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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Solar Modulation of Low-Energy Antiproton and Proton Spectra Measured by BESS

The spectra of low-energy cosmic-ray protons and antiprotons have been measured by BESS in nine high-latitude balloon flights between 1993 and 2004. These measurements span a range of solar activity from the previous solar minimum through solar ma>:im%am and the onset of the present solar minimum, as well as a solar magnetic field reversal from positive to negative in 2000. Because protons and antiprotons differ only in charge sign, these simultaneous measurements provide a sensitive probe of charge dependent solar modulation. The antiproton to proton ratio measured by BESS is consistent with simple spherically symmetric models of solar modulation during the Sun's positive polarity phase, but favor charge-sign-dependent drift models during the negative phase. The BESS measurements will be presented and compared to various models of solar modulation.

Mitchell, John W.↗
NASA NTRS1976

Interaction of solar wind with Mercury and its magnetic field

A brief review is presented of magnetic field and solar wind electron observations by Mariner 10 spacecraft. The intrinsic magnetic field of the planet Mercury and the implications of such a field for the planetary interior are also discussed.

Ness, N. F.↗
NASA NTRS1972

Apollo 15 surface science summary.

The Apollo 15 mission was the fourth manned lunar landing and the northernmost location yet visited. The landing site on the southeastern edge of the Imbrium Basin afforded the opportunity of studying several unique lunar features, the Apennine Mountains, Hadley Rille, and the Imbrium Basin fill. Detailed geological study of the data returned from the mission provided new insight into the structure and history of the Basin. A third Apollo Lunar Surface Experiment Package was deployed during the mission containing seven experiments: Passive Seismometer (PSE), Heat Flow (HFE), Surface Magnetometer (LSM), Suprathermal Ion Detector (SIDE), Cold Cathode Gauge (CCGE), Solar Wind Spectrometer (SWS), and a Dust Detector. We have been able to triangulate on the sources of moonquakes and to observe simultaneous nighttime and daytime changes in the moon's magnetic field, solar wind flux, and the neutral and ionized components of the moon's tenuous atmosphere.

Beattie, D. A.↗
NASA NTRS1985

Stellar activity cycles

The variety of stellar chromospheric and coronal activity provides a framework for understanding solar and stellar magnetic activity. It is pointed out that the recognition of an 11-yr periodicity within the record of sunspot numbers is a relatively recent discovery of just over a century ago. The solar activity cycle is examined, taking into account the sunspot cycle, and solar dynamo models. Time-averaged stellar chromospheric activity levels are considered along with long-term activity fluctuations of cool stars. Attention is given to the direct measurement of stellar magnetic fields, solar luminosity variations, the RS Canum Venaticorum and BY Draconis variables, continuum variations in lower main sequence stars, chromospheric variations in lower main sequence stars, and chromospheric variations in evolved stars.

Baliunas, S. L.↗
NASA NTRS1982

The structure, energy balance, and winds of cool stars

Solar magnetic field phenomena which occur in cool stars are summarized. Factors which can produce magnetic fields in stars are listed. Information on cool star atmospheres, provided by high dispersion spectra, is discussed. These spectra show that in Beta Dra (G2 Ib) the transition lines are red shifted (an antiwind), perhaps indicating downflows in closed magnetic flux tubes, as seen in the solar flux tubes above sunspots. The G and K giants and supergiants are classed as active, quiet, or hybrid, depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominantly open geometry with a few closed flux tubes embedded.

Linsky, J. L.↗
NASA NTRS2010

Observations of the Magnetic Field and Plasma in the Heliosheath by Voyager 2 from 2007.7 to 2009.4

The density and temperature profiles of the plasma measured by Voyager 2 (V2) behind the termination shock changed abruptly near 2008.6 from relatively large average values and large fluctuations during 2007.7 to 2008.6 (interval A) to relatively low average values and very small-amplitude fluctuations during 2008.6 to 2009.4 (interval B). This paper shows that the change in the magnetic field strength B(t) was less abrupt than the plasma changes, and the fluctuations of the magnetic field strength in interval B were of moderate amplitude, with indications of a quasiperiodic structure in part of the interval. The magnetic field was directed away from the sun (positive polarity) approx. 78% +/- 5% of the time in both interval A and interval B, changing in an irregular way from positive to negative polarities throughout the interval. The polarity distribution indicates that the minimum latitudinal extent of the heliospheric current sheet (HCS) was near V2 throughout the interval, consistent with the extrapolated minimum latitudes of the HCS computed from solar magnetic field observations. Thus, V2 was observing magnetic fields from the southern polar coronal hole most of the time. The distribution of B was lognormal in interval A and Gaussian interval B.

Burlaga, L. F.↗
NASA NTRS2012

Multiscale Dynamics of Solar Magnetic Structures

Multiscale topological complexity of the solar magnetic field is among the primary factors controlling energy release in the corona, including associated processes in the photospheric and chromospheric boundaries.We present a new approach for analyzing multiscale behavior of the photospheric magnetic flux underlying these dynamics as depicted by a sequence of high-resolution solar magnetograms. The approach involves two basic processing steps: (1) identification of timing and location of magnetic flux origin and demise events (as defined by DeForest et al.) by tracking spatiotemporal evolution of unipolar and bipolar photospheric regions, and (2) analysis of collective behavior of the detected magnetic events using a generalized version of the Grassberger-Procaccia correlation integral algorithm. The scale-free nature of the developed algorithms makes it possible to characterize the dynamics of the photospheric network across a wide range of distances and relaxation times. Three types of photospheric conditions are considered to test the method: a quiet photosphere, a solar active region (NOAA 10365) in a quiescent non-flaring state, and the same active region during a period of M-class flares. The results obtained show (1) the presence of a topologically complex asymmetrically fragmented magnetic network in the quiet photosphere driven by meso- and supergranulation, (2) the formation of non-potential magnetic structures with complex polarity separation lines inside the active region, and (3) statistical signatures of canceling bipolar magnetic structures coinciding with flaring activity in the active region. Each of these effects can represent an unstable magnetic configuration acting as an energy source for coronal dissipation and heating.

Magnetic fields↗
NASA NTRS1976

Direction-finding measurements of type III radio bursts out of the ecliptic plane

A series of two-dimensional direction-finding measurements for three type III solar radio bursts is presented which is based on spin-modulation measurements from two satellites (IMP 8 and Hawkeye I) whose spin axes were nearly perpendicular to each other. The two-dimensional direction-finding technique is combined with a model of the solar-wind plasma density in order to provide determinations of type III source locations out of the ecliptic plane as well as information on the three-dimensional structure of the solar magnetic field at radial distances of 0.2 to 1.0 AU from the sun. The direction-finding technique is described in detail, characteristics of the bursts observed by the two satellites are summarized, and the solar-wind model is outlined. The results show that the source locations follow an Archimedean spiral when projected onto the ecliptic plane but usually follow a constant heliocentric latitude perpendicular to that plane. It is also found that measured source sizes are a factor of two larger than the angular sizes of previously reported solar-flare electron emissions, that the spin-modulation factor tends to be largest near the beginning of a type III event, and that the arrival direction of the radiation varies systematically during an event.

Baumback, M. M.↗
NASA NTRS1980

X-ray bright points and the solar cycle dependence of emerging magnetic flux

Soft X-ray imaging of the solar corona during the period 1970 to 1978 resulted in significant modifications to the view of the solar cycle with respect to both the properties of the large scale (coronal holes) and small scale (X-ray Bright Points) solar magnetic field. In the latter case, the particular contribution is to the emerging magnetic flux. Sounding rocket observations combined with the Skylab data indicate that the XBP are anticorrelated with sunspot number and are the dominant contributors to the solar cycle. A continuous data set covering a complete cycle would enable the validity of this result which has serious implications for the nature of the solar dynamo, to be confirmed.

Davis, J. M.↗
NASA NTRS1993

Continued Development of an Ultra-Narrow Bandpass Filter for Solar Research

The objective of work under this task was to develop ultranarrow optical bandpass filters and related technology necessary for construction of a compact solar telescope capable of operating unattended in space. The scientific problems to which such a telescope could be applied include solar seismology, solar activity monitoring, solar irradiance variations, solar magnetic field evolution, and the location of targets for narrow-field specialized telescopes. We have demonstrated a Y-cut lithium-niobate Fabry-Perot etalon. This filter will be used on the Flare Genesis Experiment. We also obtained solar images with a Z-cut etalon. The technical report on etalon filters is attached to this final report. We believe that work under this grant will lead to the commercial availability of a universal optical filter with approximately 0.1 A bandwidth. Progress was made toward making a suitable 1-2 A tunable blocker filter, but it now appears that the best approach is to make a double-cavity etalon that will not require such a narrow blocker. Broader band blockers are commercially available.

Rust, David M.↗
NASA NTRS1998

A Normal Incidence X-ray Telescope (NIXT) Sounding Rocket Payload

The solar corona, and the coronae of solar-type stars, consist of a low-density magnetized plasma at temperatures exceeding 10(exp 6) K. The primary coronal emission is therefore in the UV and soft X-ray range. The observed close connection between solar magnetic fields and the physical parameters of the corona implies a fundamental role for the magnetic field in coronal structuring and dynamics. Variability of the corona occurs on all temporal and spatial scales - at one extreme, as the result of plasma instabilities, and at the other extreme driven by the global magnetic flux emergence patterns of the solar cycle.

Golub, Leon↗
NASA NTRS1976

Coronal propagation: Variations with solar longitude and latitude

Observational results on the East-West effect are summarized and discussed in the context of existing models of coronal propagation. The variation of the number of events with solar longitude is shown to be surprisingly similar for particles covering a large interval of rigidities. Also, over large longitudinal distances, time delays to the event onset and maximum intensity are independent of energy and velocity. This has important implications and will require probably a transport process which is determined by fundamental properties of solar magnetic fields, e.g. reconnection processes between open and closed field configurations. The relative role of open and closed field configurations is extensively discussed. Some evidence is presented that the acceleration of protons to higher (approximately 10 MeV) energies is related with a shock wave traveling in the solar atmosphere. The importance of measurements performed from spacecraft out-of-the-ecliptic plane is stressed.

Wibberenz, G.↗
NASA NTRS1976

Hydraulic concentration of magnetic fields in the solar photosphere. III - Fields of one or two kilogauss

Detailed analysis of weak and strong lines suggests that the magnetic fields in isolated intense flux tubes in supergranule boundaries in the solar photosphere may be as large as 2000 gauss. This paper is a concise systematic review of hydrodynamic effects that might compress a magnetic field to great intensity. The properties of force-free fields are reviewed to show that they do not contribute to concentration of magnetic fields, in spite of the popular notion to the contrary. Of the seven effects considered, it is concluded that only cooling of the gas within the field can produce the high field densities inferred from observation. It is shown that inhibition of convection appears not to possess the necessary qualitative cooling features and that overstability, generating transverse hydromagnetic waves - essentially Alfven waves - is the only way to account for the cooling and field intensification.

Parker, E. N.↗
NASA NTRS1984

Large scale temporal and radial gradients in the IMF - Helios 1, 2, ISEE-3, and Pioneer 10, 11

Recent investigations using measurements at 1 AU have discovered three types of long term variation in the interplanetary magnetic field: solar minimum decreases, solar maximum enhancements, and small decreases around solar reversal. In this study the 1972-1982 Helios 1, 2, ISEE-3, and Pioneer 10, 11 observations between 0.3 and 12 AU are examined to further investigate these changes. It was found that all three IMF solar cycle effects are also present in the Helios and Pioneer measurements, confirming that these variations occur throughout the low latitude heliosphere. In addition, the comparison of measurements by identical magnetometers on ISEE-3, Pioneer 10 and Pioneer 11 has revealed a more rapid decrease in IMF intensity than predicted by classical Parker theory. Causes and ramifications of both the long term variations and steeper-than-expected radial gradients in the interplanetary magnetic field are discussed.

Slavin, J. A.↗
NASA NTRS1991

Compressible magnetic convection - Formulation and two-dimensional models

Details on a formulation and numerical solution of the equations of time-dependent magnetized convection are presented. Results on the transition between weak and strong magnetic fields where the highly nonlinear behavior commences are discussed, and the sensitivity of these results to the value of the magnetic resistivity, which can significantly influence the details of the interactions, is indicated. Consideration is given to the consequences of the findings for modeling stellar and solar magnetic fields.

Fox, Peter A.↗
NASA NTRS1995

Some remarks on waves in the solar wind

Waves are significant to the solar wind in two ways as modifiers of the particle distribution functions, and as diagnostics. In addition, the solar wind serves as an important laboratory for the study of plasma wave processes, as it is possible to make detailed measurements of phenomena which are too small to be easily measured by laboratory sized sensors. There are two areas where waves (we include discontinuities under this heading) must make important modifications of the distribution functions: in accelerating the alpha particles to higher speeds than the protons (Marsch et al.) and in accelerating the solar wind itself. A third area is possibly in maintaining the relative isotropy of the solar wind ion distribution in the solar wind rest frame. As the solar wind is nearly collisionless, the ions should conserve magnetic moment in rushing out from the sun, and therefore Tperp/B should be relatively constant, but it is obviously not. This has not received much attention. The waves, both electromagnetic and electrostatic, which are pan of the solar Type 111 burst phenomenon, have been extensively studied as examples of nonlinear plasma phenomena, and also used as remote sensors to trace the solar magnetic field. The observations made by Ulysses show that the field can be traced in this way out to perhaps a little more than an A.U., but then the electromagnetic pan of the type 111 burst fades out. Nevertheless, sometimes Langmuir waves appear at Ulysses at an appropriate extrapolated time. This seems to support the picture in which the electromagnetic waves at the fundamental plasma frequency are trapped in density fluctuations. Langmuir waves in the solar wind are usually in quasi-thermal equilibrium quasi because the solar wind itself is not isothermal. The Observatory of Paris group (Steinberg. Meyer-Vernet, Hoang) has exploited this with an experiment on WIND which is capable of providing density and temperature on a faster time scale than hitherto. Recently it has been found that Langmuir waves are associated with magnetic holes. This may help to elucidate the nature of magnetic holes. Nonlinear processes are important in the transformation of wave energy to panicle energy. Some recent examples from WIND data will be shown.

Kellogg, Paul J.↗