Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “IMP”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Carbon-poor solar flare events

Energetic particle flux enhancements over the period October 1973 - December 1977 were surveyed using ULET sensor on the IMP-8 spacecraft. During the four year period the most extreme periods of Fe enrichment compared to oxygen were during solar flare events in February 1974 and May 1974. In these same events, the carbon abundance with respect to oxygen was significantly depleted when compared with a value C:0 is approximately 0.45:1 for typical solar flares. These observations, taken together with previously reported He-3 enrichment in these events, give strong evidence for the importance of a wave-particle interaction in the pre-injection heating of the ambient matter.

Mason, G. M.↗
NASA NTRS1979

Latitudinal beaming of Jupiter's low frequency radio emissions

By comparing RAE-1 and IMP-6 satellite measurements of Jupiter's radio emission near 1MHz with recent Voyager-1 and 2 observations in the same frequency range, the properties of the low frequency radiation pattern over a 10 deg range of latitudes with respect to the Jovian rotation equator can be studied. These observations, which cover a wider latitudinal range than is possible from the earth, are consistent with many aspects of earlier ground-based measurements used to infer a sharp beaming pattern for the decameter wavelength emissions. Marked, systematic changes are found in the statistical occurrence probability distributions with system 3 central meridian longitude as the jovigraphic latitude of the observer changes over this range. Simultaneous observations by the two Voyager spacecraft suggest that the instantaneous beam width may be no more than a few degrees at times. The new hectometer-wave results can be interpreted in terms of a narrow, curved sheet at a fixed magnetic latitude into which the emission is beamed to escape the planet.

Alexander, J. K.↗
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 NTRS1979

Interplanetary sector boundaries, 1971 - 1973

Eighteen interplanetary sector boundary crossings observed at 1 AU by the magnetometer on the IMP-6 spacecraft are discussed. The events were examined on many different time scales ranging from days on either side of the boundary to high resolution measurements of 12.5 vectors per second. Two categories of boundaries were found, one group being relatively thin and the other being thick. In many cases the field vector rotated in a plane from one polarity to the other. Only two of the transitions were null sheets. Using the minimum variance analysis to determine the normals to the plane of rotation, and assuming that this is the same as the normal to the sector boundary surface, it was found that the normals were close to the ecliptic plane. An analysis of tangential discontinuities contained in 4-day periods about the events showed that their orientations were generally not related to the orientations of the sector boundary surface, but rather their characteristics were about the same as those for discontinuities outside the sector boundaries.

Klein, L.↗
NASA NTRS1978

Simultaneous measurements of energetic protons and electrons in the distant magnetosheath, magnetotail, and upstream in the solar wind

The paper investigates the presence of energetic protons and electrons in the magnetopause/magnetosheath region of the tail as well as upstream from the bow shock in the solar wind, estimates the energy densities of protons and electrons, and assesses the relationship between the energies associated with these particles and the dayside reconnection region. The study is based on measurements in experiments on the IMP 7 and 8 spacecraft. It is shown that the energetic protons and electrons are present not only in the distant magnetosheath but also in the upstream solar wind and inside the magnetosphere. These protons carry much more energy (x50) than the electrons, and most likely originate inside the magnetosphere. Thus there appears to be little connection between the presence of these energetic particles in the distant magnetosheath region and the dayside reconnection region.

Krimigis, S. M.↗
NASA NTRS1978

The radial diffusion coefficient of 1.3 - 2.3 MeV protons in recurrent proton streams

The paper presents anisotropy measurements of 1.3-2.3 MeV protons in the interplanetary space during recurrent events for which the radial intensity variation is measured within the radial range from about 0.3 to about 4 AU for the period from June, 1973 through April, 1976. The simultaneous measurements of the diffusive anisotropy and the radial gradient are used to make a direct estimate of the interplanetary radial diffusion coefficient, which is independent of any particular solution of the propagation equation. IMP 7 and 8 is required to be sunward of the earth and hence outside of the magnetosphere; if both spacecraft are sunward, measurements from the one farthest from the magnetosphere are used. The resulting values for the radial diffusivity coefficient near 1 AU lie in the range (3 to 9) x 10 to the 20th sq cm/sec, corresponding to scattering mean free paths between 0.03 and 0.1 AU with a mean of 0.06 AU.

Mewaldt, R. A.↗
NASA NTRS1978

Structure of current sheets in magnetic holes at 1 AU

Current density profiles in several types of interplanetary magnetic holes have been calculated using high-resolution Imp 6 magnetic field data (12.5 vector measurements/s), assuming that the currents flow in planar sheets and that the magnetic field varies only in the direction normal to the sheet. The planarity was verified in four holes which were observed by two suitably spaced spacecraft. Four types of simple magnetic holes are discussed, in which B varies nearly monotonically on each side of the hole. In two of the holes, B varies in intensity but not in direction as a result of currents normal to B. In the other two holes, B changes in both magnitude and direction as a result of currents both normal and parallel to B. The observed structures are found to be qualitatively consistent with the models of Burlaga and Lemaire (1978). Examples of complex irregular magnetic holes are also presented, and they are shown to contain multiple current sheets in which currents flow parallel to one another at various angles with respect to B. There is no model of such magnetic holes at present.

Fitzenreiter, R. J.↗
NASA NTRS1978

IMF structures between 0.3 and 1 A.U. - A comparison of two-spacecraft observations

Interplanetary-magnetic-field observations by Helios 1 and IMP 8 have been compared for a period of time (corresponding to four solar rotations) in which the radial and latitudinal separations between spacecraft, respectively, ranged between 0 and 0.69 AU and 0 and 14.5 degrees. The correspondence between macrostructural features is good even when the observing spacecraft are located at opposite sides of the solar equatorial plane. Unipolar regions of the interplanetary magnetic field are confirmed as steady-state, corotating structures and are also mostly consistent with a quite regular extension of the field polarities of the observed coronal holes. There are, however, interesting examples of recurrent unipolar regions which are not associated with the recurrent pattern of high-velocity streams. A comparison of two field enhancements suggests that these structures do not experience significant modifications with the heliocentric distance.

Villante, U.↗
NASA NTRS1979

Proton-driven electromagnetic instabilities in high-speed solar wind streams

Electromagnetic instabilities of the field-aligned, right-hand circularly polarized magnetosonic wave and the left-hand circularly polarized Alfven wave driven by two drifted proton components are analyzed for model parameters determined from Imp 7 solar wind proton data measured during high-speed flow conditions. Growth rates calculated using bi-Lorentzian forms for the main and beam proton as well as core and halo electron velocity distributions do not differ significantly from those calculated using bi-Maxwellian forms. Using distribution parameters determined from 17 measured proton spectra, we show that considering the uncertainties the magnetosonic wave may be linearly stable and the Alfven wave is linearly unstable. Because proton velocity distribution function shapes are observed to persist for times long compared to the proton gyroperiod, the latter result suggests that linear stability theory fails for proton-driven ion cyclotron waves in the high-speed solar wind.

Abraham-Shrauner, B.↗
NASA NTRS1979

Observations of plasma depletion in the magnetosheath at the dayside magnetopause

In a set of 17 low- to mid-latitude crossings of the dayside and near-dayside magnetopause, Imp 6 plasma measurements show 11 cases of decreases in magnetosheath density just outside the boundary which are consistent with plasma depletion owing to magnetic flux tube compression as the field becomes draped against the magnetopause. Pressure anisotropies in the sense pressure perpendicular to the field direction greater than pressure parallel to it are a predicted result of the plasma depletion and field compression, and such anisotropies are observed. Application of the mirror instability criterion, which predicts growth of slow mode magnetoacoustic waves for values of the ratio between the cited pressures greater than a critical value, suggests that dayside magnetosheath plasma is usually unstable. One of the seventeen cases shows long-period waveforms in the 100-s density data that are 180 deg out of phase with simultaneous waveforms in the magnetic field strength. These data are interpreted as the signature of slow mode magnetoacoustic waves.

Crooker, N. U.↗
NASA NTRS1979

Magnetosheath electrostatic turbulence

The spectrum of electrostatic wave turbulence in the terrestrial magnetosheath is investigated. Measurements of electric and magnetic field fluctuations in the range 20 Hz to 200 kHz were made by two 16-channel spectrum analyzers on board the IMP 6 satellite. It is found that the electrostatic wave spectra generally consist of three components, which may occur in any combination: a low frequency component which shows a decrease in spectral density with increasing frequency and which is associated with the bow shock wave, a high frequency component identified with electron plasma oscillations and an intermediate frequency component. The minimum wavelength of electrostatic waves is found to be about 0.1 km, with intensity of from 0.01 to 1.0 mV/m. Electric field polarization has been found to be parallel to the local magnetic field direction, implying the presence of longitudinal electrostatic wave modes, electron plasma oscillations and ion sound waves.

Rodriguez, P.↗
NASA NTRS1979

Magnetic fields in flowing magnetotail plasmas and their significance for magnetic reconnection

A statistical study is made of the magnetic field components that occur in the presence of high-velocity flows. Results are reported for a statistical analysis of 324 intervals of intense bulk plasma flows in the plasma sheet of the geomagnetic tail, measured by the Imp 6 spacecraft. A pronounced tendency for southward fields to be associated with tailward flow more often than with earthward flow yields support for the merging concept, though not in its simplest form. Histograms of 15.36-s averages of vector magnetic field measurements during plasma flows reveal no significant changes in the distribution of beta-y between earthward or tailward plasma flow directions.

Caan, M. N.↗
NASA NTRS1979

Observations of significant magnetosheath antisolar energy flow

Results from the Imp 7 satellite reveal antisolar magnetosheath ion flows of 10 to the 18th to 10 to the 20th ergs/sec when they are integrated over the observed flow cross-sectional area. These results extend, in energy and spatial regions sampled, the earlier work of West and Buck (1976). The results show the existence of energized protons in the downstream magnetosheath which at energies above 50 keV carry an energy flow of the same magnitude as the extrapolated (above 1 keV) results of Baker and Stone (1977). Possible sources of the energy flow include dissipation processes due to a magnetopause electric field, leakage of magnetospheric particles through the magnetopause into the magnetosheath, bow shock acceleration, and magnetosheath acceleration.

Williams, D. J.↗
NASA NTRS1978

The relative abundances of the elements silicon through nickel in the low energy galactic cosmic rays

Measurements of the relative abundances of the elements Si through Ni in galactic cosmic rays in the energy interval 72 to 450 MeV/nucleon are reported based on data collected by a cosmic-ray telescope on the IMP 8 satellite. The measured abundances are compared with propagation calculations using various distributions of path lengths. It is found that the measurements favor an exponential distribution of path lengths truncated at short path lengths. The source abundances of Si, Ca, Fe, and Ni derived by extrapolating the measured abundances back to the source are shown to be comparable to the solar-system abundances. The relevance of the measurements of Sc through Mn to the Mn-54 radioactive decay is examined.

Garcia-Munoz, M.↗
NASA NTRS1978

Charge and energy spectra of heavy cosmic rays at intermediate energies

The energy spectra and the charge composition of the primary elements C, O, Ne, Mg, and Si have been measured in both the low-energy and high-energy modes of the University of Chicago telescope on board the IMP 8 spacecraft. Combining both modes of analysis yields differential energy spectra for each element from about 50 MeV/nucleon to about 1 GeV/nucleon. The charge ratios with respect to oxygen are found to be energy independent over this interval and are consistent with the results of cosmic-ray propagation and solar-modulation calculations. The relative abundances obtained are in substantial agreement with previous investigations in this energy regime.

Garcia-Munoz, M.↗
NASA NTRS1978

Acceleration of H, He, and CNO ions and electrons observed in the earth's magnetospheric environment

The probability of simultaneous observation of ion pulses on the IMP 7 and 8 satellites in the earth's magnetotail was analyzed. It was found that the simultaneous observation was rather infrequent unless the two satellites were separated by a distance less than about 5 earth radii. It is suggested that this separation is a measure of the linear dimension of the regions where magnetic field line annihilation took place at a rapid rate and the observed ions with energy equal to or greater than 100 keV ions were accelerated. The annihilation rate was estimated to be equal to the Alfven velocity of the local plasma medium.

Fan, C. Y.↗
NASA NTRS1978

Spatially dominated solar particle events 1972-1976

Low-energy solar-particle data from the APL/JHU experiments on IMP 7 and 8 during 50 solar rotations between September 1972 and May 1976 are examined, and it is found that spatial gradients which are nearly independent of particle rigidity and species dominate the time histories. There are 57 rounded events with gradients on each side, 17 spatially dominated decays of flare-associated temporal events, and 9 broad minima. These events fill about 70% of the total time period, and about 70% are associated with solar-wind streams. The e-folding lengths of the gradients average about 20 deg heliographic longitude, and the rounded events have soft spectra and are helium-rich. These events are consistent with coronal propagation from a central source by a mechanism independent of particle species and energy.

Gold, R. E.↗
NASA NTRS1978

The relationship between Jovian electrons and solar wind stream structure

Near-earth observations of above-0.22-MeV Jovian electrons by the APL/JHU experiments on IMP-7 and 8 during 1972-1975, a period of stable recurrent solar wind, reveals 19 of 26 events in good association with solar wind streams. This pattern of positive correlation with solar wind streams is also observed in 3-6 MeV data from 1965-1972 during well-defined electron events. During their pre-encounter periods Pioneers 10 and 11 were nearly radially aligned with Jupiter and direct magnetic connection was highly unlikely. Jovian electrons above about 5 MeV in the UCSD experiments on Pioneers 10 and 11 were anticorrelated with solar wind velocity from about 3-4 AU until encounter. Reconstructions of the large-scale interplanetary magnetic field suggest that the near-earth events result from direct connection with the Jovian magnetotail and corotation of quasi-trapped populations while for Pioneer events electrons propagate out from the magnetosphere to a solar wind stream interaction, in along the interaction, then in to Pioneer on undisturbed field lines.

Gold, R. E.↗