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Russell, C. T.

Publications and source records attributed to Russell, C. T..

At least 649 records · Page 36
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NASA NTRS1974

Observations of the internal structure of the magnetopause

Magnetic field, plasma flux, and ELF wave data have been studied for several encounters of Ogo 5 with the earth's magnetopause. In one case of a crossing in the near-earth region of the geomagnetic tail, the structure agreed closely with a simple Chapman-Ferraro type of model with nearly complete neutralization of the charge separation electric field. Departures from the simple structure were observed at other magnetopause crossings. One crossing revealed a well-defined double structure with a large change in field direction closer to the earth than the ion flux and field strength gradients. The thickness of the magnetopause often depended on whether the change in field strength, the change in field direction, or the change in ion flux was being considered. Bursts of ELF waves were occasionally observed at the magnetopause.

Neugebauer, M.↗
NASA NTRS1974

Plasma waves in the dayside polar cusp. II - Magnetopause and polar magnetosheath

During the outbound pass of Nov. 1, 1968, Ogo 5 sporadically encountered the low-altitude polar cusp at low magnetic latitudes. The spacecraft remained in the cusp beyond six earth radii, and it then traversed the interface region between the magnetospheric cusp and the magnetosheath. Two large scale discontinuities were detected in this sheath-cusp transition region, and several possible interpretations are evaluated here. At 1427 UT, local changes in magnetic field orientation and the variation in ULF magnetic power spectral density were typical of shifts detected at the magnetopause, although the spacecraft did not traverse a true boundary of warm plasma at this point. The second discontinuity, detected at 1456 UT, resembled a collisionless shock, and it was characterized by observations of intense, impulsive VLF electric field bursts and rapid local variations in both total ion flux and differential electron flux. The simplest interpretation is that Ogo 5 had traversed a standing shock within the sheath.

Scarf, F. L.↗
NASA NTRS1974

The solar wind and magnetospheric dynamics

The dynamic processes involved in the interaction between the solar wind and the earth's magnetosphere are reviewed. The evolution of models of the magnetosphere is first surveyed. The existence of the auroral substorm and the cyclical polar magnetic substorm is evidence that the magnetosphere is a dynamic system. The dynamic changes occurring in the magnetosphere, including erosion of the magnetopause, changes in the size of the polar cap, variations in the flaring angle of the tail, neutral point formation, plasma sheet motions, and the inward collapse of the midnight magnetosphere, are discussed. The cyclical variations of geomagnetic activity are explained in terms of the control of the solar wind-magnetosphere interaction by the north-south component of the interplanetary magnetic field. Present phenomenological models allow prediction of geomagnetic activity from interplanetary measurements, but modeling of detailed magnetospheric processes is still in its infancy.

Russell, C. T.↗
NASA NTRS1974

OGO-5 observations of the magnetopause

OGO-5 observations show not only that the average position of the magnetopause boundary moves in response to changes in dynamic pressure, but also that it moves in response to changes in the north-south component of the interplanetary field. Further, the boundary often oscillates about its average position as waves propagate along the boundary away from the nose region. The variation of the magnetic field through the boundary at times can be a simple rotation with no change in magnitude, and at other times can resemble a simple tangential discontinuity. However, it often displays complex patterns such as field enhancements on the magnetospheric side of the boundary or apparently uncorrelated field strength and direction changes. One particularly simple boundary crossing has been studied in detail with both positive ion data and magnetic field data. In this case, the electron and ion currents could be separately deduced and the structure agreed with that expected for a Chapman-Ferraro boundary with almost complete neutralization.

Russell, C. T.↗
NASA NTRS1974

Solar wind three; Proceedings of the Third Conference, Pacific Grove, Calif., March 25-29, 1974

Papers are presented relating to the study of solar abundances, the evolution of the solar wind, solar corona dynamics, solar wind interactions, and stellar winds. Some of the topics covered include the nuclear composition of cosmic rays, the solar wind as deduced from lunar samples, spectral characteristics of flares, numerical simulation of interplanetary shock ensembles, radial gradient of solar wind velocity from 1 to 5 AU, the enhancement of solar wind fluctuations with scale size near the proton gyroradius, solar wind-Venus interaction observed from magnetic field experiment on Mariner 10, and binary stellar winds. Individual items are announced in this issue.

Russell, C. T.↗
NASA NTRS1974

Instabilities connected with neutral sheets in the solar wind

A preliminary study is presented of two sets of data obtained by HEOS 1 and OGO 5 in the solar wind, which reveal the internal structure of two neutral sheets and their two-dimensional structure. HEOS 1 observations of the effects of the tearing mode instability in one of the sheets are described, including complicated structures connected with the sector boundary, sharp increases and decreases in the magnetic field intensity, and the presence of closed loops. HEOS 1 and OGO 5 observations of large oscillations due to plasma pressure imbalances are discussed, and it is concluded that an interchange instability may have been observed.

Formisano, V.↗
NASA NTRS1974

The permanent and induced magnetic dipole moment of the moon

Magnetic field observations with the Apollo 15 subsatellite have been used to deduce the components of both the permanent and induced lunar dipole moments in the orbital plane. The present permanent lunar magnetic dipole moment in the orbital plane is less than 1.3 times ten to the eighteenth power gauss-cu cm. Any uniformly magnetized near surface layer is therefore constrained to have a thickness-magnetization product less than 2.5 emu-cm per g. The induced moment opposes the external field, implying the existence of a substantial lunar ionosphere with a permeability between 0.63 and 0.85. Combining this with recent measures of the ratio of the relative field strength at the ALSEP and Explorer 35 magnetometers indicates that the global lunar permeability relative to the plasma in the geomagnetic tail lobes is between 1.008 and 1.03.

Russell, C. T.↗
NASA NTRS1973

Solar wind and substorm-related changes in the lobes of the geomagnetic tail

The relationship of the geomagnetic tail lobe energy density to solar wind dynamic pressure, the north-south component of the interplanetary magnetic field, and substorm expansion onsets is investigated. Enhanced lobe energy densities are observed to follow both southward turnings of the interplanetary magnetic field and solar wind dynamic pressure increases. An empirical relationship is developed relating the tail lobe magnetic energy density to the solar wind dynamic pressure by using data obtained when the interplanetary field was northward. Localized, off-center, or multiple-onset substorm expansion phases are shown to have little effect on the lobe magnetic field. A positive correlation is found between magnetosphere-wide substorm expansions and decreases in the lobe energy density. The positive correlation of the energy density with both the solar wind dynamic pressure and a southward interplanetary magnetic field and the positive correlation between magnetospheric substorm activity and lobe energy density decreases are demonstrated to be consistent with a phenomenological model of substorm behavior.

Caan, M. N.↗
NASA NTRS1973

The magnetotail and substorms

The tail plays a very active and important role in substorms. Magmetic flux eroded from the dayside magnetosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary flares more, the field strength in the tail increases, and the currents strengthen and move closer to the earth. Further, the plasma sheet thins and the magnetic flux crossing the neutral sheet lessens. The experimental evidence for these processes is discussed and a phenomenological or qualitative model of the substorm sequence is presented. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet.

Russell, C. T.↗
NASA NTRS1973

Comments on the paper 'The internal structure of the geomagnetic neutral sheet' by K. Schindler and N. F. Ness

Criticism of Schindler and Ness' (1972) multiple neutral point hypothesis, noting that there are several alternative interpretations of the distribution of magnetic field values observed by Explorer 34. It is shown that it is possible to interpret the tail magnetic field observations of Schindler and Ness without requiring neutral point encounters. On the other hand, if it is assumed that the observed field variations were due to neutral point encounters, there may be a single oscillating neutral point, or there may be multiple neutral points in time or in space.

Russell, C. T.↗
NASA NTRS1973

Active experiments, magnetospheric modification, and a naturally occurring analogue

Recently, a scheme has been proposed which would modify the magnetosphere by injecting plasma near the equator beyond the plasmapause and initiating wave-particle instabilities. The expected effects have been examined theoretically. Injection of plasma into this region is also a naturally occurring phenomenon produced by the cross-tail electric fields which are associated with geomagnetic activity. For further investigation of magnetospheric instabilities, the advantages of examining artificially injected plasma (control of time and location of injection and of the volume of plasma injected) contrast with the advantages of studying natural enhancements (no extra payload, frequent occurrence). Thus, the two types of experiments are complementary. In preliminary studies of natural plasma enhancements both ULF and ELF emissions have been observed. The ELF noise is consistent with generation by the electron cyclotron instability.

Kivelson, M. G.↗
NASA NTRS1973

Substorms in space - The correlation between ground and satellite observations of the magnetic field

Several of the events criticized by Akasofu (1972) are reexamined. It is concluded that there is no simple one-to-one relationship between polar magnetic substorms and magnetospheric substorms as defined by midlatitude magnetograms. It appears that in some cases polar magnetic substorms occur during the growth phase of a magnetospheric substorm. Magnetospheric observations are more systematically organized by midlatitude onsets than by auroral zone onsets. The determination of onset times is discussed together with the determination of substorm similarity, the phenomenological model of magnetic variations during magnetospheric substorms, the event of February 25, 1967, and the complex event of February 13, 1968.

Mcpherron, R. L.↗
NASA NTRS1973

Ion cyclotron waves observed in the polar cusp.

During the penetration by Ogo 5 of the low-latitude disturbed polar cusp region on Nov. 1, 1968, while a major magnetic storm was in progress, a variety of plasma wave activity was observed. Observations of waves with amplitudes less than 2% of the background magnetic field intensity and having frequencies between approximately 0.67 and 0.87 times the local proton gyrofrequency are described. The polarization of these waves indicates that they are propagating at an appreciable angle to the local geomagnetic field line direction. The source of these waves has not been determined, but currents and gradient drifts are suggested as possible agents.

Fredricks, R. W.↗
NASA NTRS1973

Satellite studies of magnetospheric substorms on August 15, 1968. IX - Phenomenological model for substorms.

Observations made during three substorms on August 15, 1968, are shown to be consistent with current theoretical ideas about the cause of substorms. The phenomenological model described in several preceding papers is further expanded. This model follows closely the theoretical ideas presented more quantitatively in recent papers by Coronti and Kennel (1972 and 1973).

Mcpherron, R. L.↗
NASA NTRS1973

Orbital mapping of the lunar magnetic field.

Examination of the lunar magnetic field as deduced from the orbital magnetometer data, with major emphasis on the general mapping of the lunar field over the orbit track of the Apollo 15 subsatellite. A detailed analysis of the data from a series of overflights of the Van de Graaff region at two different altitudes is also presented. This latter set of data makes it possible to determine the scale size of the region and the contrast between the remanent magnetization associated with the magnetic feature and its surroundings. The low altitude data from the Apollo 16 subsatellite, just prior to its impact into the lunar surface, are then examined. Data obtained while the moon was in the solar wind are used to construct a map which shows the lunar limb regions associated with the detection of limb compressions. This map is used to make qualitative inferences concerning the lunar remanent field in regions not covered by the contour maps.

Sharp, L. R.↗
NASA NTRS1973

Field-aligned currents, plasma waves, and anomalous resistivity in the disturbed polar cusp.

During the magnetic storm of November 1, 1968, the Ogo 5 spacecraft encountered the polar cusp region at low magnetic latitudes. We show that the region just outside the last closed field lines contained a warm magnetosheath plasma, magnetic field perturbations interpretable as field-aligned current layers, and electrostatic waves possibly due to plasma instabilities driven by these currents. Estimates of anomalous resistivity extrapolated along the field lines due to these electrostatic waves lead to estimates of field-aligned potential drops between Ogo 5 and the ionosphere on the order of 2 kV.

Fredricks, R. W.↗