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At least 1,387 records · Page 77
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NASA NTRS1975

The large-scale magnetic field in the solar wind

A large-scale, three dimensional magnetic field in the interplanetary medium with an expected classical spiral pattern to zeroth order is discussed. Systematic and random deviations which are expected are treated. The sector structure which should be evident at high latitudes is examined. Interplanetary streams are discussed as determining the patterns of magnetic field intensity. It was proposed that the large-scale spiral field can induce a meridional flow which might alter the field geometry somewhat. The nonuniformities caused by streams will probably significantly influence the motion of solar and galactic particles. It was concluded that knowledge of the 3-dimensional field and its dynamical effects can be obtained by in situ measurements by a probe which goes over the sun's poles. Diagrams of the magnetic fields are given.

Burlaga, L. F.↗
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 field configuration in the magnetotail near 60 earth radii

The magnetic field line configuration in the geomagnetic tail near 60 earth radii is examined on the basis of nearly 3 years of magnetometer data from the lunar-orbiting Explorer 35 satellite. The magnetotail field line characteristics inside the plasma sheet and in the high-latitude tail, i.e., outside the plasma sheet, are separately examined. In the high-latitude tail the magnetic field lines systematically diverge in both longitudinal (east-west) and latitudinal (north-south) directions; the divergence angle between field lines near the dusk flank and those near the dawn flank is about 14 deg, but the divergence along the Z direction is only about 8 deg. The degree of divergence is found to be greater in the evening side than in the morning side and greater in the northern tail than in the southern tail. Inside the plasma sheet the field lines deviate by about 19 deg from the sun-earth line, and the spatial distribution of the field line deviation does not have any systematic tendency.

Meng, C.-I.↗
NASA NTRS1974

Mariner 10 interplanetary magnetic field observations - Preliminary results

The results being reported consist primarily of distributions of the hourly average field large-scale properties and fluctuation characteristics by solar rotation for the time interval 7 November 1973 to 5 April 1974, as well as the variation of the daily average field as a function of the distance from the sun between 1 and 0.46 AU. The data indicate that the interplanetary magnetic field (IMF) generally increases with decreasing distance from the sun; the field magnitude distribution broadened as Mariner 10 approached Mercury; the positive sector of the IMF tended to rotate progressively toward the theoretical spiral field direction; and magnitude fluctuations increased with increasing distance from the sun, while vector field fluctuations tended to decrease. Data on radial dependence of the IMF were not consistent with theoretical models and did not coincide with extrapolations based on data gathered by Mariner 4 and 5. Comprehensive graphs and charts illustrate all the data obtained by Mariner 10.

Behannon, K. W.↗
NASA NTRS1975

Comparison of high-latitude and mid-latitude ionospheric electric fields

Simultaneous measurements of the F region electric field by the incoherent scatter technique have been made at Chatanika, Alaska (65.1 deg N, 147.5 deg W), and Millstone Hill, Massachusetts (42.6 deg N, 71.5 deg W), on July 18-19 and Aug. 7-8, 1973. Good correlation was observed in the time variation of the perpendicular electric field at the two stations. Magnetic conditions for these days were relatively quiet with some variations evident from the high-latitude magnetograms and the Chatanika radar, but no distinct effect appeared on the mid-latitude magnetograms. Since magnetospheric electric fields are thought to be the source of high-latitude electric fields such as those observed at Chatanika, the good correlation in the perpendicular electric field for the two stations indicates that the magnetospheric originated electric fields have an appreciable effect down to at least L equals 3.2.

Carpenter, L. A.↗
NASA NTRS1975

The generation of magnetic fields in astrophysical bodies. X - Magnetic buoyancy and the solar dynamo

The magnetic field appearing as bipolar magnetic regions at the surface of the sun represents the lines of force from a general azimuthal field of the order of 100 gauss somewhere beneath the surface. The amplification time, as a consequence of the nonuniform rotation, is of the order of 10 years. But magnetic buoyancy brings the azimuthal field up through much of the convective zone in a time rather less than 10 years, raising the question of where the azimuthal field can be retained long enough to be amplified. We show that magnetic fields can be retained for long periods of time in the stable radiative region beneath the convective zone, but unfortunately the solar dynamo cannot function there because turbulent diffusion is an essential part of its operation. The only possible conclusion appears to be that the dynamo operates principally in the very lowest levels of the convective zone at depths of 150,000 km or more, where the gas density is 0.1 g/cu cm, and the fields are limited to 50 gauss.

Parker, E. N.↗
NASA NTRS1975

The magnetic field of Mercury. I

An updated analysis and interpretation are presented of the magnetic field observations obtained during the Mariner 10 encounter with the planet Mercury on March 29, 1974. The combination of data relating to position of the detached bow shock wave and magnetopause and the geometry and magnitude of the magnetic field within the magnetosphere-like region surrounding Mercury lead to the conclusion that an internal planetary field exists with dipole moment approximately 5.1 times 10 to the 22nd G per cu cm. The dipole axis has a polarity sense similar to that of earth and is tilted 7 deg from the normal to Mercury's orbital plane. The magnetic field observations reveal a significant distortion of the modest Hermean field by the solar wind flow and the formation of a magnetic tail and neutral sheet which begins close to the planet on the night side. Presently, an active dynamo mechanism in the planetary interior appears to be favored in the interpretation of the field origin.

Ness, N. F.↗
NASA NTRS1975

Effect of electric fields on the daytime high-latitude E and F regions

We have obtained solutions of the coupled continuity, momentum, and energy equations for NO(+), O(+), and O2(+) ions for conditions appropriate to the daytime high-latitude E and F regions. Owing to the rapid increase of the reaction O(+) + N2 yielding NO(+) + N with ion energy, high-latitude electric fields and consequent perpendicular-E x B drifts deplete O(+) in favor of NO(+). For electric field strengths less than about 10 mV/m the depletion of O(+) is small, and the altitude profiles of ion density are similar to those found at mid-latitudes. However, for moderate electric field strengths (50 mV/m), NO(+) is substantially increased in relation to O(+) and becomes an important ion throughout the F region. For large electric fields (200 mV/m), NO(+) completely dominates the ion composition to at least 600 km, decreasing at high altitudes with a diffusive equilibrium scale height. Since the overall F region electron density decreases markedly with increasing electric field strength, it appears that high-latitude, daytime electron density troughs are directly related to the presence of ionospheric electric fields.

Schunk, R. W.↗
NASA NTRS1975

Observations of Mercury's magnetic field

Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

Ness, N. F.↗
NASA NTRS1976

The passage of a distorted velocity field through a cascade of airfoils

An analysis has been developed to predict the unsteady force and moment generated by the passage of a timewise periodic total pressure distortion through an arbitrary cascade of airfoils. The mathematical formulation of this analysis is based on the assumption that the magnitudes of the timewise fluctuations of the variables which describe the flow field are small compared to their time average values. This assumption permits the development of a linear unsteady perturbation analysis about a steady flow field. In addition to this linearization assumption the fluid medium is assumed to be incompressible and inviscid. The mathematical development begins by decomposing the velocity field surrounding an infinite cascade of airfoils into its irrotational and rotational components. The rotational component is associated with an upstream unsteady total pressure distortion and is defined in terms of the vorticity field associated with the distortion pattern. The irrotational component is further decomposed into a steady and unsteady part. A combined analytical and numerical procedure has been developed to solve the field equations which govern the rotational and irrotational velocity fields. Results of this analysis show a strong influence of mean loading on the unsteady force generated by the passage of a one dimensional gust through a cascade of compressor blades.

Adamczyk, J. J.↗
NASA NTRS1976

Analysis of field size distributions, LACIE test sites 5029, 5033, and 5039, Anhwei Province, People's Republic of China

A study was made of the field size distributions for LACIE test sites 5029, 5033, and 5039, People's Republic of China. Field lengths and widths were measured from LANDSAT imagery, and field area was statistically modeled. Field size parameters have log-normal or Poisson frequency distributions. These were normalized to the Gaussian distribution and theoretical population curves were made. When compared to fields in other areas of the same country measured in the previous study, field lengths and widths in the three LACIE test sites were 2 to 3 times smaller and areas were smaller by an order of magnitude.

Podwysocki, M. H.↗
NASA NTRS1975

Lunar remnant magnetic field mapping from orbital observations of mirrored electrons

A technique is described for mapping areas of lunar surface magnetism by observing ambient low-energy electrons from lunar orbit with a detector that is sectored to distinguish directions of arrival with respect to the ambient magnetic field and the lunar surface. It is noted that the ambient electrons provide a probe along the ambient magnetic-field lines down to the lunar surface for remote sensing of the presence of surface fields. Unlike direct magnetometer measurements, this probe does not require low altitude or a very stable ambient field in order to map the occurrence regions of such fields. Preliminary maps generated for the surface magnetic areas underlying the orbit of the Particles and Fields Satellite deployed from Apollo 16 are presented to demonstrate the feasibility of this technique.

Mccoy, J. E.↗
NASA NTRS1976

Magnetic dipole moment of a spherical shell with TRM acquired in a field of internal origin

The acquisition of thermoremanent magnetization (TRM) by a cooling spherical shell is studied for internal magnetizing dipole fields, using Runcorn's (1975) theorems on magnetostatics. If the shell cools progressively inward, inner regions acquire TRM in a net field composed of the dipole source term plus a uniform field due to the outer magnetized layers. In this case, the global dipole moment and external remanent field are nonzero when the whole shell has cooled below the Curie point and the source dipole has disappeared. The remanent field outside the shell is found to depend on the thickness, radii, and cooling rate of the shell, as well as the coefficient of TRM and the intensity of the magnetizing field. Some implications for the moon's remanent dipole moment are discussed.

Srnka, L. J.↗
NASA NTRS1976

High-beta effects and anomalous diffusion in plasmas expanding into magnetic fields

A metallic laser-produced plasma is allowed to expand transversely into an applied magnetic field, under conditions where the typical ion cyclotron radius is much larger, and the electron cyclotron radius much smaller, than the experimental dimensions. A stationary background plasma may also be present. Initially, the flow energy density exceeds (B squared/8 times pi), where B is the ambient magnetic field. Magnetic coil probes, Langmuir probes, and microwave diagnostics are used to study the plasma-field interaction. Field compression at the leading edge and field exclusion within the expanding plasma are seen. The diagnostic measurements and comparison with a theoretical model demonstrate plasma turbulence and anomalously high diffusion of field into the expanding plasma.

Koopman, D. W.↗
NASA NTRS1976

Numerical computations of Orbiter flow fields and heating rates

Numerical computations of flow fields around an analytical description of the Space Shuttle Orbiter windward surface, including the root of the wing leading edge, are presented to illustrate the sensitivity of these calculations to several flow field modeling assumptions. Results of parametric flow field and boundary layer computations using the axisymmetric analogue concept to obtain three-dimensional heating rates, in conjunction with exact three-dimensional inviscid floe field solutions and two-dimensional boundary layer analysis - show the sensitivity of boundary layer edge conditions and heating rates to considerations of the inviscid flow field entropy layer, equilibrium air versus chemically and vibrationally frozen flow, and nonsimilar terms in the boundary layer computations. A cursory comparison between flow field predictions obtained from these methods and current Orbiter design methods has established a benchmark for selecting and adjusting these and future design methodologies.

Goodrich, W. D.↗
NASA NTRS1976

A proposed concept for the extraction of energy stored in magnetic or electric fields in space

It is known that enormous energy resources associated with electric, magnetic, gravitational, and other fields exist in space. It is also known that the major difficulty in 'tapping' this energy arises from the extremely low density level at which this energy exists. An analytical study has been made of a particular scheme that appears promising for an efficient utilization of some of these energy resources in propulsion. The principle involves the exchange of energy between a fluctuating magnetic field and a velocity field of electrically conducting fluid in turbulent motion located onboard a spacecraft. Under certain conditions the total energy of the turbulent flow field onboard the spacecraft can be increased and this increase appears in the form of Joulean heat. The utilization of the fluctuating part of the magnetic field, in the form of Joulean dissipation (because of its random character) does not introduce any drag on the spacecraft. The application appears promising for flights in the vicinity of Jupiter and other planets. The rate at which energy is gained by the conducting fluid is of the order of 100 watts when the rms value of the fluctuating magnetic field strength is about 1 gauss.

Papailiou, D. D.↗
NASA NTRS1976

Electric field statistics for close lightning return strokes near Gainesville, Florida

The salient properties of the electric field intensity from first and subsequent lightning return strokes in the 0-25 km distance range near Gainesville, Fla., are presented, including electric field wave shape versus distance, initial peak rise time versus distance, rise time histograms, initial peak magnitude versus distance, normalized (to 100 km) initial peak magnitude histograms, normalized initial peak magnitude versus rise time, ramp starting time versus distance, and field at 170 microsec versus distance. The mean normalized initial peak field for first return strokes was 9.9 V/m and for subsequent strokes, 5.7 V/m. The maximum measured values of normalized initial peak field were about 30 V/m. The largest field recorded at 170 microsec was about 25 kV/m generated by a first stroke within 0.5 km. Return strokes were found to lower a typical charge of the order of 1 C in 170 microsec.

Tiller, J. A.↗
NASA NTRS1976

Acceleration of auroral electrons in parallel electric fields

Rocket observations of auroral electrons are compared with the predictions of a number of theoretical acceleration mechanisms that involve an electric field parallel to the earth's magnetic field. The theoretical models are discussed in terms of required plasma sources, the location of the acceleration region, and properties of necessary wave-particle scattering mechanisms. We have been unable to find any steady state scatter-free electric field configuration that predicts electron flux distributions in agreement with the observations. The addition of a fluctuating electric field or wave-particle scattering several thousand kilometers above the rocket can modify the theoretical flux distributions so that they agree with measurements. The presence of very narrow energy peaks in the flux contours implies a characteristic temperature of several tens of electron volts or less for the source of field-aligned auroral electrons and a temperature of several hundred electron volts or less for the relatively isotropic 'monoenergetic' auroral electrons. The temperature of the field-aligned electrons is more representative of the magnetosheath or possibly the ionosphere as a source region than of the plasma sheet.

Kaufmann, R. L.↗