in the inclusion must be less than about 20 per mil/amu for the hibonite and 10 per mil/amu for other phases. The Ca studies reveal that large Ca mass-fractionation effects of about 7.5 per mil/amu are present and that additional small 'nonlinear' effects of presumably nuclear origin at a level of about 1 to 2 per mil are present in at least Ca-42. A plausible model for the evolution of the hibonite-rich inclusion is outlined.

Lee, T.↗
NASA NTRS1989

Distribution function of continuously created newborn and pickup ions in outer cometary exospheres

The time evolution of the distribution function of newborn ions in the solar wind is investigated using a quasi-linear-type diffusion equation. The initial distribution is taken to be a ring beam, which is approximated by delta function in pitch angle and velocity, and it is assumed that the ions are created at a constant rate with a similar distribution. A long-time asymptotic form of ion distribution is obtained, which is a mixture of newborn ions and ions generated throughout the entire process. It is shown that the time asymptotic distribution function exists even in the presence of a continuous ionization process. The stability of the long-time asymptotic distribution was examined for the case of parallel propagation, and the results show that the distribution function can be unstable to low-frequency hydromagnetic waves. The results of the analysis were found to agree with recent satellite observations.

Gaffey, J. D., Jr.↗
NASA NTRS1990

Atlas of albedo and absorbed solar radiation derived from Nimbus 7 Earth radiation budget data set, November 1978 to October 1985

An atlas of monthly mean global contour maps of albedo and absorbed solar radiation is presented. This atlas contains 7 years of continuous data from November 1978 through October 1985. The data were retrieved from measurements made by the second Earth Radiation Budget (ERB) wide field-of-view instrument, which flew on the Nimbus 7 spacecraft in 1978. The deconvolution method used to produce these data is briefly discussed here so that the user may understand their generation and limitations. These geographical distributions of albedo and absorbed solar radiation are provided as a resource for researchers studying the radiation budget of the Earth. This atlas of albedo and absorbed solar radiation complements the atlases of outgoing longwave radiation by Bess and Smith, also based on the Nimbus 6 and 7 ERB data.

Smith, G. Louis↗
NASA NTRS1996

Ways that our Solar System helps us understand the formation of other planetary systems and ways that it doesn't

Models of planetary formation can be tested by comparison of their ability to predict features of our Solar System in a consistent way, and then extrapolated to other hypothetical planetary systems by different choice of parameters. When this is done, it is found that the resulting systems are insensitive to direct effects of the mass of the star, but do strongly depend on the properties of the disk, principally its surface density. Major uncertainty results from lack of an adequate theoretical model that predicts the existence, size, and distribution of analogs of our Solar System, particularly the gas giants Jupiter and Saturn. Nevertheless, reasons can be found for expecting that planetary systems, including those containing biologically habitable planets similar to Earth, may be abundant in the Galaxy and Universe.

NASA Discipline Exobiology↗