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NASA NTRS1978

Observations of the interplanetary sector structure up to heliographic latitudes of 16 deg - Pioneer 11

In the past, observations of the sector structure of the interplanetary magnetic field have been limited to a heliographic latitude of +/- 7.25 deg because spacecraft trajectories have consistently been in or near the ecliptic. The postencounter trajectory of Pioneer 11, which is now en route from Jupiter to Saturn, takes this spacecraft to much higher latitudes than have been previously explored. A study of the sector structure has in this connection been conducted during the ascent of Pioneer 11 to a maximum heliographic latitude of 16 deg. The Pioneer 11 observations demonstrate the presence in interplanetary space of an equatorial current sheet tilted at an angle of about 15 deg to the solar equatorial plane. Thus there is actually only one sector boundary in interplanetary space, not several, as would have been the case if the orientation had been meridional.

Smith, E. J.↗
NASA NTRS1978

Interplanetary magnetic field variations and the electromagnetic state of the equatorial ionosphere

The Esq phenomena were selected in order to examine the effect of the interplanetary magnetic field (IMF) on the ionospheric plasma and to obtain insight into the interplanetary ionospheric coupling processes. January-March 1973 interplanetary magnetic field data of Explorer 43, Huancayo ionograms, and surface equatorial magnetograms were used. The IMF observations from Explorer 43 in the form of 15-sec averages were examined around the time of disappearance of the Esq. The IMF z-component was observed to change from a negative to a positive value before the disappearance of the Esq in four events where simultaneous data were available. The general explanation is that the induced electric field becomes westward from a previous eastward direction, coinciding with the IMF z-component reversal. Thus, just before the Esq disappears, the magnetosphere is subjected to the westward electric field. If this field is impressed to the low-latitude ionosphere, the resultant electric field in the equatorial ionosphere changes from eastward (westward) to westward (eastward) in the daytime (nighttime).

Patel, V. L.↗
NASA NTRS1978

Interplanetary dust - Possible implications for comets and presolar interstellar grains

Interplanetary dust is important to studies of the origin of the solar system because it is material from comets and asteroids, the smallest surviving bodies from the early solar system. The fact that comets are the major suppliers of the millimeter meteoroids which produce optical meteors suggests that a significant fraction of the submillimeter portion of the meteoroid complex is also cometary material. While comets are probably the major source, it is important to remember that the dust presently impacting the earth was probably generated by a number of different parent bodies. The collection of interplanetary dust is considered and a description is presented of the physical properties of interplanetary dust, taking into account the structure, elemental composition, and mineralogy.

Brownlee, D. E.↗
NASA NTRS1979

Interplanetary magnetic field polarity and the size of low-pressure troughs near 180 deg W longitude

The relationship between interplanetary magnetic field polarity and the area of low pressure (300 mbar) troughs near 180 deg W longitude is examined. For most of the winters from 1951 to 1973, the trough size, as indicated by the vorticity area index, is found to be significantly greater when the interplanetary magnetic field is directed away from the sun than when the field is directed towards the sun. This relationship is shown to hold for various combinations of winters and for most months within a winter, and be most pronounced at the time when polarity was determined. It is suggested that the phenomenon is caused by merging of interplanetary magnetic field lines, when polarity is directed away from the sun, with geomagnetic field lines in the Northern Hemisphere (where these measurements were made), allowing energetic particle fluxes to have access to the north polar region

Wilcox, J. M.↗
NASA NTRS1979

Relationship between the growth of the ring current and the interplanetary quantity

Akasofu (1979) has reported that the interplanetary parameter epsilon correlates reasonably well with the magnetospheric substorm index AE; in the first approximation, epsilon represents the solar wind coupled to the magnetosphere. The correlation between the interplanetary parameter, the auroral electrojet index and the ring current index is examined for three magnetic storms. It is shown that when the interplanetary parameter exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, producing an abnormal growth of the ring current index.

Akasofu, S.-I.↗
NASA NTRS1979

Compositions of energetic particle populations in interplanetary space

Study of the compositions of energetic particle populations in interplanetary space is reviewed emphasizing observations of helium and heavier particles with energies below about 10 to 20 MeV/nucleon. Three dominant constituents of interplanetary particles are considered: solar flare particles, co-rotating particle streams, and a so-called 'anomalous cosmic ray' component. The recent discovery of a class of solar flare particle events with heavy elements indicates highly selective solar injection mechanisms. Observations of positive radial intensity gradients and anisotropies in co-rotating particle streams suggest the existence of large-scale interplanetary acceleration in a region extending from about 2 to 4 AU. Although present observations exclude the sun as a direct source of the 'anomalous cosmic ray' component, its origin is still debated.

Gloeckler, G.↗
NASA NTRS1979

Interplanetary medium data book, supplement, 1975 - 1978

Since the issurance of the Interplanetary Medium Data Book (NSSDC/WDC-A-R&S 77-04, 1977) which contains plots and listings of hourly average interplanetary field and plasma parameters covering the period November 27, 1963 through December 30, 1975, additional data are available which fill some 1975 data gaps and which extend the data coverage well into 1978. This supplement contains all the presently available data for the years 1975-1978, Interplanetary magnetic field (IMF) data are from the IMP 8 triaxial fluxgate magnetometer experiment. Derived plasma parameters are form the IMP 7 and IMP 8 instruments. Some of the early 1975 IMF data are from a HEOS 1 experiment.

King, J. H.↗
NASA NTRS1979

Interplanetary orbit determination

A general description of the Viking interplanetary orbit determination activity extending from launch to Mars encounter is given. The emphasis is on the technical fundamentals of the problem, basic strategies and data types used, quantitative results, and specific conclusions derived from the inflight experience. Special attention is given to the use of the spacecraft-based optical measurements and their first application as a principal navigational data type for an interplanetary mission. The optical-based orbit determination, in fact, was the primary contributor to the exceptional interplanetary navigation accuracy experienced by both Viking missions. The Viking application of optical orbit determination relied in large part on the technology developed and demonstrated by the Mariner 9 Optical Navigation Demonstration.

Rourke, K. H.↗
NASA NTRS1979

Interplanetary dust

Progress in the study of interplanetary dust during the past four years is reviewed. Attention is given to determinations of the relative contributions of interstellar dust grains, collisional debris from the asteroid belt and short-period comets to the interplanetary dust cloud. Effects of radiation pressure and collisions on particle dynamics are discussed, noting the discovery of the variation of the orbital parameters of dust particles at 1 AU with size and in situ measurements of dust density between 0.3 and 5 AU by the Helios and Pioneer spacecraft. The interpretation of the zodiacal light as produced by porous absorbing particles 10 to 100 microns in size is noted, and measurements of the Doppler shift, light-producing-particle density, UV spectrum, photometric axis and angular scattering function of the zodiacal light are reported. Results of analyses of lunar rock microcraters as to micrometeoroid density, flux rate, size distribution and composition are indicated and interplanetary dust particles collected from the stratosphere are discussed. Findings concerning the composition of fragile meteoroid types found as cosmic spherules in deep sea sediments are also presented.

Brownlee, D. E.↗
NASA NTRS1980

The plane of symmetry of interplanetary dust in the inner solar system

Observations of the zodiacal light from the space probes Helios 1 and 2 between 1.0 and 0.3 AU show - superimposed on the general radial dependence - a systematic variation of brightness and brightness distribution with position in the orbit which is caused by the inclination of the symmetry plane of interplanetary dust with respect to the ecliptic. By suitable choice of the observing geometry, the inclination and the ascending node of the symmetry plane can be determined directly from the data without recourse to model calculations. The resulting values of i equals 3.0 plus or minus 0.3 deg, Omega equals 87 plus or minus 4 deg are not compatible with a concentration of interplanetary dust to the invariable plane of the solar system. The data support the simple view that the distribution of interplanetary dust in the inner solar system is characterized throughout by one plane of symmetry and suggest that this plane extends to at least 1 AU.

Leinert, C.↗
NASA NTRS1980

Ions of Jovian origin observed by Voyager 1 and 2 in interplanetary space

Burst-like and long-lived ion fluxes (E greater than 30 keV) of Jovian origin have been observed in interplanetary space by the LECP instrument on the Voyager 1 and 2 spacecraft. Burst (few minute duration) events are observed at distances greater than 0.6 AU from Jupiter. These events are highly anisotropic and possess steep energy spectra, while long-lived (greater than 8 hour duration) events have relatively steady fluxes at low energies, strong anisotropies that decay with time, and a variable high energy component. Both types of events usually display simultaneous onsets and sharp cutoffs for all energies, an excess of atomic number Z not less than 6 particles compared to solar and interplanetary events, and particle flow directions pointed away from Jupiter along the local interplanetary magnetic field. The origin for the long-lived events appears to be inside the bow shock of the planet.

Zwickl, R. D.↗
NASA NTRS1979

Particle acceleration by propagating interplanetary shocks

The process of charged particle acceleration in interplanetary shocks has been simulated for typical parameters. Since space probe observations of charged particle fluxes are the principle means of inferring the action of an acceleration mechanism, the simulation was designed to follow particles backwards in time from a given observing point, usually 1 AU. This allowed a full diagnosis of which observed particles had interacted with an oncoming shock, where the interacting occurred, and by how much the energy had been changed by the shock interaction. Simple assumptions about the preshock energy spectrum allow the construction of a full temporal profile of the expected intensity, anisotropy, and energy spectrum. The simulations are apparently capable of reproducing the main features of the less than 10 MeV/nuc ion flux enhancements observed at interplanetary shocks using only a laminar interplanetary magnetic field, Archimidean spiral, and a spherical oblique shock with typical speed, strength, and shock normal-magnetic field angle.

Armstrong, T. P.↗
NASA NTRS1981

Bi-directional streaming of solar wind electrons greater than 80 eV - ISEE evidence for a closed-field structure within the driver gas of an interplanetary shock

In near time coincidence with the arrival of helium enriched plasma driving the shock wave disturbance of November 12-13, 1978, strong bi-directional streaming of solar wind electrons greater than about 80 eV was observed with Los Alamos instrumentation on ISEE 3. The streaming persisted for many hours simultaneously parallel and anti-parallel to the interplanetary magnetic field which was directed roughly perpendicular to the sun-satellite line. This example of bidirectional streaming cannot be explained by field line connection to the earth's bow shock or the outward propagating interplanetary shock which passed ISEE 3 approximately 16 hours earlier. The event is explained if the local interplanetary field was a part of a magnetic bottle rooted at the sun or a disconnected loop propagating outward.

Bame, S. J.↗
NASA NTRS1980

Solar and interplanetary dynamics; Proceedings of the Symposium, Harvard University, Cambridge, Mass., August 27-31, 1979

The symposium focuses on solar phenomena as the source of transient events propagating through the solar system, and theoretical and observational assessments of the dynamic processes involved in these events. The topics discussed include the life history of coronal structures and fields, coronal and interplanetary responses to long time scale phenomena, solar transient phenomena affecting the corona and interplanetary medium, coronal and interplanetary responses to short time scale phenomena, and future directions.

Dryer, M.↗
NASA NTRS1981

Pioneer 10 ultraviolet photometer observations of the interplanetary glow at heliocentric distances from 2 to 14 AU

An analysis is presented of the observed Pioneer 10 interplanetary data from 1972 to 1977, taking into account the interplanetary glow intensity observed by the Pioneer 10 UV photometer at sun-spacecraft distances of 2-14 AU. On the basis of the obtained data, it was determined that the background intensity for the 200-1400 A band pass of the photometer channel is about 40 + or - 10 R, and that the nearby interstellar density is 0.04 + or - 0.91 per ccm for hydrogen and about 0.01 + or - 0.002 per ccm for helium. Accordingly, the He/H number density is about 0.25 at large distances from the sun. The Pioneer 10 spacecraft is leaving the solar system in the downwind direction, while both Pioneer 11 and Voyager will leave in the upwind direction. The combined UV observations of the interplanetary glow will provide accurate results on the physical status of the inflowing interstellar gas and the variability of background radiation as well.

Wu, F. M.↗
NASA NTRS1981

Three-dimensional interaction of interplanetary shock waves with the bow shock and magnetopause - A comparison of theory with ISEE observations

The reported investigation is concerned with the propagation of the interplanetary shock waves in the solar wind and their three-dimensional interaction with the bow shock and magnetosheath. Formulae are deduced to predict the new position and orientation of the bow shock front after the interaction. To test the understanding of the interplanetary portion of the shock propagation, the obtained results are compared with observations on August 18, 1978, when both ISEE 1 and ISEE 3 were in the solar wind. Two examples of an interplanetary shock wave penetrating into the magnetosphere on October 4, 1978, and August 27, 1978, are examined, taking into account a simple model of the magnetosheath. The results agree with the observed values of the ISEE satellite data within experimental uncertainties.

Zhuang, H. C.↗
NASA NTRS1982

Jovian modulation of interplanetary electrons as observed with Voyagers 1 and 2

The release of magnetospheric electrons from Jupiter into interplanetary space is modulated by the Jovian rotation period. The Voyager 1 and 2 observations showed that the modulation period agrees on the average with the synodic period of Jupiter (9h 55m 33.12s), but over intervals of weeks it can differ from the synodic period by several minutes. The lack of exact synchronization is attributed to changes of the plasma population in the Jovian magnetosphere. The Jovian modulation appears to be a persistent feature of the interaction between the solar wind and the magnetosphere and the disappearance of the modulation away from Jupiter is attributed to interplanetary propagation conditions. This leads to the following limits on the diffuse coefficient for interplanetary electrons: kappa perpendicular is or = 8 x 10 to the 19th power sq cm/s and kappa parallel is or = 10 to the 21st power sq cm/s. Modulation was still detectable at 3.8 A.U. behind Jupiter in the far magnetotail. This requires a mean free path in the tail 0.75 A.U. and good field connection along the tail to Jupiter.

Schardt, A. W.↗
NASA NTRS1982

Plasma wave levels and IMF orientations preceding observations of interplanetary shocks by ISEE-3

Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle of the interplanetary magnetic field (IMF) to the shock normal at the time the shocks cross the spacecraft. It is shown that precursor wave noise level is correlated with field orientation and an extrapolated instantaneous orientation angle throughout the preshock observation interval for two contrasting active and quiet cases, and that intermediate, variable noise levels correspond to intermediate, variable IMF orientations. It is inferred that foreshocks are an intrinsic part of the structure of quasiparallel interplanetary shocks.

Greenstadt, E. W.↗