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Russell, C. T.

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

At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

ISEE observations of flux transfer events at the dayside magnetopause

Magnetic field measurements from the ISEE 1 and 2 spacecraft are examined in the vicinity of the magnetopause near local noon on a typical pass when the magnetosheath field is southward. The data clearly show evidence for patchy impulsive reconnection. The flux transfer rate for these events is at least of the order of 1-2 times 10 to the 12th Maxwells per second, and possibly greater. This rate is similar to rates deduced for magnetopause erosion events. Not only are these observations relevant to the substorm process, but the impulsive nature of the flux transfer events leads to boundary oscillations that could also be the source of long period magnetic pulsations in the outer magnetosphere.

Russell, C. T.↗
NASA NTRS1979

The interaction of the solar wind with Mars, Venus and Mercury

The history of investigation of the solar wind interaction with Mars, Venus, and Mercury is reviewed, and our knowledge on this interaction for each of the three planets is compared. The primary objective is to gain insight into the basic physical mechanisms operative in the earth's magnetosphere from a study of (the somewhat different) magnetospheres of the planets under consideration. Mercury and Venus have significant dipole moments which play an important part in solar wind interaction. The Martian magnetic moment appears to be too weak to influence solar wind interaction. As expected, the bow shock of Mercury and the earth are quite similar since the magnetic moment of each is sufficient to stand off the solar wind. The shocks of Venus and Mars are also similar, but the Venusian shock lies much closer to the planet than the Martian shock. Both Mercury and Venus show evidence of substorm-like field and particle behavior, but with clear differences in the time scale.

Russell, C. T.↗
NASA NTRS1979

Initial Pioneer Venus magnetometer observations

Initial Pioneer Venus magnetometer observations reveal a highly dynamic interaction between the solar wind and the ionosphere and a very weak and possibly absent intrinsic magnetic field. The bow shock position and the altitude of the ionopause vary markedly from day to day. The magnetic pressure in the magnetosheath just outside the ionopause is in near balance with the thermal ionospheric pressure inside. Although the ionospheric magnetic field strength is generally low, occasional enhancements are observed with field strengths exceeding that in the magnetosheath. These bundles of magnetic flux, or flux ropes, may be convected to the night side ionosphere in which large field strengths (compared to the dayside) are common. The magnetic field magnitude and direction in this region are quite variable, suggesting that the field is not due to an intrinsic planetary source, but rather due to induced ionospheric currents. The magnetic moment is probably much less than 10 to the 22nd Gauss-cu cm.

Russell, C. T.↗
NASA NTRS1978

Initial ISEE magnetometer results - Magnetopause observations

Magnetic-field profiles across the magnetopause are examined which were obtained by the ISEE 1 and 2 spacecraft on four passes when the spacecraft separation was only a few hundred kilometers. The velocity of the magnetopause is found to be highly irregular, ranging from 4 to over 40 km/s and varying on a shorter time scale than required for a spacecraft to cross the boundary. The thickness of the magnetopause is estimated to range from 500 to over 1000 km. Clear evidence for field-line reconnection is discerned in data obtained when the magnetosheath field was southward. This evidence consists of flux-transfer events in which reconnection begins and ends on a time scale of minutes or less, leading to oscillations in the position of the magnetopause.

Russell, C. T.↗
NASA NTRS1978

Ion acoustic stability analysis of the earth's bow shock

A marginal stability criterion for ion acoustic waves is applied to the analysis of five thin bow shock crossings observed by OGO-5; the observations began with the satellite in the magnetosheath. The assumption of marginally stable ion acoustic wave generation in the shock ramp provides the basis for determining the thickness of the magnetic gradients for subcritical, quasi-perpendicular shock features.

Greenstadt, E. W.↗
NASA NTRS1978

Evidence for a non-random magnetization of the moon

An approximate inversion, using a specific model, of Apollo subsatellite vector magnetometer data has provided estimates for the locations, scale sizes, and magnetization characteristics of strongly magnetized lunar crustal materials across a portion of the lunar far side. The nearly model-independent local bulk directions of magnetization, while otherwise random, exhibit a tendency to lie in or near planes perpendicular to the present lunar spin axis. The apparent existence of such a preferred plane of magnetization must be regarded as unfavorable for proposed local, presumably random sources of large-scale, coherent magnetization and implies that any assumed internal magnetizing dipole or external linear magnetizing field must also have been oriented mainly perpendicular to the present spin axis. The otherwise random orientations of these vectors when projected onto the equatorial plane suggests a simple explanation for the negligible lunar global dipole moment.

Hood, L.↗
NASA NTRS1978

On the apparent source depth of planetary magnetic fields

Two simple assumptions regarding the ratios of the strengths of the field contributions of the multipole moments of the terrestrial magnetic field at its effective source depth are used to examine the consistency between the apparent source depths for the magnetic fields of Mercury and Jupiter and the present understanding of their interior structure. Both fields are consistent with the present understanding. However, the comparison would be facilitated by further measurements of the magnetic fields at both planets, especially at Mercury.

Elphic, R. C.↗
NASA NTRS1978

The statistical magnetic signature of magnetospheric substorms

Daily magnetograms from a midlatitude network of geomagnetic observatories were used in the analysis of approximately 1800 substorm events, and the characteristic magnetic signatures of magnetospheric substorms both on the ground and in space were determined. Auroral electrojet (AE) indices and individual magnetograms at different local times in the auroral zone and at midlatitudes were analyzed with reference to onsets, and superposed epoch averages of individual magnetograms and AE indices confirm the local time magnetic substorm signatures. Superposed epoch averages of the interplanetary magnetic field (IMF) associated with the onsets demonstrates both a distinct southward component prior to the onsets and a dependence of the substorm amplitude on the integrated preceding southward IMF flux. Superposed epoch averages of the tail lobe magnetic field magnitude and vector components are discussed.

Caan, M. N.↗
NASA NTRS1978

The magnetic field of Mars - Mars 3 evidence reexamined

Dolginov et al. (1972, 1973) presented evidence for a Mars magnetic field based on Mars 2 and 3 measurements. This evidence is somewhat complex, based on a combination of arguments including the position of the bow shock, the identification of magnetopause crossings, and the simultaneous behavior of the plasma and the field. The evidence rests most heavily on one pass of Mars 3 on December 1, 1972 from which Dolginov et al. deduce the direction and orientation of the magnetic moment of Mars. It is the purpose of the present note that there is no reason to suppose that Mars 3 penetrated the Mars magnetosphere on this pass, that because of their locations all other putative magnetopause crossings are suspect and that the effective obstacle height is coincident with the height of the Mars ionosphere to within the accuracy of our knowledge of the proper scaling law for planetary bow shocks.

Russell, C. T.↗
NASA NTRS1978

The magnetic field of Mars - Mars 5 evidence re-examined

The putative magnetotail encounters of the Mars 5 spacecraft cannot be scaled to the terrestrial magnetopause. Furthermore, the magnetic field during these claimed magnetotail encounters tends to be wrapped around the planet rather than rooted in it. There is no conclusive evidence that the Mars 5 spacecraft ever entered a Martian magnetosphere. The upper limit to the Martian magnetic moment is estimated to be 2 by 10 to the 21st power gauss-cu cm, or 0.000025 times the terrestrial magnetic moment.

Russell, C. T.↗
NASA NTRS1978

The Third General Scientific Assembly of the International Association of Geomagnetism and Aeronomy - Special sessions of auroral processes

Methods of timing magnetic substorms, the rapid fluctuations of aurorae, electromagnetic and electrostatic instabilities observed on the field lines of aurorae, the auroral microstructure, and the relationship of currents, electric field and particle precipitation to auroral form are discussed. Attention is given to such topics as D-perturbations as an indicator of substorm onset, the role of the magnetotail in substorms, spectral information derived from imaging data on aurorae, terrestrial kilometric radiation, and the importance of the mirror force in self-consistent models of particle fluxes, currents and potentials on auroral field lines.

Russell, C. T.↗
NASA NTRS1978

The magnetization of the lunar crust as deduced from orbital surveys

A two-dimensional magnetic anomaly map of a region of intense crustal magnetization near Van de Graaff crater has been constructed from Apollo 15 and 16 subsatellite vector magnetometer observations. The mapping method used limits coverage to relatively low altitudes (65-80 km) over the Van de Graaff region along the Apollo 15 track and over the central far side highlands along the Apollo 16 track; a simple differencing technique was used to remove external noise contributions. An approximate inversion of this map using a surface plate model for source region geometry has revealed at least four different sources. No correlation between the lateral locations of these source regions and surface morphology was found; the directions of magnetization seem to be unrelated except for a strong north-south depletion. A rough antipodal correlation of the two most strongly magnetized regions yet mapped on the moon with the Imbrium and Orientale basins gives mild support to the ejecta deposit hypothesis suggested by Strangway et al. (1973) for formation of anomaly source regions.

Hood, L. L.↗
NASA NTRS1978

A comparison of contour maps derived from independent methods of measuring lunar magnetic fields

Computer-generated contour maps of strong lunar remanent magnetic fields are presented and discussed. The maps, obtained by previously described (Eliason and Soderblom, 1977) techniques, are derived from a variety of direct and indirect measurements from Apollo 15 and 16 and Explorer 35 magnetometer and electron reflection data. A common display format is used to facilitate comparison of the maps over regions of overlapping coverage. Most large scale features of either weak or strong magnetic field regions are found to correlate fairly well on all the maps considered.

Lichtenstein, B. R.↗
NASA NTRS1977

High altitude observations of Birkeland currents

Several models of field-aligned currents (Birkeland currents) in the magnetosphere are discussed, and high altitude observations of these currents, carried out with the aid of highly eccentric earth-orbiting spacecraft of the OGO and IMP series, are reviewed. The essential roles of Birkeland currents are identified: they relieve charge imbalances, transmit stresses, and lead to particle acceleration anomalous resistivity.

Russell, C. T.↗
NASA NTRS1977

Characteristics of the association between the interplanetary magnetic field and substorms

The geomagnetic response to changes in the orientation of the interplanetary magnetic field (IMF) has been investigated for 18 IMF events. These events consisted of clear southward shifts of the IMF when the IMF Bz(GSM) component had been northward for more than two hours. It was found that when the IMF thus shifted southward and remained southward for at least two hours, a magnetospheric substorm always ensued. Several properties of this subsequent geomagnetic activity were determined to be associated with IMF parameters. The amplitude of auroral negative bays was confirmed to be a function of the southward IMF flux preceding the onsets. Auroral bay activity was also observed to cease abruptly coincident with permanent northward recoveries in the IMF. Finally, it was observed that many of the ground expansion onsets were associated with either IMF northward fluctuations or partial northward recoveries, which is interpreted as indicative of the existence of a class of IMF-triggered substorms.

Caan, M. N.↗
NASA NTRS1977

On the relative locations of the bow shocks of the terrestrial planets

The observed bow shock encounters at Mercury, Venus and Mars are least square fit using the same technique so that their sizes and shapes can be intercompared. The shock front of Mercury most resembles the terrestrial shock in shape, and the shock stand off distance is consistent with the observed moment. The shapes of the Venus and Mars shock fronts more resemble each other than the earth's and the stand off distances are consistent with direct interaction of the solar wind with the ionosphere on the dayside. The Venus shock is closer to the planet than the Mars shock suggesting more absorption of the solar wind at Venus.

Russell, C. T.↗