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Results for “SOLAR MAGNETIC FIELD”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Conversion of magnetic field energy into kinetic energy in the solar wind

The outflow of the solar magnetic field energy (the radial component of the Poynting vector) per steradian is inversely proportional to the solar wind velocity. It is a decreasing function of the heliocentric distance. When the magnetic field effect is included in the one-fluid model of the solar wind, the transformation of magnetic field energy into kinetic energy during the expansion process increases the solar wind velocity at 1 AU by 17 percent.

Whang, Y. C.↗
NASA NTRS1991

Generation and behavior of solar system magnetic fields

A range of problems aimed primarily at elucidating the character and consequences of magnetic-field generation in the solar system and at testing ideas against known properties of natural magnetic fields are covered. Among the specific subjects currently under investigation are the magnetohydrodynamic (MHD) character of the protosolar nebula, including the generation and behavior of magnetic fields, the electrical conductivity of dusty nebular gas, transient magnetodynamic and electrodynamic nebular phenomena, and the generation and dynamical behavior of planetary magnetic fields. During the past year, the focus of this research was on disk magnetic field generation and transient MHD heating events possibly associated with the protoplanetary nebula.

Levy, Eugene H.↗
NASA NTRS1991

The time evolution of magnetic fields on solar-like stars

Magnetic fields play a crucial role in governing the rotational evolution of solarlike stars. Techniques for measuring stellar magnetic fields are reviewed, and the most recent determinations of magnetic-field strengths and surface-area coverages on cool stars are analyzed for correlations with age. Tentative evidence for a decrease in magnetic flux with age is found, primarily caused by a reduction in the magnetic area filling factor with time.

Saar, Steven H.↗
NASA NTRS1979

The effect of magnetic fields on solar luminosity

The paper presents an investigation into the influence of magnetic fields in sunspots and faculae on solar luminosity, using measurements of the solar constant from ground level and from space. Attention is given to an analysis that shows that it is difficult to devise an atmospheric mechanism that would rapidly lower visible and infrared transmission in response to sunspots, increase it in response to faculae, and anticipate the magnetic development of these features by about one day. It is shown that the phase shift of the luminosity variation provides a promising new technique to determine the depth at which the magnetic fields of sunspots and faculae redistribute the flow of convective energy.

Foukal, P.↗
NASA NTRS1995

On the spatial distribution of magnetic fields on the solar surface

Recent measurements of solar surface magnetic fields suggest that the spatial distribution of these fields is fractal. In order to understand the physical basis for such geometric complexity, we study here the advection of magnetic flux tubes relatively simple random motions on the surface of a fluid and investigate the spatial statistics of the resulting surface field. While this study does not directly address the question of why solar surface fields have the observed spatial structure, it is designed to build our intuition about how surface flows lead to complex spatial structuring of magnetic fields. As part of our study, we discuss the various methods by which one can describe the spatial distribution of the surface magnetic flux and relate them mathematically; this turns out to be a crucial point of our work since, as we show, a number of previous analyses have misinterpreted the analysis procedures for determining fractal dimensions. Our principal result is the explicit demonstration that simple random flows lead to magnetic flux spatial distributions with a multifractal dimension spectrum. Furthermore, we demonstrate that this magnetic spatial structure is generic, i.e., is characteristic of a very large class of random flows.

Tao, L.↗
NASA NTRS1992

Magnetic diffusion and flare energy buildup

Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear 2D force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field and photospheric velocity field are used, it is found that 3-4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal magnetic energy, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.

Wu, S. T.↗
NASA NTRS1977

The mean magnetic field of the sun - Observations at Stanford

A solar telescope has been built to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph connected to a 22.9-m vertical Littrow spectrograph. Sun-as-a-star integrated-light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean-field magnitude has been about 0.15 G, with a typical measurement error of less than 0.05 G. The mean-field polarity pattern is essentially identical to the interplanetary-magnetic-field sector structure (seen near earth with a four-day lag). The differences in the observed structures can be understood in terms of a 'warped current sheet' model.

Scherrer, P. H.↗
NASA NTRS1977

The mean magnetic field of the sun: Observations at Stanford

A solar telescope was built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field were made daily since May 1975. The typical mean field magnitude is about 0.15 gauss with typical measurement error less than 0.05 gauss. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (seen near the earth with a 4 day lag). The differences in the observed structures can be understood in terms of a warped current sheet model.

Scherrer, P. H.↗
NASA NTRS2003

Beyond Solar-B: MTRAP, the Magnetic Transition Region Probe

The next generation of solar missions will reveal and measure fine-scale solar magnetic fields and their effects in the solar atmosphere at heights, small scales, sensitivities, and fields of view well beyond the reach of Solar-B. The necessity for, and potential of, such observations for understanding solar magnetic fields, their generation in and below the photosphere, and their control of the solar atmosphere and heliosphere, were the focus of a science definition workshop, 'High-Resolution Solar Magnetography from Space: Beyond Solar-B,' held in Huntsville Alabama in April 2001. Forty internationally prominent scientists active in solar research involving fine-scale solar magnetism participated in this Workshop and reached consensus that the key science objective to be pursued beyond Solar-B is a physical understanding of the fine-scale magnetic structure and activity in the magnetic transition region, defined as the region between the photosphere and corona where neither the plasma nor the magnetic field strongly dominates the other. The observational objective requires high cadence (less than 10s) vector magnetic field maps, and spatially resolved spectra from the IR, visible, vacuum UV, to the EUV at high resolution (less than 50km) over a large FOV (approximately 140,000 km). A polarimetric resolution of one part in ten thousand is required to measure transverse magnetic fields of less than 30G. The latest SEC Roadmap includes a mission identified as MTRAP to meet these requirements. Enabling technology development requirements include large, lightweight, reflecting optics, large format sensors (16K x 16K pixels) with high QE at 150 nm, and extendable spacecraft structures. The Science Organizing Committee of the Beyond Solar-B Workshop recommends that: (1) Science and Technology Definition Teams should be established in FY04 to finalize the science requirements and to define technology development efforts needed to ensure the practicality of MTRAP's observational goals; (2) The necessary technology development funding should be included in Code S budgets for FY06 and beyond to prepare MTRAP for a new start no later than the nominal end of the Solar-B mission, around 2010.

Davis, John M.↗
NASA NTRS1985

Diurnal variation of galactic cosmic ray intensity on quiet days

A detailed study of the diurnal variation on long term basis was performed on geomagnetically quiet days using the experimental data of the cosmic ray intensity from the worldwide neutron monitoring stations. During the period when the polarity of the solar magnetic field in the Northern Hemisphere of the sun is negative the phase and amplitude of the diurnal anisotropy on quiet days was observed to remain almost constant. When the polarity of solar magnetic field in the Northern Hemisphere changes from negative to positive, a shift in the phase of the diurnal anisotropy on quiet days towards earlier hours is observed and the shift is found to be maximum during minimum solar activity periods 1953-54 and 1975-76. When the polarity of solar magnetic field changes from positive to negative in the Northern Hemisphere of the Sun the phase of the diurnal anisotropy on quiet days recovers to its usual direction of corotational anisotropy and is observed to remain almost constant till the polarity of the solar magnetic field does not change.

Kumar, S.↗
NASA NTRS1981

Magnetic fields on the Sun

Synoptic observations of solar magnetic fields are discussed. Seen in long-term averages, the magnetic fields of the Sun show distinctive behavior. The active-region latitudes are characterized by magnetic fields of preceding polarity. The flow of following polarity fields to make up the polar fields is episodic, not continuous. This field motion is a directed poleward flow and is not due to diffusion. The total magnetic flux on the solar surface, which is related linearly to the calcium emission in integrated sunlight, varies from activity minimum to maximum by a factor of 2 or 3. Nearly all this flux is seen at active-region latitudes-only about 1% is at the poles. The total flux of the Sun disappears from the surface at a very rapid rate and is replaced by new flux. All the field and flux patterns that we see originate in active-region latitudes. The polar magnetic fields of the Sun were observed to change polarity recently. The variations of the full-disk solar flux are shown to lead to the proper rotation rate of the Sun, but the phase of the variations is constant for only a year or two at most.

Howard, R.↗
NASA NTRS1992

Electromechanical coupling of the solar atmosphere; Proceedings of the OSL Workshop, Capri, Italy, May 27-31, 1991

The present conference discusses the role of magnetic flux tubes as communication channels, flux tube sizes and their temporal evolution, magnetic field line topology in the solar active regions, weak solar magnetic fields, explosive events and magnetic reconnection in the solar atmosphere, and 3D kinematic reconnection of plasmoids with nulls. Also discussed are coronal heating mechanisms, coronal heating through a lack of MHD equilibrium, Alfven waves in current-carrying inhomogeneous plasmas, hydrostatic models of X-ray coronal loops, MHD turbulence in an expanding atmosphere, and hot mass transport in the solar active prominence.

Spicer, Daniel S.↗
NASA NTRS1972

Large-scale properties of the interplanetary magnetic field

Early theoretical work of Parker is presented along with the observational evidence supporting his Archimedes spiral model. Variations present in the interplanetary magnetic field from the spiral angle are related to structures in the solar wind. The causes of these structures are found to be either nonuniform radial solar wind flow or the time evolution of the photospheric field. Coronal magnetic models are related to the connection between the solar magnetic field and the interplanetary magnetic field. Direct extension of the solar field-magnetic nozzle controversy is discussed along with the coronal magnetic models. Effects of active regions on the interplanetary magnetic field is discussed with particular reference to the evolution of interplanetary sectors. Interplanetary magnetic field magnitude variations are shown throughout the solar cycle. The percentage of time the field magnitude is greater than 10 gamma is shown to closely parallel sunspot number. The sun's polar field influence on the interplanetary field and alternative views of the magnetic field structure out of the ecliptic plane are presented. In addition, a variety of significantly different interplanetary field structures are discussed.

Schatten, K. H.↗
NASA NTRS1986

The interplanetary magnetic field during solar cycle 21 ISEE-3/ICE observations

Temporal variations in the IMF during solar cycle 21 are investigated using magnetic field observations collected by the vector helium magnetometer on the ISEE-3/ICE spacecraft. Analysis of the observations reveal that the IMF magnitude, which had declined to 4.7 nT in 1976, peaked in late 1982 (two years after solar maximum) at 9.0 nT and rapidly decreased during 1983-1984 to an intensity of 6.2 nT in early 1985. The IMF intensities are compared with the auroral AE index; the observed peak in strength during 1981-1983 is related to a 50 percent increase in substorm activity levels. A decrease in Parker spiral angle, revealing the existence of high-speed streams is detected in the declining phase of the solar cycle. Variations in the intensity of the IMF correlate with Mt. Wilson magnetograph measurements of full disk magnetic flux. Source regions for the evolution of solar wind and the IMF are proposed.

Slavin, J. A.↗
NASA NTRS1972

Solar wind

Conference on magnetic structure of interplanetary and solar magnetic fields and solar wind

Sonett, C. P.↗