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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1970

Magnetotail changes in relation to the solar wind magnetic field and magnetospheric substorms

An attempt is made to understand some of the magnetotail dynamics by using simultaneous observations from several satellites: Explorers 33 and 35 in the solar wind, IMP 4 in the near magnetotail (30 RE), ATS 1, and OGO 5 in the magnetosphere. It was observed that in the main lobes of the tail the magnetic field increases slowly when the interplanetary magnetic field turns southward, and can decrease slowly after a substorm. The plasma sheet changes indicate a thinning when the interplanetary magnetic field turns southward and an expansion when it turns northward. When combined with the plasma sheet expansion, which has been observed to follow a substorm, these results allow a schematic view of the relations between the changes in the orientation of the solar wind magnetic field, the substorms, and the changes in the tail parameters to be developed.

Aubry, M. P.↗
NASA NTRS1995

Heliomagnetic Latitude Dependence of Heliospheric Magnetic Field

ICE and IMP-8 magnetic field data from 1984 1988 were analyzed in a magnetic coordinate system defined by the orientation of the solar magnetic dipole. The heliomagnetic latitude dependence of the radial component of the magnetic field (Br) was then investigated in the range of magnetic latitudes from 60 above and below the heliospheric current sheet. Investigators found that Br reverses sign abruptly across the current sheet, consistent with solar magnetic field models, but inconsistent with the source surface models.

ICE↗
NASA NTRS1985

Effect of a fibril magnetic field on solar p-modes

The dispersion relation is obtained for acoustic plane waves that scatter coherently from an ensemble of parallel magnetic flux tubes when the wave vector is perpendicular to the flux-tube axis. When the magnetic flux tubes are distributed uniformly and possess radii that are small compared with the wavelength, the frequency can be calculated exactly. The waves are damped slightly due to a loss of coherence and are shifted downward or upward in frequency relative to a medium devoid of magnetic fibrils, depending primarily on whether the flux tubes are more or less dense than their surroundings. It is suggested that the influence of the fibril magnetic fields observed at the solar surface cannot be ignored in the interpretation of high-1 surface p-mode data.

Bogdan, T. J.↗
DOE OSTI2026

Enigmatic Line Broadening during Solar Flares: Magnetic Field Broadening?

The origin of the extreme broadening observed in chromospheric metal lines during solar and stellar flares—particularly Mg II h and k and Ca II H and K—remains poorly understood. These lines often display Lorentzian-like wings whose widths exceed standard Stark broadening predictions by factors of ∼30, with no known collisional mechanism capable of producing such enhancements. We posit that magnetic fields are responsible for this additional broadening, due to the increase of magnetic activity during flares. A magnetic field distribution of the form P(B) ∝ B −3 reproduces the observed Mg II profile wings while leaving H I Balmer lines and optically thin transitions largely unaffected. To explain the broadening using magnetic fields, the high-B tail can extend up to 10 6 G with extremely low probabilities where the filling factors are ≲10 −6 . We propose that observations of flares using spectropolarimetry can verify whether the anomalous broadening is from magnetic structures in flare ribbons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2003

The sun and heliosphere at solar maximum

Recent Ulysses observations from the Sun's equator to the poles reveal fundamental properties of the three-dimensional heliosphere at the maximum in solar activity. The heliospheric magnetic field originates from a magnetic dipole oriented nearly perpendicular to, instead of nearly parallel to, the Sun'rotation axis. Magnetic fields, solar wind, and energetic charged particles from low-latitude sources reach all latitudes, including the polar caps. The very fast high-latitude wind and polar coronal holes disappear and reappear together. Solar wind speed continues to be inversely correlated with coronal temperature. The cosmic ray flux is reduced symmetrically at all latitudes.

magnetic field solar winds galactic cosmic rays↗
NASA NTRS1989

Solar and stellar magnetic fields and atmospheric structures - Theory

Theoretical understanding of the role of magnetic fields in the formation of solar atmospheric structure is reviewed. The origin of the solar magnetic field, the dynamical behavior of the azimuthal field in the convective zone, the fibril state of the field in the photosphere, the formation of sunspots and prominences, and the spontaneous formation of current sheets in the bipolar field above the solar surface are addressed. The relation of the latter to coronal heating and flare formation is considered.

Parker, E. N.↗
NASA NTRS1975

Long-term evolution of solar sector structure

The large-scale structure of the solar magnetic field during the past five sunspot cycles (representing by implication a much longer interval of time) has been investigated, using the polarity (toward or away from the Sun) of the interplanetary magnetic field as inferred from polar geomagnetic observations. The polarity of the interplanetary magnetic field has previously been shown to be closely related to the polarity (into or out of the Sun) of the large-scale solar magnetic field. It appears that a solar structure with four sectors per rotation persisted through the past five sunspot cycles with a synodic rotation period near 27.0 days, and a small relative westward drift during the first half of each sunspot cycle and a relative eastward drift during the second half of each cycle. Superimposed on this four-sector structure there is another structure with inward field polarity, a width in solar longitude of about 100 deg, and a synodic rotation period of about 28 to 29 days. This 28.5-day structure is usually most prominent during a few years near sunspot maximum. Some preliminary comparisons of these observed solar structures with theoretical considerations are given.

Svalgaard, L.↗
NASA NTRS2000

Overview of the Solar Ultraviolet Magnetograph Investigation

Traditional magnetographs measure the solar magnetic field at the visible "surface" of the Sun, the photosphere. The Solar Ultraviolet Magnetograph Investigation (SUMI) is a design study for an instrument to measure the solar magnetic field higher in the atmosphere, in the upper chromosphere and in the transition region at the base of the corona. The magnetic pressure at these levels is much stronger than the gas pressure (in contrast to the situation at the photosphere), and so the field is much more dynamic. Observations in this region will significantly improve our understanding of the physical processes driving flares and heating in the Sun's upper atmosphere. The instrument will incorporate new technologies to achieve the polarization efficiencies required to isolate the magnetic lines (Civ at 155nm and MgII at 280nm) to be observed in the UV. We describe the scientific goals, the SUMI baseline design and the optical components that are being developed for a sounding rocket program.

West, Edward A.↗
NASA NTRS1974

Magnetic fields in the sun

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according as the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 G. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

Mullan, D. J.↗
NASA NTRS1974

Magnetic fields in the sun

The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

Mullan, D. J.↗
NASA NTRS1986

Effects of fibril magnetic fields on solar p-modes. II - Calculation of mode frequency shifts

The effect of magnetic flux tubes in the solar convection zone on p-mode oscillations is investigated analytically using WKB ray theory, extending the results of Bogdan and Zweibel (1985) to the case of propagation not perpendicular to the tubes. Results for the frequency shift in polytropic slabs with vertical or horizontal flux tubes are presented in graphs and discussed.

Zweibel, E. G.↗
NASA NTRS2003

Predicting the Structure of the Solar Corona During the December 4, 2002 Total Solar Eclipse

The solar magnetic field plays a key role in determining coronal. The principal input to MHD models is the observed solar magnetic field. 3D MHD models can be used to compare with eclipse and coronograph images, SOHO images (LOSCO, EIT), Ulysses and WIND spacecraft data, and interplanetary scintillation (IPS) measurements. MHD computations can tell us about the structure of the corona. Eclipses can help us to verify the accuracy of the models. 4 December, 2002 total eclipce: visible in the southern hemisphere (South Atlantic, southern Africa, Indian Ocean, and Australia). Total in center Angola is at 06:00 UT.

Mikic, Zoran↗
NASA NTRS1995

Structure of magnetic field in the solar wind

This work is concerned with empirical data on magnetic field in the solar wind in frame of a concept of dissipative solar wind, developed in papers (Solar Wind 7 Conf., Pergamon Press, 1992, 165 and 1992 STEP/5th COSPAR Coll. Pergamon Press, 1994, 117; 235; 803). Interplanetary magnetic fields should be classified with respect to their origin. It is very important for all the theoretical problems from the necessity to specify correctly boundary and initial conditions: the magnetic field must be sewed with its source. One should select the field, connected directly with the Sun (stretched out from it), and the field of moving electric currents. It occured central in discussion about the velocity of Alfven waves, probably warming up the solar wind, relative to the Sun, the magnetic field and solar wind plasma. The selection problem corresponds to an inverse problem and obviously has no single solution. The dissipative model of the solar wind introduce the slipping and leakage of plasma relative to magnetic field. There are no 'interplanetary current sheets' in it. But temporal fluctuations from the filamentation of electric currents play the key role. As a whole, the new concept requires the re-interpretation of main objects in the interplanetary magnetic field.

Chertkov, A. D.↗
NASA NTRS1977

Possible origins of time variability in Jupiter's outer magnetosphere. I - Variations in solar wind dynamic pressure. II - Variations in solar wind magnetic field

Attention is given to the effect of changes in the dynamic pressure of the solar wind on the structure of a centrifugally driven planetary wind from Jupiter. It is suggested that dynamic pressure variations can induce a transition between a super-Alfvenic wind and a sub-Alfvenic wind breeze on Jupiter's dayside. This could possibly account for the observed large-scale changes in the structure of Jupiter's outer magnetosphere. An attempt is then made to conceptually merge planetary wind models of Jupiter's outer magnetosphere with reconnection models of Jupiter's outer magnetosphere.

Coroniti, F. V.↗
NASA NTRS2000

SUMI: The Solar Ultraviolet Magnetograph Investigation

A major focus of solar physics is the measurement of the temporal and spatial variability of solar magnetic fields from the photosphere into the lower corona, together with the study of how their behavior produces the dynamic phenomena in this region such as flares and Coronal Mass Injection (CMEs). Considerable success has been achieved in the characterization of the full vector field in the photosphere, where P, the ratio of the gas pressure to the magnetic pressure, is greater than or equal to 1. At higher levels in the atmosphere where beta is less than 1, the magnetic field (through the Lorentz force) controls the structure and dynamics of the solar atmosphere, and rapid changes in structure with release of energy become possible. However, observations of the field at these higher levels have proven to be difficult, placing a serious limitation on our understanding of the physical processes occurring there. This poster will discuss the Solar Ultraviolet Magnetograph Investigation (SUMI), a hardware development study for an instrument capable of measuring the polarization in ultraviolet lines of C IV and Mg II formed in the transition region and upper chromosphere. We are currently developing optical technologies necessary to build an instrument that will achieve a major advance in performance over that of earlier attempts (e.g., SMM/UVSP). Initially configured as a sounding rocket payload, such a UV magnetograph would allow us to make exploratory measurements extending the observation of solar magnetic fields into new and dynamic regimes. This work is supported by NASA through the SEC Program in Solar Physics and the program for Technology Development for Explorer Missions and Sofia.

Davis, John M.↗