Engineering topics

Slavin, J. A.

Publications and source records attributed to Slavin, J. A..

At least 127 records · Page 7

NASA NTRS1986

Giacobini-Zinner magnetotail - Ice magnetic field observations

A well developed magnetotail with a diameter of about 10,000 km has been revealed 7800 km downstream of the nucleus of Comet Giacobini-Zinner by International Cometary Explorer magnetic field observations. The tail is composed of two lobes of opposite magnetic polarity that are separated by an approximately 1500 km-thick plasma sheets. The field magnitude increases by a factor of 2 between the outer portions of the lobe and the central regions, where peak fields of about 60 nT were measured. Flaring is lowest in the high field regions of the central tail and greatest in the outer portions of the lobes, where minimum variance analyses on the magnetopause crossings furnishes flare angles of 20-40 deg. The Alfven field line draping model of type I cometary tails is confirmed by these observations.

Slavin, J. A.↗

NASA NTRS1986

Statics and dynamics of Giacobini-Zinner magnetic tail

The data gathered by the International Cometary Explorer during its traversal of Comet Giacobini-Zinner's tail are subjected to stress balance requirements, yielding estimates of unmeasured quantities. It is noted that the comet's tail is embedded in an ionosheath whose static pressure is nearly equal to the solar wind stagnation pressure, leading to a large lobe field strength. A systematic variation is found in the ion temperature across the tail, implying the variation of the pickup velocity of new ions. Axial stress balance yields an expression for the strength of the lobe field which reveals weak variation with axial distance.

Siscoe, G. L.↗

NASA NTRS1986

Neutral sheet crossings by ISEE-3 in the distant magnetotail

Magnetic field data from ISEE-3 in the distant magnetotail at crossings of the field reversal (or neutral sheet) region were analyzed to determine the instantaneous direction of the normal component Bz at the crossing. A crossing identified as being almost always tailward of the steady-state X-line was selected. Data for 1 hr are discussed to illustrate difficulties. One particular smooth crossing shows that complicated microstructure can occur in times less than 1 min. Averaging over long times may eliminate essential information. Inspection of the magnetic field data at the highest resolution, however, shows that the direction of the plasma sheet flows and the sense of Bz across the neutral sheet do not always agree with the reconnection models. Rather, they indicate that the low latitude boundary layer may play a significant role in the dynamics of the magnetotail.

Heikkila, W. J.↗

NASA NTRS1986

Analysis of the Giacobini-Zinner bow wave

The cometary bow wave of P/Giacobini-Zinner has been analyzed using the complete set of ICE field and particle observations to determine if it is a shock. Changes in the magnetic field and plasma flow velocities from upstream to downstream have been analyzed to determine the direction of the normal and the propagation velocity of the bow wave. The velocity has then been compared with the fast magnetosonic wave speed upstream to derive the Mach number and establish whether it is supersonic, i.e., a shock, or subsonic, i.e., a large amplitude wave. The various measurements have also been compared with values derived from a Rankine-Hugoniot analysis. The results indicate that, inbound, the bow wave is a shock with M = 1.5. Outbound, a subsonic Mach number is obtained, however, arguments are presented that the bow wave is also likely to be a shock at this location.

Smith, E. J.↗

NASA NTRS1986

The heliospheric current sheet - 3-dimensional structure and solar cycle changes

The reversal in polarity of the interplanetary current sheet/sector structure is investigated during the recent solar maximum. Multipoint observations by ISEE-3 and Pioneer 11 show that a simple two sector or occasional four sector structure persisted throughout the maximum and out to distances of 10 AU. The polarity reversal occurred between March 1979 and October 1980, without any indication of an abrupt transition that might permit a more precise timing. The reversal coincided approximately with the reversal in the sun's polar cap fields. The current sheet appeared to be highly inclined during the ascending and descending phases of the solar cycle but was apparently too complex to describe as a simple inclined current sheet during solar maximum.

Smith, E. J.↗

NASA NTRS1986

Neutral sheet crossings by ISEE-3 in the distant magnetotail

The magnetic field data from ISEE-3 in the distant magnetotail at crossings of the field reversal (or neutral sheet) region are analyzed to determine the instantaneous direction of the normal component B(z) at the crossing. Crossings in the middle of the aberrated magnetotail near the apogee A2 of the first deep-tail orbit of ISEE-3 in January-February, 1983 were selected. Data for an interval of one hour is discussed at length to illustrate some of the difficulties that can occur. One particular smooth crossing at 15:56 UT, February 4, 1983, shows that complicated microstructure can occur in times shorter than one minute; averaging over long times may eliminate essential information for this purpose. By inspecting the magnetic field data at the highest resolution, however, it is shown that the direction of the plasma sheet flows and the sense of B(z) across the neutral sheet do not always agree with the reconnection models. Rather, they indicate that the low latitude boundary layer may play a significant role in the dynamics of the magnetotail.

Heikkila, W. J.↗

NASA NTRS1986

Shocks and storm sudden commencements

Recent gains in understanding the relationship between shocks and storm sudden commencements (SSCs) are reviewed with emphasis on spacecraft observations in general and ISEE-3 observations in particular. The topics discussed include the relation of SSC amplitude to increase in solar wind pressure, the inference of shock properties from SSC amplitudes, SSCs as representative of the transient response of the magnetosphere to a step function input, and magnetic storms accompanying shocks.

Smith, E. J.↗

NASA NTRS1986

Solar wind-magnetosphere coupling and the distant magnetotail - ISEE-3 observations

ISEE-3 Geotail observations are used to investigate the relationship between the interplanetary magnetic field, substorm activity, and the distant magnetotail. Magnetic field and plasma observations are used to present evidence for the existence of a quasi-permanent, curved reconnection neutral line in the distant tail. The distance to the neutral line varies from absolute value of X = 120 to 140 R/sub e near the center of the tail to beyond absolute value of X = 200 R/sub e at the flanks. Downstream of the neutral line the plasma sheet magnetic field is shown to be negative and directly proportional to negative B/sub z in the solar wind as observed by IMP-8. V/sub x in the distant plasma sheet is also found to be proportional to IMF B/sub z with southward IMF producing the highest anti-solar flow velocities. A global dayside reconnection efficiency of 20 + or - 5 percent is derived from the ISEE-3/IMP-8 magnetic field comparisons. Substorm activity, as measured by the AL index, produces enhanced negative B/sub z and tailward V/sub x in the distant plasma sheet in agreement with the basic predictions of the reconnection-based models of substorms. The rate of magnetic flux transfer out of the tail as a function of AL is found to be consistent with previous near-earth studies. Similarly, the mass and energy fluxes carried by plasma sheet flow down the tail are consistent with theoretical mass and energy budgets for an open magnetosphere. In summary, the ISEE-3 Geotail observations appear to provide good support for reconnection models of solar wind-magnetosphere coupling and substorm energy rates.

Slavin, J. A.↗

NASA NTRS1986

Twisting of the geomagnetic tail

Theory and models indicate that the IMF causes the magnetotail to produce an observable twist, predicting that the torque should bring the north lobe south of the GSM xy plane on one flank of the magnetotail, and the south lobe north of the plane on the other flank. In this paper, ISEE-3 geotail observations are compared with simultaneously made IMP 8 IMF observations supplemented by inferred IMF B(y) polarities to demonstrate the IMF-induced magnetotail twist. The results indicate that twisting is the single most important factor accounting for observations of the north lobe south of the GSM xy plane and the south lobe north of the plane. The value of the observed magnetotail twist about its aberrated axis is about 18 deg.

Sibeck, D. G.↗

NASA NTRS1985

An ISEE 3 study of average and substorm conditions in the distant magnetotail

Both average and substorm conditions in the distant magnetotail were investigated using ISEE 3 magnetic field and plasma observations. The diameter of the tail, the strength of the lobe magnetic fields, and their dependence on downstream distance were all found to agree well with the flaring tail models of magnetopause geometry and pressure balance. The gradual filling of the lobes by mantle plasma reported in previous ISEE 3 studies were further investigated, and the results were found to be in qualitative agreement with leaky magnetopause model of Pilipp and Morfill (1978). The variations of plasma parameters with X + or -Y, and AE in the plasma sheet were examined. At all distances, the greatest tailward flow speeds were found to be directly proportional to the embedded southward B(z). THe magnitudes of tailward V(x) and southward B(z) are directly proportional to the level of substorm activity near the earth as measured by the AE index.

Slavin, J. A.↗

NASA NTRS1985

Magnetic field properties of the distant magnetotail magnetopause and boundary layer

Models incorporating merging between dayside magnetosheath and magnetosphere field lines predict the location of the magnetotail boundary layer and bending of magnetotail field lines in the direction of the IMF. Previous observations supporting these models are reviewed, and a case of dense magnetotail boundary layer plasma and strongly bent field lines observed by ISEE 3 is examined. Observations of boundary layer plasma within a tangential discontinuity magnetopause are discussed. The model to explain this phenomenon requires that interconnected magnetotail and magnetosheath field lines leave the magnetotail via a narrow 'window'. Field lines in the dense boundary layer plasma veer away from the aberrated x axis more than those in the void magnetotail lobes in order to pass through the windows. Magnetosheath plasma must enter the magnetotail lobes through the windows at all downstream distances in order to supply he observed tailward flux of lobe plasma.

Sibeck, D. G.↗

NASA NTRS1985

Solar wind-magnetosphere coupling and the distant magnetotail: ISEE-3 observations

ISEE-3 Geotail observations are used to investigate the relationship between the interplanetary magnetic field, substorm activity, and the distant magnetotail. Magnetic field and plasma observations are used to present evidence for the existence of a quasi-permanent, curved reconnection neutral line in the distant tail. The distance to the neutral line varies from absolute value of X = 120 to 140 R/sub e near the center of the tail to beyond absolute value of X = 200 R/sub e at the flanks. Downstream of the neutral line the plasma sheet magnetic field is shown to be negative and directly proportional to negative B/sub z in the solar wind as observed by IMP-8. V/sub x in the distant plasma sheet is also found to be proportional to IMF B/sub z with southward IMF producing the highest anti-solar flow velocities. A global dayside reconnection efficiency of 20 +- 5% is derived from the ISEE-3/IMP-8 magnetic field comparisons. Substorm activity, as measured by the AL index, produces enhanced negative B/sub z and tailward V/sub x in the distant plasma sheet in agreement with the basic predictions of the reconnection-based models of substorms. The rate of magnetic flux transfer out of the tail as a function of AL is found to be consistent with previous near-Earth studies. Similarly, the mass and energy fluxes carried by plasma sheet flow down the tail are consistent with theoretical mass and energy budgets for an open magnetosphere. In summary, the ISEE-3 Geotail observations appear to provide good support for reconnection models of solar wind-magnetosphere coupling and substorm energy rates.

Slavin, J. A.↗

NASA NTRS1985

Solar wind flow about the outer planets - Gas dynamic modeling of the Jupiter and Saturn bow shocks

It has been found that the solar wind is diverted about planets through the formation of bow shocks which heat and deflect the flow. These observations are based on missions concerned with Mercury, Venus, earth, and Mars during the 1960s and 1970s. The present study has the objective to extend to Jupiter and Saturn certain aspects of the analyses which have been carried out on the terrestrial planets. In particular, the Pioneer 10 and 11 and Voyager 1 and 2 observations near Jupiter and Saturn are used to characterize the relevant upstream flow parameters at 5 and 9 AU. Attention is given to solar wind parameters, bow shock and magnetopause models, and the solar wind standoff distance, and aspects of gas-dynamic modeling.

Slavin, J. A.↗

NASA NTRS1985

The distant magnetotail's response to a strong interplanetary magnetic field By - Twisting, flattening, and field line bending

During an interval of strong interplanetary magnetic field (IMF) By, while ISEE 3 was in the distant magnetotail, the north lobe was observed south of the ecliptic plane. Lobe field lines were strongly bent in the direction of the IMF, and a dense boundary layer plasma was observed. During the interval, magnetopause normals pointed in the z direction, although ISEE 3 was near the dawnside ecliptic plane. The observations are interpreted in terms of field line bending within a twisted and flattened magnetotail.

Sibeck, D. G.↗

NASA NTRS1985

Coupling between the solar wind and the magnetosphere - CDAW 6

It is pointed out that an extensive study of the causes and manifestations of geomagnetic activity has been carried out as part of the sixth Coordinated Data Analysis Workshop, CDAW 6. The present investigation has the objective to determine the coupling between the solar wind and the magnetosphere for the two selected analysis intervals, taking into account, as a basis for the study, the interplanetary field and plasma observations from ISEE 3 and IMP 8 and the geomagnetic activity indicators developed by CDAW 6 participants. The method of analysis employed is discussed, giving attention to geomagnetic indices, upstream parameters, and a cross-correlation analysis. In a description of the obtained results, the March 22, 1979 event is considered along with the March 31 to April 1, 1979 event, and an intercomparison of the events. The relationship between interplanetary indices and the resulting geomagnetic activity for the two CDAW 6 intervals is illustrated.

Tsurutani, B. T.↗

NASA NTRS1985

Magnetotails of the terrestrial planets: A comparative study

Spacecraft observations have established that all of the terrestrial planets interact strongly with the solar wind and possess well developed magnetic tails. At Mercury, Earth, and possibly Mars the tail forms as a result of the solar wind dragging back field lines intrinsic to the planet. Venus differs dramatically from the other planets in that its magnetotail is composed of interplanetary field lines draped about the ionopause. Accordingly, the observations made at the terrestrial planets provide an opportunity to compare not only induced (Venus) magnetic tail properties with those of intrinsic field tails, but also the variation among intrinsic field tails ion the limits of no ionosphere (Mercury), weak intrinsic magnetic field (Mars), and strong magnetic field and ionosphere (Earth). A comparative investigation is made of terrestrial planet magnetotail structure and dynamics. The results are discussed in terms of the physical properties of these planets and their interactions with the solar wind.

Slavin, J. A.↗

NASA NTRS1984

Evolution of the earth's distant magnetotail - ISEE 3 electron plasma results

ISEE 3 data form the basis for a study of the evolution of the electron plasma in the magnetotail lobe and plasma sheet regions as a function of radial distance from the earth. The data were plasma electron and magnetometer measurements taken when the ISEE 3 was tailward of the earth during three different orbits. About 91,000 electron spectra were obtained in terms of the magnetosheath, lobe, plasma sheet and radial downstream distances. The lobe density peaked at 60 earth radii, while the sheet density tapered very slowly downstream. At large downstream distances (about 180 radii), the plasma bulk flow velocity increased significantly, surpassing the solar wind velocity. The bimodal electron flow angle near the earth became a single tailward flow at 180 radii.

Zwickl, R. D.↗

NASA NTRS1984

Direct observations of passages of the distant neutral line (80-140 RE) following substorm onsets - ISEE-3

Specific events recorded by ISEE-3 passage through the earth magnetotail at 80-140 earth radii are discussed. The data were taken during March 20-28, 1983, when Kp ranged from +6 to -40, and included both plasma and magnetic field signatures. Magnetic field polar angle reversals from N-S flows were detected, along with alteration in the bulk plasma flow from tailward to stagnation. Tailward flow was associated with negative field values, while stagnation was mainly present with positive field values. The tail plasma at 100 radii exhibited changes shortly after a substorm event which featured particle ejection at 6.6 earth radii. The plasma sheet swept by the events could have a 25-50 radii length scale.

Baker, D. N.↗