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At least 343 records · Page 19

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NASA NTRS1978

The radial gradients and collisional properties of solar wind electrons

The plasma electron detector on Mariner 10 is used to obtain measurements of electron density and temperature in the interplanetary medium between heliocentric distances of 0.85 and 0.45 AU. The observations show quantitatively that the core of the electron distribution function can be described as collisional at least for radial distances within 1 AU, since with a very few well-marked exceptions associated with high-speed streams, the Coulomb collisional momentum relaxation length is less than the density scale height at all times and all radial distances at which data were obtained. It is found that the Coulomb energy exchange collisions between the core and the (test) halo population are negligible. The power law exponent of the core temperature is about -0.3, whereas the halo temperature is almost independent of heliocentric distance.

Ogilvie, K. W.↗

NASA NTRS1978

Geomagnetic field fluctuations at synchronous orbit. I - Power spectra

ULF power spectra of geomagnetic variations at synchronous orbit are calculated for August 1974 on the basis of data from the UCLA triaxial fluxgate magnetometer on ATS 6. Emphasis is placed on the examination of the background spectrum, and therefore the diurnal differences and all relationships in magnetic activity as reflected in the Kp index. The average power spectrum at synchronous orbit is also compared with reported observations from the interplanetary medium, the magnetosheath, the region inside the magnetosphere near the magnetopause, and the ground.

Arthur, C. W.↗

NASA NTRS1978

Interplanetary scintillation at large elongation angles - Response to solar wind density structure

Synoptic interplanetary scintillation (IPS) index measurements at 34.3 MHz were obtained during May-December 1974 by means of the University of Iowa Cocoa Cross radiotelescope on a 'grid' of 150 selected radio sources covering solar elongation angles up to 180 deg. Over 80 of these sources displayed definite IPS, and the solar elongation dependence of the 34.3-MHz IPS index is consistent with the elongation of angle dependence measured at higher frequencies. Large enhancements of the IPS index are found to coincide with solar wind (proton) density increases greater than 10/cu cm. Correlation analysis confirms the IPS response to solar wind density and indicates that the events are due primarily to the corotating solar wind turbulent plasma structures which dominated the interplanetary medium during 1974.

Erskine, F. T.↗

NASA NTRS1977

Energetic solar flare particles and interplanetary shock waves

Estimates from hard X-ray measurements show that for many flares the bulk of the flare energy is released in the form of approximately 10-100-keV energy electrons. The interaction of these electrons with the solar atmosphere can produce the optical, UV, EUV, and radio emissions observed during the flare impulsive phase. In addition, explosive heating and evaporation of the chromosphere by these electrons can produce the roughly 10 million K soft X-ray plasma. For the large solar flares which produce interplanetary shock waves, the accelerated approximately 10-100-keV electron population may produce the heating and mass motion required for mass ejection and the formation of the shock wave. The shock wave can in turn accelerate ions and electrons to higher energy as it travels through the corona and interplanetary medium.

Lin, R. P.↗

NASA NTRS1977

Solar energetic particles below 10 MeV

The information on solar acceleration and coronal propagation contained in low energy solar particle observations must be extracted from the effects of propagation in a dynamic interplanetary medium and the proximity of the earth's magnetosphere. The resulting separation reveals long-lived coronal injection and strong spatial ordering of coronal propagation.

Roelof, E. C.↗

NASA NTRS1979

A theory of solar type 3 radio bursts

Energetic electrons propagating through the interplanetary medium are shown to excite the one dimensional oscillating two stream instability (OTSI). The OTSI is in turn stabilized by anomalous resistivity which completes the transfer of long wavelength Langmuir waves to short wavelengths, out of resonance with the electrons. The theory explains the small energy losses suffered by the electrons in propagating to 1 AU, the predominance of second harmonic radiation, and the observed correlation between radio and electron fluxes.

Goldstein, M. L.↗

NASA NTRS1979

Application of the minimum correlation technique to the correction of the magnetic field measured by magnetometers on spacecraft

Some aspects of the problem of obtaining precise, absolute determination of the vector of low magnetic fields existing in the interplanetary medium are addressed. In the case of a real S/C, there is always the possibility of a spurious field which includes the spacecraft residual field and/or possible field from the sensors, due to both electronic drifts or changes of the magnetic properties of the sensor core. These latter effects may occur during storage of the sensors prior to launching and/or in-flight. The reliability is demonstrated for a method which postulates that there should be no correlation between changes in measured field magnitude and changes in the measured inclination of the field with respect to any one of three fixed Cartesian component directions. Application of this minimum correlation technique to data from IMP-8 and Helios 1-2 shows it is appropriate for determination of the zero offset corrections of triaxial magnetometers. In general, a number of the order of 1000 consecutive data points is sufficient for a good determination.

Mariani, F.↗

NASA NTRS1978

Effects of the solar wind on magnetospheric dynamics: Energetic electrons at the synchronous orbit

A correlation of the observations of energetic electron fluxes at the synchronous orbit with the interplanetary medium and the behavior of energetic trapped radiation at the synchronous altitude were analyzed. Data covering the 1967 to 1978 interval were obtained by the ATS 1, ATS 5, and ATS 6 spacecraft. Long term (year) and short term (days) electron flux averages are found to correlate positively with corresponding averages of the solar wind velocity.

Paulikas, G. A.↗

NASA NTRS1978

Interplanetary magnetic holes - Theory

Magnetic holes in the interplanetary medium are explained as stationary nonpropagating equilibrium structures in which there are field-aligned enhancements of the plasma density and/or temperature. Magnetic antiholes are considered to be associated with depressions in the plasma pressure. In this model the observed changes in the magnetic field intensity and direction are due to diamagnetic currents that are carried by ions which drift in a sheath as the result of gradients in the magnetic field and in the plasma pressure within the sheath. The thickness of the sheaths that we consider is approximately a few ion Larmor radii. An electric field is normal to the magnetic field in the sheath. Solutions of Vlasov's equation and Maxwell's equations are presented which account for several types of magnetic holes, including 'null sheets,' that have been observed.

Burlaga, L. F.↗

NASA NTRS1979

Interplanetary phase scintillation and the search for very low frequency gravitational radiation

Observations of radio-wave phase scintillation are reported which used the Viking spacecraft having an earth-spacecraft link very similar to that which will be used in very low-frequency (VLF) gravitational-wave searches. The phase power-spectrum level varies by seven orders of magnitude as the sun-earth-spacecraft (elongation) angle changes from 1 to 175 deg. It is noteworthy that a broad minimum in the S-band (2.3 GHz) phase fluctuation occurs in the antisolar direction; the corresponding fractional frequency stability (square root Allan variance) is about 3 x 10 to the -14th for 1000-s integration times. A simultaneous two-frequency two-station observation indicates that the contribution to the phase fluctuation from the ionosphere is significant but dominated by the contribution from the interplanetary medium. Nondispersive tropospheric scintillation was not detected (upper limit to fractional frequency stability about 5 x 10 to the -14th). Evidently, even observations in the antisolar direction will require higher radio frequencies, phase scintillation calibration, and correlation techniques in the data processing, for detection of gravitational bursts at the anticipated strain amplitude levels of no more than 10 to the -15th.

Armstrong, J. W.↗

NASA NTRS1978

A review of the near-earth radiation environment

The spatial volume surrounding the earth out to 30 earth radii has been divided into the five regions known as the interplanetary medium, magnetosheath, plasma sheet, high-latitude magnetotail, and inner magnetosphere. In each region, the primary attributes of the particle populations and available models are described, and integral energy spectra covering the range from 10 to 10 billion eV are shown. The effects of the solar cycle on future projections are discussed.

Sawyer, D. M.↗

NASA NTRS1979

Spatial distribution of large-scale solar magnetic fields and their relation to the interplanetary magnetic field

The spatial organization of the observed photospheric magnetic field as well as its relation to the polarity of the IMF have been studied using high resolution magnetograms from the Kitt Peak National Observatory. Systematic patterns in the large scale field are due to contributions from both concentrated flux and more diffuse flux. The polarity of the photospheric field, determined on various spatial scales, correlates with the polarity of the IMF. Analyses based on several spatial scales in the photosphere suggest that new flux in the interplanetary medium is often due to relatively small photospheric features which appear in the photosphere up to one month before they are manifest at the earth.

Levine, R. H.↗

NASA NTRS1980

Overview on the study of the solar cycle from space

Recent insights into the workings of the solar system are reviewed as factors to be considered when formulating key questions to be answered during a large scale program to study the solar cycle. The main objectives of the Solar Cycle and Dynamics Mission are to determine the causes (physical origins and mechanisms) of the solar cycle and the effects of these mechanisms on the heliosphere, the vast region that includes the corona, interplanetary medium, and the terrestrial environment. The mission should be able to obtain synoptic data on solar variability associated with the cycle, and over at least a fraction of a single 11-year cycle.

Noyes, R. W.↗

NASA NTRS1980

Control of the Earth's electric field intensity through solar wind modulation of galactic cosmic radiation: Support for a proposed atmospheric electrical sun-weather mechanism

The ionospheric potential and galactic cosmic radiation, found to be inversely correlated with the solar wind velocity are examined as being germane to weather modification. Since the ionospheric potential is proportional to the fair weather electric field intensity and cosmic radiation is the dominant source of atmospheric ionization, it is concluded that the Earth's overall electric field varies in phase with atmospheric ionization and that the latter is modulated by the solar wind. A proposed mechanism, in which solar control of ionizing radiation influences atmospheric electrification and thus possibly cloud physical processes is discussed. An experimental approach to critically test the proposed mechanism through comparison of the temporal variation of the Earth's electric field with conditions in the interplanetary medium is outlined.

Markson, R.↗

NASA NTRS1979

Solar wind and magnetosphere interactions

The relationship between the magnetosphere and the solar wind is addressed. It is noted that this interface determines how much of the solar plasma and field energy is transferred to the Earth's environment, and that this coupling not only varies in time, responding to major solar disturbances, but also to small changes in solar wind conditions and interplanetary field directions. It is recommended that the conditions of the solar wind and interplanetary medium be continuously monitored, as well as the state of the magnetosphere. Other recommendations include further study of the geomagnetic tail, tests of Pc 3,4 magnetic pulsations as diagnostics of the solar wind, and tests of kilometric radiation as a remote monitor of the auroral electrojet.

Russell, C. T.↗

NASA NTRS1979

On the prediction of magnetospheric configuration

A simple model of magnetic flux transfer is reviewed along with empirical expressions for flux transfer rates based upon the auroral AL index and the eastward component of the interplanetary electric field. It is shown that the magnitude of the time integral of the AL index over isolated intervals of geomagnetic disturbance can be predicted from the the observed flux of southward interplanetary magnetic field lines incident on the front of the magnetosphere. Difficulties in the quantitative prediction of substorm onset time and intensity are discussed and magnetospheric stress index on both solar wind and ground based observations is proposed for this purpose. Finally, caveats concerning the use of both the AL index and interplanetary medium data in predicting the response of the magnetosphere to solar wind conditions are considered.

Slavin, J. A.↗

NASA NTRS1980

The electric potential of particles in interstellar space released from a nuclear waste payload

Mechanisms for charging a grain in the interplanetary medium include: (1) capture of solar wind electrons; (2) capture of solar wind protons; (3) ejection of electrons through the photoelectric effect due to the solar radiation; (4) escape of beta particles from beta emitters in the grain; and (5) escape of alpha particles from alpha emitters in the grain. The potentials on both nonradioactive and radioactive grains are considered with relation to particle size and time, and the distance from the Sun. Numerical results are presented where the waste mix is assumed to be PW-4b.

Williams, A. C.↗

NASA NTRS1980

Scientific results from the Pioneer Saturn encounter - Summary

The scientific results of the Pioneer Saturn encounter with Saturn are summarized. The Pioneer mission was designed to image the planet, its satellites and rings, and measure its particulate environment and the magnetic field and photon and charged particle radiation by means of 11 operational scientific instruments and its 2.293-GHz telemetry carrier signal. Principle results of the mission include the discovery of an additional ring and a previously unidentified satellite, the further characterization of the physical properties of Saturn and its magnetic field, and the description of the planetary magnetosphere. The successful completion of the mission demonstrated the ability of spacecraft such as Voyager 1 and 2 to survive the particle environments of Saturn's rings and trapped radiation environments, and Pioneer Saturn is expected to continue transmitting information on the interplanetary medium and the solar wind interaction with the interstellar medium until the mid-1980's.

Opp, A. G.↗