Engineering topics

Russell, C. T.

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

At least 559 records · Page 31

NASA NTRS1979

Initial ISEE observations of the bow shock

ISEE 1 and 2 magnetic-field profiles across three terrestrial bow shock crossings are shown to illustrate the control of the bow shock structure and upstream waves by solar-wind conditions, especially by the direction of the interplanetary field. The quasi-perpendicular shocks examined have thicknesses of the order of a ion inertial length. Upstream waves observed for field directions of about 45 deg to the shock normal are observed to be carried back towards the bow shock by the solar wind, while propagating upstream at what appears to be the magnetosonic velocity. These studies are continuing.

Russell, C. T.↗

NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗

NASA NTRS1979

Position and shape of the Venus bow shock - Pioneer Venus Orbiter observations

Magnetometer data from the Pioneer Venus Orbiter is used to examine the position and shape of this planet's bow shock. Utilizing crossings identified on 86 occasions during the first 65 orbits a mean shock surface is defined for sun-Venus-satellite angles of 60-110 deg. Both the shock shape and variance in location are found to be very similar to the terrestrial case for the range in SVS angle considered. However, while the spread in shock positions at the earth is due predominantly to the magnetopause location varying in response to solar wind dynamic pressure, ionopause altitude variations can have little effect on total obstacle radius. Thus, the Cytherean shock is sometimes observed much closer to or farther from the planet than previously predicted by gasdynamic theory applied to the deflection of flow about a blunt body which acts neither as source nor sink for any portion of the flow.

Slavin, J. A.↗

NASA NTRS1979

A comparison of Pioneer Venus and Venera bow shock observations - Evidence for a solar cycle variation

Observations by the Venera 9 and 10 orbiters in 1975-76 have been used in previous studies to determine the mean location and shape of the Cytherean bow shock. In addition it has also been reported that the shock is found to be more distant from the planet above regions of the ionosheath where draped IMF field lines are oriented perpendicular to the flow as opposed to parallel. An examination of the dependence of shock altitude in the terminator plane on upstream IMF direction using 86 Pioneer Venus orbiter bow shock crossings in 1978-79 sets an upper limit on this asymmetry of 12% or approximately half that derived earlier from the Venera data. More significantly, the mean distance to the bow shock observed by Pioneer Venus Orbiter is 35% greater than was the case in 1975-76 near solar minimum. As the growth in effective obstacle radius is an order of magnitude larger than can be accounted for in terms of varying ionopause altitude due to all causes, these results strongly suggest that Venus can absorb significantly more of the incident solar wind plasma during solar minimum when EUV flux is low than during the current epoch in which maximum is approaching.

Slavin, J. A.↗

NASA NTRS1979

The Martian magnetic field

The paper presents an overview of the Martian magnetic field measurements and the criticisms made of them. The measurements of the Mars 2, 3, and 5 spacecraft were interpreted by Dolginov et al. (1976, 1978) to be consistent with an intrinsic planetary magnetic moment of 2.5 times 10 to the 22nd power gauss cu cm, basing this result on the apparent size of the obstacle responsible for deflecting the solar wind and an apparent encounter of the spacecraft with the planetary field. It is shown that if the dependence of the Martian magnetic moment on the rotation rate was linear, the estimate of the moment would be far larger than reported by Dolginov et al. An upper limit of 250 km is calculated for the dynamo radius using the similarity law, compared with 500 km obtained by Dolginov et al. It is concluded that the possible strength of a Martian dynamo is below expectations, and it is likely that the Mars dynamo is not presently operative.

Russell, C. T.↗

NASA NTRS1979

Lunar magnetic anomalies detected by the Apollo subsatellite magnetometers

Properties of lunar crustal magnetization thus far deduced from Apollo subsatellite magnetometer data are reviewed using two of the most accurate available magnetic anomaly maps, one covering a portion of the lunar near side and the other a part of the far side. The largest single anomaly found within the region of coverage on the near-side map correlates exactly with a conspicuous light-colored marking in western Oceanus Procellarum called Reiner Gamma. This feature is interpreted as an unusual deposit of ejecta from secondary craters of the large nearby primary impact crater Cavalerius. The mean altitude of the far-side anomaly gap is much higher than that of the near side map and the surface geology is more complex; individual anomaly sources have therefore not yet been identified. The mechanism of magnetization and the origin of the magnetizing field remain unresolved, but the uniformity with which the Reiner Gamma deposit is apparently magnetized, and the north-south depletion of magnetization intensity across a substantial portion of the far side, seem to require the existence of an ambient field, perhaps of global or larger extent.

Hood, L. L.↗

NASA NTRS1979

The solar wind interaction with Venus

The Pioneer Venus orbiter reveals that Venus has a well developed bow shock like the Earth's but on that is significantly weaker than the Earth's shock. The location of the bow shock is highly variable, more so than would have been expected for an obstacle of essentially fixed size. The altitude of the ionopause is also highly variable in response to changes in the solar wind. In the ionosphere, the field is often low. However, on some orbits, very large fields are seen as low as 150 km, and on most dayside orbits, thin magnetic structures of flux ropes are observed. At night, large fields are often observed which vary from orbit to orbit. Venus has a much smaller intrinsic magnetic moment than expected from scaling the terrestrial moment.

Russell, C. T.↗

NASA NTRS1979

Absorption of whistler mode waves in the ionosphere of Venus

It is shown that whistler mode waves from the ionosheath of Venus are absorbed by Landau damping at the dayside ionosphere boundary. This process heats the ionospheric electrons and it may provide an important energy input into the dayside ionosphere. Cyclotron damping of the waves does not occur in the same region. However, Landau damping of ionosheath waves is apparently not an important energy source in the nightside ionosphere. Impulsive events in the nightside ionosphere seem to fall into two classes: (1) lightning signals (near periapsis) and (2) noise, which may be caused by gradient or current instabilities.

Taylor, W. W. L.↗

NASA NTRS1979

Initial Pioneer Venus magnetic field results - Nightside observations

Initial observations by the Pioneer Venus magnetometer on the nightside of Venus frequently reveal moderately strong fields from 20 to 30 nanoteslas. However, there is little evidence that these fields arise from an internal dynamo, since they are mainly horizontal and vary from orbit to orbit. Determining a precise upper limit to the intrinsic moment awaits further processing. This limit is expected to be much less than 10 to the twenty-second gauss-cubic second.

Russell, C. T.↗

NASA NTRS1979

Evidence for lightning on Venus

Evidence for lightning on Venus obtained by the Pioneer Venus 1 Orbiter is presented. The first indications of lightning were detected by the electric field detector on board the Orbiter when the spacecraft periapsis, which is well within the ionosphere, moved into the night side of the planet. Impulsive wave signals were primarily detected at altitudes less than 25 km, and were found to be strongest at frequencies corresponding to propagation in the whistler mode, occurring at an average rate of about 0.5/sec. The signals were often observed during intervals of low and variable electron densities. It is tentatively concluded on the basis of the above observations that the impulsive events were caused by Venusian lightning.

Taylor, W. W. L.↗

NASA NTRS1979

Planetary magnetism

Recent data on planetary magnetism are reviewed, with attention given to information obtained by Mariner 10 at Mercury, from Venera 9 and 10 orbiting Venus, and Pioneer spacecraft flying past Jupiter. In addition, less recent magnetic measurements of Mars are reconsidered. Doubts about whether Mars has an active dynamo at present are mentioned, and further planetary magnetic assessments are suggested. In particular, the need to refine knowledge of multipole moments is stressed.

Russell, C. T.↗

NASA NTRS1979

Direct observation of a tangential electric field component at the magnetopause

Results are presented for direct, in situ measurements of the quasi-static electric field at and near the magnetopause, in the magnetosheath, bow shock, and solar wind, obtained by the ISEE-1 satellite. Both the large-scale average electric field and the fine-scale field observed during a magnetopause crossing show the existence of significant tangential electric field components on both sides of the magnetopause. The data in the satellite frame also show significant normal electric field components that point toward the magnetopause on both sides. The observed local level of power dissipation would correspond to a total power of 1 TW, if it existed over the entire front of the magnetopause.

Mozer, F. S.↗

NASA NTRS1979

Association of low-frequency waves with suprathermal ions in the upstream solar wind

Observations obtained upstream of the earth's bowshock with the LASL/MPI plasma instruments and the UCLA magnetometers on ISEE-1 and 2 have revealed a striking relationship between the presence of low-frequency fluctuations in solar wind density and field strength and the different types of distribution functions of upstream ions. Waves are absent when the ions have the beamlike distribution of the 'reflected' ions. Large-amplitude waves are present only in conjunction with the 'diffuse' ions, which are characterized by flat energy spectra and broad angular distributions. The waves are largely compressive, showing very good correlation between oscillations in magnetic field strength and plasma density.

Paschmann, G.↗

NASA NTRS1979

Initial ISEE magnetometer results - Shock observation

A selection of early measurements is used to illustrate the three advantages brought by ISEE to the study of natural collisionless shocks. These advantages are the ability to resolve most space/time ambiguity by means of simultaneous two-point measurements, instrumentation to make comprehensive field and particle observations covering all important quantities, and the capacity to record data at high time resolution. Magnetic-field records from shocks of various types are presented; the types of shock include laminar, supercritical, quasi-perpendicular, high-beta, and quasi-parallel. The spacing of the two spacecraft and the resolution of the system are employed to develop numerous kinematic descriptions of the shocks and the waves that compose and surround them. Data from a single particle experiment are correlated with field data for three cases to demonstrate the important role of comprehensive instrumentation.

Russell, C. T.↗

NASA NTRS1979

Initial Pioneer Venus magnetic field results - Dayside observations

Pioneer Venus magnetometer observations in the sunlit ionosphere indicate that the ionosphere is dynamic and very responsive to external solar wind conditions. Bow shock location, ionosphere location, the strength of the magnetic field just outside the ionopause, and the field strength in the ionosphere are found to be variable, and the properties of flux ropes in the ionospheric magnetic field are considered. Data on magnetic energy density and on magnetic field strength are presented.

Russell, C. T.↗

NASA NTRS1979

IMF orientation, solar wind velocity, and Pc 3-4 signals - A joint distribution

Separate studies using the same micropulsation data base in the period range 10-150 s have shown earlier that signal levels recorded during September, October, and November 1969 at Calgary correlated positively with both solar-wind alignment of the IMF and solar-wind speed, but each correlation contained enough scatter to allow for the influence of the other factor. In this report, joint correlations of velocity and field direction with parameters representing hourly distributions rather than minima of IMF orientation angle display the relative effect of the two agents on magnetic pulsation signal levels. The joint correlations reduce the overall scatter and show that solar-wind speeds above 200-300 km/s and angles between the IMF and the sun-earth line of less than 50-60 deg are associated with enlarged magnetic pulsation amplitudes. These threshold effects tend to support both the bow-shock origin and the Kelvin-Helmholtz amplification of daytime signal transients in the Pc 3, 4 period ranges.

Greenstadt, E. W.↗

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.↗